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PROFESSOR   LADD'S  WORKS 


OUTLINES  OF  DESCRIPTIVE  PSYCHOLOGY.  A  Text-Book 
of  Mental  Science  for  Colleges  and  Normal  Schools.  8vo. 
$1.50  net 

PSYCHOLOGY:  DESCRIPTIVE  AND  EXPLANATORY.  A 
Treatise  of  the  Phenomena,  Laws,  and  Development  of 
Human  Mental  Life.    8vo.    $4.50. 

OUTLINES  OF  PHYSIOLOGICAL  PSYCHOLOGY.  A  Text- 
Book  of  Mental  Science  for  Academies  and  Colleges.  Il- 
lustrated.   8vo.    I2.00. 

ELEMENTS  OF  PHYSIOLOGICAL  PSYCHOLOGY.  A  Treat- 
ise of  the  Activities  and  Nature  of  the  Mind,  from  the 
Physical  and  Experimental  Point  of  View.  With  nu- 
merous illustrations.    8vo.     $4.50. 

PRIMER   OF   PSYCHOLOGY.     i2mo.     $1.00  net. 

PHILOSOPHY  OF  MIND.  An  Essay  in  the  Metaphysics  of 
Psychology.    8vo.    I3.00. 

PHILOSOPHY  OF  KNOVi^LEDGE.  An  Inquiry  into  the 
Nature,  Limits,  and  Validity  of  Human  Cognitive  Fac- 
ulty.   8vo     $4.00. 

INTRODUCTION  TO  PHILOSOPHY.  An  Inquiry  after  a 
Rational  System  of  Scientific  Principles  in  their  Relation 
to  Ultimate  Reality.    8vo.     I3.00. 

THE  DOCTRINE  OF  SACRED  SCRIPTURE.  A  Critical,  His- 
torical, and  Dogmatic  Inquiry  into  the  Origin  and  Nature 
of  the  Old  and  New  Testaments.     2  vols.    8vo.    I7.00. 

WHAT  IS  THE  BIBLE?  An  Inquiry  into  the  Origin  and 
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Modern  Biblical  Study.    i2mo.    $2.00. 

THE  PRINCIPLES  OF  CHURCH  POLITY.  Crown  8vo.    $2.50. 


ELEMENTS 


Physiological  Psychology 


A  TREATISE  OF  THE  ACTIVITIES  AND  NATURE 
OF   THE  MIND 


FROM  THE  PHYSICAL  AND  EXPERIMENTAL  POINT  OF  VIEW 


BY 

GEORGE  T.  LADD 

PKOFESSOE  OF  PHILOSOPHY  IN  YALE  CNIVERSITy 


NEW  YORK 

CHARLES    SCRIBNER'S    SONS 

1900 


COPTBIGHT,  1887,  BT 
CHARLES  SCRIBNEE'S  SONS 


TROW   DIRECTORY 

PRINTING  AND   BOOKBINDING  COMPANY 

NEW  YORK 


PREFACE. 


-«3 


There  can  be  no  doubt  that  an  important  movement  in  psychol- 
ogy has  arisen  in  recent  times  through  the  effort  to  approach  the 
phenomena  of  mind  from  the  experimental  and  physiological  point 
of  view.  Different  students  of  psychological  science  will  estimate 
differently  both  the  net  result  already  reached  by  this  effort  and 
the  promise  of  further  additions  to  the  sum  of  our  knowledge  from 
continued  investigation  of  the  same  kind.  Some  writers  have  cer- 
tainly indulged  in  extravagant  claims  as  to  the  past  triumphs  of  so- 
called  Physiological  Psychology,  and  in  equally  extravagant  expec- 
tations as  to  its  future  discoveries.  On  the  other  hand,  a  larger 
number,  perhaps,  have  been  inclined  either  to  fear  or  to  depreciate 
every  attempt  to  mingle  the  methods,  laws,  and  speculations  of  the 
physical  sciences  with  the  study  of  the  human  soul.  These  latter 
apparently  anticipate  that  some  discovery  in  the  localization  of 
cerebral  function,  or  in  psychometry,  may  jeopard  the  birthright 
of  man  as  a  spiritual  and  rational  being.  Or  possibly  they  wish 
to  regard  the  soul  as  separated,  by  nature  and  with  respect  to  its 
modes  of  action,  from  the  material  body  in  such  a  way  as  to  render 
it  impossible  to  understand  more  of  the  one  by  learning  more 
about  the  other. 

As  a  result  of  some  years  of  study  of  the  general  subject,  I  express 
with  considerable  confidence  the  opinion  that  there  is  no  grormd  for 
extravagant  claims  or  expectations,  and  still  less  ground  for  any  fear 
«f  of  consequences.     In  all  cases  of  new  and  somewhat  rankly  growing 

^  scientific  enterprises,  it  is  much  the  better  way  to  waive  the  discus- 

g  sion  of  actual  or  possible  achievements,  as  well  as  of  welcomed  or 

;*  dreaded  revelations  of  new  truth,  and  proceed  at  once  to  the  busi- 

^  ness  on  hand.    It  is  proposed  in  this  book  to  follow  this  better  way. 

It  will  be  the  task  of  the  book  itself  to  set  forth  the  assured  or  al- 
leged results  of  Physiological  Psychology ;  and  this  will  be  done  at 


Ul 
Q 


352441 


iv  PEEFACE. 

every  step  with  such  degree  of  assurance  as  belongs  to  the  evidence 
hitherto  attainable  upon  the  particular  subject  discussed.  With 
declamation,  either  in  attack  or  defence  of  the  "  old  psychology," 
of  the  "  introspective  method,"  etc.,  one  may  dispense  without  seri- 
ous loss. 

The  study  of  the  phenomena  of  consciousness  by  the  method  here 
proposed  necessarilj'  requires  some  acquaintance  with  a  consider- 
able circuit  of  sciences  which  are  not  usually  all  alike  closely  allied. 
The  number  of  scholars  who  can  form  opinions  with  equal  freedom 
and  confidence  in  all  of  these  sciences  is  very  small.  Moreover, 
since  all  psycho-physical  laws  ai'e  supposed — as  the  very  term  indi- 
cates— to  govern  the  correlations  of  phenomena  of  consciousness 
with  phenomena  of  the  nervous  sj'stem,  a  peculiar  mystery  belongs 
to  much  of  the  domain  within  which  psycho-physical  science  is  com- 
pelled to  move.  These  facts  may  fitly,  on  the  one  hand,  excite 
caution  in  the  writer ;  and,  on  the  other  hand,  excuse  him  for  many 
inevitable  failures  to  set  forth  with  perfect  definiteness  and  confi- 
dence the  conclusions  he  has  to  propose.  Much  will  be  said  that 
must  be  accepted  as  provisional,  as  only  probably  true.  Much 
room  must  also  be  made  for  conjecture  and  speculation.  What  is 
most  important,  however,  is  that  conjecture  should  not  be  put  forth 
as  ascertained  fact,  or  speculation  as  unquestioned  law. 

It  would  have  been  a  great  assistance  to  me  if  I  had  had  more 
predecessors  in  the  path  which  I  am  to  take.  But  with  the  ex- 
ception of  Wundt's  masterly  work  (Grundziige  der  physiologischen 
Psychologic,  second  edition  in  1880),  no  one  book  has  attempted  to 
cover,  even  in  a  summary  way,  the  entire  ground.  The  number  of 
monographs,  however,  which  have  dealt  with  individual  questions 
subordinate  to,  or  part  of,  the  main  inquiry  is  very  great.  These 
two  facts  also  render  the  attempt  at  a  general  survey  of  Physiolog- 
ical Psychology  for  readers  of  English  both  peculiarly  attractive 
and  peculiai-ly  difiicult.  I  can  only  indulge  the  hope  that  I  have 
done  something  toward  breaking  this  path  and  rendering  it  easier 
and  more  secure,  both  for  mj'self  and  for  others,  in  the  future. 

The  investigatox'S  and  authors  to  whom  I  am  under  obligations 
for  material  upon  the  various  questions  discussed,  or  statements 
made,  in  this  book  are  by  no  means  all  mentioned  by  name.  Of 
course,  much  of  what  is  said  on  the  structure  of  the  nervous  system, 
and  on  the  phenomena  of  sensation  and  perception,  has  already 
become  part  of  that  general  fund  of  facts  and  laws  which  belongs 
alike  to  all  students  of  the  subject.    But  by  quoting  certain  author- 


PEEFACE.  V 

ities  in  the  text,  and  by  a  few  (in  comparison  with  the  number 
which  might  have  been  cited)  references  in  foot-notes,  I  have  con- 
nected some  of  the  discoveries  and  views  of  modern  psycho-physical 
science  with  their  authors.  These  may  serve  somewhat  as  guide  to 
those  persons  who  wish  to  pursue  such  studies  still  further. 

I  am  under  particular  obligations  to  Dr.  James  K.  Thacher,  Pro- 
fessor of  Physiology  in  the  Yale  Medical  School,  for  valuable  as- 
sistance in  that  description  of  the  Nervous  Mechanism,  its  structure 
and  functions,  which-  the  First  Part  of  the  book  contains.  If  I 
have  escaped  the  mistake  of  assuming  to  teach  more  than  is  really 
known  upon  this  subject,  it  has  been  in  large  measure  due  to  his 
friendly  and  skilful  guidance.  Valuable  assistance  has  also  been 
received  from  Kussell  H.  Chittenden,  Professor  of  Physiological 
Chemistry,  and  Charles  S.  Hastings,  Professor  of  Physics — both  of 
the  Sheffield  Scientific  School. 

The  method  and  arrangement  of  the  book  have  been  chosen  so 
as  to  fit  it  for  use,  both  as  a  text-book  by  special  students  of  the 
subjects  of  which  it  treats,  and  also  by  the  general  reader  who  is 
interested  in  knowing  what  results  have  been  reached  by  the  more 
modern — and  even  the  latest — psycho-physical  researches. 

George  T.  Ladd. 

Yale  Univeksity,  New  Haven,  February,  1887. 


TABLE    OF    CONTENTS. 


PAGE 

Introduction 1-14 


PART    EIRST. 
THE  NERVOUS  MECHANISM. 

CHAPTER  I. 

The  Elements  of  the  Nervous  System 17-55 

§§  1-4,  General  Function  of  the  Nervous  System. — §§  5-16,  Chem- 
ical Constitution  of  the  Nervous  Elements. — §§  17-30,  Structural 
Form  of  the  Nervous  Elements. — §§  31-36,  Common  Properties  of 
the  Nervous  Elements. 

CHAPTER  n. 

Combination  of  the  Nervous  Elements  into  a  System 56-101 

§§  1-3,  Threefold  Plan  of  the  Nervous  System.— §  4,  The  Sympa- 
thetic and  Cerebro-spinal  Systems. — §  5,  Membranes  of  Brain  and 
Spinal  Cord.— §§  6-13,  Structure  of  the  Spinal  Cord.— §§  13-14, 
General  Arrangement  of  the  Encephalon. — §  15,  Structure  of  the 
Medulla  Oblongata.— §16,  Structure  of  the  Cerebellum.— §  17,  Struct- 
ure of  the  Pons  Varolii.— §§  18-24,  Structure  of  the  Cerebrum. — 
§§  25-27,  Cortex  of  the  Cerebral  Hemispheres.— §§  28-29,  Arrange- 
ment of  the  Nerve-Tracts. — §  30,  The  Cranial  and  Spinal  Nerves. 

CHAPTER  IIL 

The  Nerves  as  Conductors 102-129 

§§  1-3,  General  Oflce  of  the  Nerves.— §  4,  The  Nerve-Muscle  Ma- 
chine.—§§  5-8,  The  Conditions  of  Neural  Action.— §§  9-19,  Phenom- 
ena induced  in  the  Nerves  by  different  Stimuli.— §§  20-23,  Electrical 
and  other  Processes  in  the  excited  Nerve-Stretch.— §§  24-26,  Laws 


Viii  TABLE   OF   CONTENTS. 

of  the  Nerve-Commotion. — §  27,  Speed  of  the  Nerve-Commotion. — 
§  28,  Effect  of  Section.— §  29,  Nervous  Conduction  in  the  Central  Or- 
gans.—i;§  30-32,  Paths  of  Conduction  in  the  Spinal  Cord.— §§  33-35, 
Paths  of  Conduction  in  the  Brain. 


CHAPTER  IV. 

PAGB 

Automatic  AND  Reflex  Functions  of  the  Central  Organs..  130-162 

§§  1-2,  Nature  and  Kinds  of  Reflex  Action.— §§  3-5,  TheSpinal 
Cord  as  a  Central  Organ. — ^§  6-9,  Laws  of  Spinal  Reflexes.— §  10, 
Irregular  Automatism  of  the  Cord. — §  11,  Centres  of  the  Cord. — t^  12, 
Excitability  of  the  Cord.— §  13,  Inhibition  of  the  Cord. — §  14,  The 
Brain  as  a  Central  Organ. — §§  15-16,  Functions  of  the  Medulla  Ob- 
longata—-§§  17-19,  Centres  of  the  Medulla  Oblongata.— §  20,  Influ- 
ence of  the  Cerebral  Lobes, — §  21,  Functions  of  the  Cerebellum. — 
g§  22-27,  Functions  of  the  Basal  Ganglia.— §  28,  Gray  Matter  of  the 
Third  Ventricle. 

CHAPTER  V. 

End-Organs  of  the  Nervous  System 163-197 

§y  1-2,  Characteristics  of  the  End-Organs. — §  3,  The  Kinds  of  End- 
Organs.— §^  4-5,  The  End-Organs  of  Smell.— §§  6-7,  The  End-Or- 
gans of  Taste.— §§  8-10,  The  End-Organs  of  Touch.— §  11,  The  End- 
Organ  of  Sight. — §§  12-16,  Tunics,  Media,  and  Appendages  of  the 
Eye. — g  17,  The  Mechanism  of  Accommodation. — §§  18-21,  Structure 
and  Functions  of  the  Retina — §  22,  Photo-Chemistry  of  Vision. — 
§§  23-26,  External  and  Middle  Ear.— §  27,  Structure  of  the  Labyrinth. 
■ — §  28,  End-Apparatus  of  the  Vestibule.  — §  29,  The  Organ  of  Corti. — 
§§"30-31,  Problem  solved  by  the  Labyrinth.— §  32,  End-Organs  of 
Motion. 

CHAPTER  VI. 

The  Development  of  the  Nervous  Mechanism 198-21 S 

§  1,  Nature  of  Embryonic  Life. — §§  2-5,  Earliest  Development  of 
the  Ovum. — §§  6-8,  Blastodermic  Layers  and  their  Differentia. — §§  9- 
11,  Head-Fold  and  Brain-Vesicles. — §  12,  Development  of  Cranial 
and  Spinal  Nerves. — §§  13-15,  Subsequent  Development  of  the 
Brain. — §§  16-17,  Development  of  Eye  and  Ear. — §  18,  Histogenetic 
Changes  in  the  Embryo. — §  19,  Conclusions. 

CHAPTER  VII. 

Mechanical  Theory  of  the  Nervous  System 214-23(1 

§  1,  Machine-like  Nature  of  the  Body.— §§  2-6,  The  Nervous  Sys- 
tem as  a  Mechanism. — §  7,  Summation  and  Interference  in  Nerves. — 
i^  8,  Evidence  from  the  Electrical  Phenomena. — i^  9,  Theory  of  du 
Bois-Roymond. — §^5  10-11,  Theory  of  Hermann. — S^i5  12-13,  Theory 
of  Wundt. — §§  14-15,  General  Conclusions  as  to  a  Mechanical  Theory. 


TABLE   OF   CONTENTS.  IX 


PART    SECOND. 


CORRELATIONS   OF  THE  NERVOUS  MECH- 
ANISM AND  THE  MIND. 


CHAPTER  I. 

PAGE 

The  Localization  of  Cerebral  Function 239-263 

§§  1-3,  Proofs  of  the  Brain's  Special  Significance. — §§  4-7,  The 
Brain  as  a  Measure  of  Intelligence. — §  8,  Special  Significance  of  the 
Cerebral  Hemispheres. — ^§  9-10,  The  Question  of  Localization. — 
§§  11-13,  The  History  of  Discovery.— §g  14-16,  The  Evidence  from 
Experiment.— §  17,  The  Evidence  from  Pathology.— §  18,  The  Evi- 
dence from  Anatomy. — §  19,  True  Method  of  Investigation. 


CHAPTER  IL 

The  Localization  of  Cerebral  Function  [Continued] 263-802 

§§  1-4,  Difliculties  from  Negative  Cases. — §§  5-6,  Experiments  in 
Stimulation. — ^  7,  Experiments  in  Extirpation. — ^§  8-9,  Nature  of 
so-called  Motor  Centres. — §§  10-15,  Method  and  Results  of  Bxner. — 
§  16,  Confirmatory  Conclusions  from  other  Sources. — §  17,  The  Evi- 
dence of  Histology. — §  18,  Relation  of  Motion  and  Sensibility. — §§  19- 
21,  Visual  and  Auditory  Centres  of  Ferrier  and  Munk. — ^  22,  Ex- 
ner's  Cerebral  Field  of  Vision. — g  23,  Relations  between  the  Retinas 
and  the  Cerebrum. — §  24,  Localization  of  Smell  and  Taste. — §§  25- 
27,  The  Phenomena  of  Aphasia. — §  28,  Cerebral  Lesions  in  Aphasia. 
— §  29,  Conjectures  as  to  the  Frontal  Lobes. — §  30,  Negative  Conclu- 
sions of  Goltz. — §  31,  Conclusion  as  to  three  leading  Principles. 

CHAPTER  III. 

The  Quality  op  Sensations 303-324 

§§  1-5,  Sensations  and  Things. — §  6,  The  Subjects  investigated. — 
§  7,  Specific  Energy  of  the  Nerves. — §§  8-11,  Sensations  of  Smell. 
— §§  12-15,  Sensations  of  Taste.— §§  16-17,  The  Varieties  of  Sound. 
— §§  18-20,  The  Pitch  of  Tones. -^§§  21-22,  The  Composition  of 
Clangs. — §  23,  Analysis  of  Sounds  by  the  Ear. 

CHAPTER  IV. 

The  Quality  of  Sensations  [Continued] 325-355 

§  1,  Analysis  of  Sensations  of  Sight. — §§  2-3,  The  Stimulus  of  Sight. 
— §  4,  Relation  of  Quality  and  Quantity. — §§  5-8,  The  Different  Color- 


TABLE   OF   CONTENTS. 

Tones. — §  9,  The  Complementary  Colors. — §§  10-13,  Conditions  of 
Changes  in  Coloi-. — §  14,  Phenomena  of  Contrast. — §§15-17,  Theories 
of  Visual  Sensations. — §  18,  Symbolism  of  Visual  Sensations. — §  19, 
Sensations  of  the  Skin. — §  30,  The  Muscular  Sensations. — §  21,  Sen- 
sations of  Pressure. — §§  22-24,  Sensations  of  Temperature. — §  25, 
Specific  Energy  of  the  Nerves. 


CHAPTEK  V. 

FAOg 

The  QuAwriTY  of  Sensations 356-381 

§§  1-3,  Distinction  of  Variations  in  Quantity. — §§  4^5,  The  Meas- 
urement of  Sensations. — §  6,  Nature  of  the  Least  Observable  Differ- 
ence.— §  7,  The  Determining  of  the  Limits. — §  8,  Methods  of  Experi- 
ment.— §  9,  Statement  of  Weber's  Law. — §  10,  Measurement  of 
Sensations  of  Pressure. — §  11,  Measurement  of  Sensations  of  Tem- 
perature.—§§  12-15,  The  Intensity  of  Sounds.— §§  16-18,  The  In- 
tensity of  Visual  Sensations. — ^§  19-21,  Measurement  of  Taste  and 
Smell.— §§  32-23,  Value  of  Weber's  Law. 


CHAPTBE  VI. 

The  Presentations  of  Sense 382-419 

§§  1-2,  Sensations  and  Things. — §  3,  General  Nature  of  the  Pres- 
entations of  Sense. — §§  4-5,  Laws  of  the  Synthesis  of  Sensations. — 
§§  6-7,  Nativistic  and  Empiristic  Theories. — §§  8-11,  Nature  of  the 
Spatial  Series.— §§  12-15,  The  Theory  of  Local  Signs.— §  16,  The 
Stages  of  Perception. — §  17,  Perceptions  of  Smell.  — §  18,  Perceptions 
of  Taste.— §§  19-20,  Perceptions  of  Hearing.— §§  21-22,  Sense  of  Lo- 
cality by  the  Skin.— §§  23-25,  Weber's  Sensation-Circles.— §  26,  The 
Discernment  of  Motion. — §  27,  Localizing  of  Temperature-Sensa- 
tions.— §  28,  Localizing  of  Muscular  Sensations. — §§  29-30,  Construc- 
tion of  the  Field  of  Touch. — §  31,  Feelings  of  Double  Contact. 


CHAPTEK  Vn. 

The  Presentations  of  Sense  [Continued] 420-46'] 

§  1,  General  Principles  ai)plied  to  the  Eye. — §  3,  Data  or  Motifs  of 
Vision. — §§  3-6,  Nature  of  the  Primary  Retinal  Field. — §  7,  Value  of 
the  Retinal  Elements. —ij^  8-9,  Motions  of  the  Eye.— §  10,  The  Law 
of  Listing. — §  11,  Meridians  of  the  Field  of  Vision. — §  12,  Effect  of 
Accommodation. — i:§  13-16,  Single  and  Double  Images.— §  17,  The 
Fixation  of  Attention.— §§  18-20,  Stereoscopic  Vision  and  Vision  of 
Perspective.- §§  21-23,  The  Use  of  Secondary  Helps.— §§  24-25, 
General  Office  of  Experience. — §§  26-28,  Judgment  of  Spatial  Exten- 
sion and  Relations.— i^  29,  Visual  Perception  of  Motion.— §§  30-34, 
Errors  of  Sense.— §  35,  Development  of  Visual  Percei:)tiou. 


TABLE  OF  CONTENTS.  XI 


CHAPTER  Vm. 

PAGE 
TrME-REIiATIONS  OF  MENTAL  PHENOMENA 468-497 

§§  1-3,  Time-Form  as  belonging  to  Mental  Phenomena. — i^§  3-4, 
Elements  of  Physiological  and  Psycho-physical  Time. — §§  5-7,  Effect 
of  the  Inertia  of  the  Nervous  System. — §§  8-12,  Nature  and  Length 
of  Simple  Reaction-Time. — §§  13-15,  Methods  for  discovering  Ap- 
perception-Time.— §§  16-18,  Length  of  Apperception-Time. — §§  19- 
30,  Nature  of  Will-Time.— §§  21-23,  Subjective  Estimate  of  Time.— 
§§  24-85,  Reaction-Time  of  complex  Mental  Processes. — §  86,  The 
Circuit  of  Consciousness.  — §  37,  Various  Influences  upon  Psycho-phys- 
ical Time. — §  88,  Conclusions. 


CHAPTER  IX. 

Feelings  and  Motions 498-581 

§  1,  Nature  of  the  Inquiry. — §§  3-4,  Physiological  Theory  of  the 
Nature  of  Feeling. — §§  5-7,  Psychological  Theory  of  the  Nature  of 
Feeling. — §^  8-9,  Classification  of  the  Feelings. — §§  10-11,  Charac- 
teristics of  all  Feeling. — §  13,  Physical  Apparatus  of  Feeling. — §§  13- 
14,  Nature  of  Common  Feeling. — §§  15-18,  Feelings  of  Sensation. — 
§§  19-31,  The  Emotions.— §  33,  Mental  Moods.— §§  33-34,  The  Es- 
thetic Feelings.  — §  35,  The  Intellectual  Feelings.— §  36,  The  Feeling 
of  Effort. — §§  27-31,  Voluntary  and  Involuntary  Movements. 


CHAPTER  X. 

Physical  Basis  of  the  Higher  Faculties 533-559 

§§  1-3,  The  Method  of  Investigation. —§§  4-6,  Physiological  Basis 
of  Acts  of  Will.— §§  7-9,  The  Will  in  Attention.— §§  10-11,  Cerebral 
Processes  in  Attention. — §  13,  Freedom  of  Will. — §  13,  Physical  Basis 
of  Consciousness. — §§  13-14,  Physiological  Basis  of  Memory. — §§  15- 
17,  Memory  as  Retentive. — §§  18-19,  Memory  as  Reproductive. — 
§§  30-31,  Organic  Memory. — §  33,  Memory  as  a  Psychical  Process. 
— §  33,  Physical  Basis  of  Conception. 


CHAPTER  XI. 

Certain  Statical  Relations  of  the  Body  and  Mental  Phe- 
nomena    560-583 

§§  1-3,  Popular  Estimate  of  the  Relations  of  Body  and  Mind. — 
§§  3-9,  Relations  Dependent  on  Age  and  Development. — §§  10-18, 
Relations  Dependent  on  Sex. — §  13,  Characteristics  of  different  Races. 
— §  14,  The  Theory  of  Temperament. — §§  15-17,  Kinds  of  Tempera- 
ment.— §  18,  Physical  Basis  of  Temperament. — §  19,  General  Corre- 
lations of  Body  and  Miud. 


XU.  TABLE  OF  CONTENTS. 

PART  THIRD. 
THE  NATURE   OF  THE  MIND. 


CHAPTEE  I. 

PAGE 

The  Faculties  of  the  Mind,  and  its  Unity   585  -613 

§§  1-4,  The  Method  of  Investigation. — §§  5-6,  Mental  Phenomena 
and  Cerebral  Changes. — §§  7-9,  Physical  Theory  of  the  Cause  of 
Psychical  States.— §  10,  The  Subject  of  Psychical  States.— g§  11-13, 
Variety  of  the  Phenomena  of  Consciousness  — ^§  14-16,  Classification 
of  Psychical  States.— §  17,  Nature  of  the  Mental  Faculties.— §§  18-23, 
The  Unity  of  Consciousness. 

CHAPTER  11. 

The  Development  of  the  Mind 614-632 

§§  1-2,  Genetic  Study  of  the  Mind.— §§  3-5,  Reality  of  Mental 
Development. — §§  6-8,  Stages  of  Mental  Development.— §§  9-10, 
Dependence  of  Mental  on  Physical  Growth.— §  11,  Psychical  Factors 
in  Development.— §§  12-16,  The  Theory  of  Mental  Evolution. 

CHAPTER  III. 

Real  Connection  of  Brain  and  Mind 633-667 

§  1,  General  Question  of  a  Connection  of  Brain  and  Mind. — §§  2-6, 
The  Brain  as  the  "  Seat"  of  the  Mind.— §§  7-9,  The  Brain  as  the 
"Organ"  of  the  Mind. — §  10,  Special  "Bond"  between  Brain  and 
Mind. — §  11,  Figurative  Connection  of  Brain  with  Mind. — §  12,  Causal 
Relation  of  Brain  and  Mind. — §§  13-14,  Occasionalism  and  Pre-estab- 
lished Harmony. — §  15,  Positivism  and  Monism. — §  16,  The  Position 
of  Dualism. — §  17,  Conservation  and  Correlation  of  Energy. — §§  18- 
24,  The  Causal  Nexus  declared  Valid. 

CHAPTER  IV. 

The  Mind  as  Real  Being 668-688 

§  1,  The  Metaphysical  Treatment  of  Mind.— §§  2-8,  The  Mind  as 
a  Real  Being.— §§  9-10,  The  Spirituality  of  Mind.— §§  11-15,  The 
Unity  of  Mind.— §  16,  First  and  Last  Things  of  the  Mind. 


PHYSIOLOGICAL   PSYCHOLOGY. 


nSTTEODUOTIOH. 

§  1.  A  CLEAR  conception  oi  Physiological  Psychology  requires  some 
special  knowledge  of  the  nature  and  methods  of  those  two  sci- 
ences, the  results  of  whose  investigation  it  endeavors  to  combine. 
These  sciences  are,  of  course,  Psychology  and  Physiology — the  latter 
being  understood  in  a  broad  way  as  including  also  various  apphca- 
tions  of  the  general  theory  of  physics  to  the  functions  of  the  animal 
organism.  But  as  the  form  taken  by  this  compound  term  would 
itself  seem  to  indicate,  the  two  do  not  stand  upon  precisely  the 
same  level  in  effecting  this  combination,  whether  we  consider  the 
end  that  the  one  science  into  which  both  enter  desires  to  reach, 
or  the  means  that  it  employs  to  reach  the  end.  For  the  noun 
("psychology")  in  the  compound  term  may  be  said  more  particu- 
larly to  define  the  end  desired;  the  adjective  ("physiological") 
the  character  of  the  means  which  it  is  proposed  especially  to  em- 
ploy. Hence  "Physiological  Psychology"  can  scarcely  claim  to  be 
an  independent  science,  or  even  a  definite  branch  of  the  science  of 
psychology  in  general.  It  is  rather  to  be  regarded  simply  as  psychol- 
ogy approached  and  studied  from  a  certain — the  so-called  "  physi- 
ological " — side  or  point  of  view.  It  is  necessary,  then,  in  the  first 
place,  to  define  what  we  understand  by  the  science  of  psychology, 
and  how  it  is  proposed  to  treat  this  science  as  subject  to  the  physi- 
ological method,  and  as  approached  by  means  of  physiological  ex- 
perimentation and  researches. 

§  2.  Perhaps  the  most  common  definition  of  psychology,  up  to  the 
present  time,  has  regarded  it  as  "  the  science  of  the  human  soul." 
If  this  definition  had  always  been  given,  on  beginning  the  pursuit 
of  the  science,  only  in  a  provisional  way,  and  with  the  implied  or 
open  confession  that  it  is  the  business  of  psychology  itself  to  de- 
monstrate the  existence  of  a  particular  entity  called  "  the  soul,"  and 


2  INTRODUCTION". 

to  show  how  this  entity  is  needed  to  explain  the  phenomena  of  con- 
sciousness, then  httle  valid  objection  could  have  been  made  to 
it.  But  such  has  by  no  means  been  the  case.  For  example, 
one  writer  on  the  subject  (Drbal),  at  the  very  commencement  of 
his  treatise,  asserts  that  "psychology  is  the  science  of  the  human 
soul  as  the  real  foundation  of  the  spiritual  life  ; "  and  another  (Erd- 
mann)  declares  that  "  the  subject-matter  of  psychology  is  the  sub- 
jective spirit,"  meaning  by  this  term  the  human  soul.  Objections 
have,  therefore,  been  more  or  less  fitly  and  forcefully  urged  agninst 
this  definition  as  ordinarily  employed.  It  has  been  said  that  clearly 
■we  have  no  right  to  assume  any  such  entity  as  the  soul ;  and 
even  that  a  careful  study  of  all  the  phenomena — especially  by  the 
experimental  and  physiological  method — does  not  compel  or  induce 
us  to  conclude  that  such  entity  exists.  It  has  been  claimed,  espe- 
cially of  late,  that  there  may  be  a  "  psychology  without  a  soul,"  and, 
indeed,  that  this  kind  of  psychology  is  alone  worthy  of  being  con- 
sidered truly  scientific.  Further  objection  to  the  same  definition 
has  been  made  in  other  quarters,  because  it  seems  to  regard  the 
question  as  settled,  whether  man  has  not  moi-e  than  one  subject  (or 
"ground")  of  the  manifold  phenomena  called  psychical ;  whether, 
in  fact,  he  may  not  be  the  fortunate  possessor  of  both  an  "  animal " 
and  a  "rational"  soul,  etc.  It  would  be  aside  from  the  course  of 
our  inquiries  to  consider  these  objections  in  detail  at  this  time  ;  or 
to  state  at  any  length  how  far  we  are  inclined  to  agree  with  them  and 
how  far  to  express  dissent.  They  may  all  be,  for  the  present,  set 
aside  by  stating  the  course  of  procedure  which  the  study  of  psy- 
chology from  the  physiological  point  of  view  seems  to  us  plainly  to 
recommend. 

The  satisfactory  definition  of  any  science  is  often  one  of  the  latest 
and  most  difficult  achievements  of  that  science.  When  such  defini- 
tion is  placed  at  the  beginning  of  an  investigation,  it  must  often 
really  include  results  reached  only  by  going  carefully  and  repeatedly 
over  the  entire  ground  of  the  science.  In  all  such  cases  the  learner 
of  the  science  is  quite  unable  fully  to  comprehend  the  definition,  or 
to  understand  the  positions  upon  various  disputed  questions  which 
it  may  really  involve.  In  general,  then,  it  is  better  that  the  earliest 
so-called  definition  should  be  simply  a  description  of  that  class  of 
phenomena  which  it  is  proposed,  as  far  as  possible,  to  isolate  for 
purposes  of  inquiry.  This  remark  applies  with  peculiar  force  to 
psychology,  both  on  account  of  such  objections  as  those  mentioned 
above,  and  also  on  account  of  certain  difficulties  inherent  in  the 
subject  itself.  Accordingly,  it  will  serve  our  purpose  best  to  "de- 
fine "  this  science  simply  by  ascribing  to  it  a  certain  more  or  less 


INTRODUCTION.  3 

definite  sphere  of  plienomena.  Thus  we  shall  consider  psychology 
as  that  science  which  has  for  its  primary  subject  of  investigation  all 
the  phenomena  of  human  consciousness,  or  of  the  sentient  life  of 
man.  If  the  term  "  sentience  "  be  employed  as  preferable  to  con- 
sciousness, it  must  be  understood  as  equivalent  to  consciousness  in 
the  broader  sense  of  the  latter  word.  This  definition,  or  rather  de- 
scription, plainly  implies  an  acquaintance  experimentally  with  cer- 
tain phenomena  that  cannot,  strictly  speaking,  be  defined.  These 
are  the  phenomena  of  consciousness  ;  and  one  result  of  all  our  sub- 
sequent investigations  will  be  to  show  us  that  consciousness  and 
its  primary  phenomena  can  never  be  defined.  The  definition  of 
psychology  need  not,  however,  be  understood  to  imply  the  real 
existence  of  any  one  entity  such  as  a  soul. 

Nevertheless  it  would  be  very  inconvenient,  not  to  say  impos- 
sible, to  begin  and  continue  the  investigation  of  psychical  phenom- 
ena, using  only  roundabout  phrases  through  fear  of  implying  the 
real  existence  of  some  spiritual  entity  called  the  Soul  or  the  Mind. 
In  some  sort  there  cannot  be  any  description,  much  less  any  scien- 
tific study,  of  the  phenomena  of  consciousness  without  implying 
somewhat  which  requires  us  to  use  a  word  like  these.  In  all  lan- 
guages, and  in  the  constant  everyday  use  of  them  all,  men  in  stating 
and  describing  the  phenomena  of  their  own  sentient  life  employ 
such  terms  as  "I"  and  "me,"  and  place  in  a  kind  of  contrast  with 
them  such  other  terms  as  " thou "  and  "  he  "  or  "it."  Inasmuch 
as  recollection,  and  the  assumption  of  some  kind  of  continuous 
personal  identity,  enter  into  all  their  experience,  and  underlie  all 
their  relations  with  each  other  and  with  the  physical  world  which 
surrounds  them,  they  are  compelled  to  use  language  implying  a 
permanent  subject  of  the  phenomena  of  consciousness.  No  one 
doubts  as  to  his  right  to  ascribe  to  himself  the  phenomena  of  his 
own  consciousness ;  and  as  well  to  ascribe  certain  other  phenom- 
ena, which  are  not  attributed  to  himself  as  their  subject,  to  other 
subjects  (so-called  "  persons  "),  which  he  supposes  to  have,  each  one, 
a  consciousness  of  his  own.  No  one  doubts  that  this  subject  is  in 
every  case  somehow  the  same  with  itself  from  hour  to  hour  and  day 
to  day,  and  even  from  year  to  year.  In  all  the  earlier  part  of  this 
treatise  the  word  "mind"  will  be  employed  simply  as  the  equiva- 
lent of  the  subject  (which  all  language  as  expressive  of  universal 
experience  necessarily  recognizes)  of  the  phenomena  of  conscious- 
ness. In  other  words,  whatever  all  men  inevitably  mean  by  the 
word  "I"  (the  empirical  ego  of  philosophy),  whenever  they  say  / 
think,  or  feel,  or  intend  this  or  that ;  and  whatever  they  under- 
stand others  to  mean  by  using  similar  language — thus  much,  and 


4  INTRODUCTION. 

no  more,  we  propose  at  first  to  include  under  the  term  "mind." 
This  term  is  preferred  to  the  word  "soul,"  in  part  out  of  concession 
to  the  prejudices  to  which  allusion  has  already  been  made,  and  in 
part  because  it  seems  to  admit  of  the  handling  which  it  is  proposed 
to  give  to  it  subsequently,  with  more  freedom  from  entangling  alli- 
ances with  ethical,  social,  aad  religious  ideas.  In  other  words,  we 
wish  to  begin  and  continue  as  far  as  possible  upon  purely  scientific 
grounds.  And  when,  subsequently,  these  grounds  are  in  part  aban- 
doned for  certain  fields  of  rational  speculation,  we  wish  to  have  the 
connection  between  the  two  kept  open  and  unimpeded. 

§  3.  In  accordance  with  what  has  already  been  said  concerning 
the  nature  of  psychology,  Ave  may  define  Physiological  Psychology 
as  the  science  which  investigates  the  phenomena  of  human  con- 
sciousness from  the  "  physiological  "  point  of  view  or  method  of 
approach.  Remembering  the  cautions  which  have  akeady  been 
expressed,  we  may  also  say  that  it  is  the  science  of  the  human  mind 
as  investigated  by  means  of  its  relations  to  the  human  physical  or- 
ganism. A  more  accurate  definition,  however,  requires  that  some- 
thing further  should  be  said  concerning  the  nature  and  method  of 
that  science  which  furnishes  the  adjective  to  our  compound  term. 
Human  Physiology  is  the  science  of  the  functions  (or  modes  of  the 
behavior  in  its  correlated  action)  of  the  human  physical  organism. 
As  studied  at  present  it  implies  an  acquaintance  with  the  fields  of 
gross  and  special  microscopic  anatomy  (histology),  of  embryology 
and  the  general  doctrine  of  development,  of  biology, — including  the 
allied  phenomena  of  plant  life, — of  molecular  physics  and  chemistry 
as  related  to  the  structure  and  action  of  the  bodily  tissues,  and  of 
other  forms  of  kindred  knowledge.  It  is  only  a  relatively  small  part 
of  this  vast  domain,  however,  with  which  Physiological  Psychology 
has  directly  to  deal ;  for  it  is  only  a  part  of  the  human  organism 
which  has  any  direct  relation  to  the  phenomena  of  consciousness. 
As  will  appear  subsequently,  it  is  with  the  nervous  system  alone, 
that  our  science  has  its  chief  immediate  concern.  Indeed  it  might 
be  described — though  in  a  stiU  somewhat  indefinite,  but  more  full 
and  complete,  way — as  the  science  which  investigates  the  correla- 
tions that  exist  between  the  structure  and  functions  of  the  human 
nervous  mechanism  and  the  phenomena  of  consciousness,  and  which 
derives  therefi'om  conclusions  as  to  the  laws  and  nature  of  the 
mind. 

§  4.  Physiology  is  compelled,  from  its  very  nature  as  a  physical 
science,  to  regard  the  nervous  system  as  a  mechanism.  Physiological 
Psychology,  inasmuch  as  it  relies  so  largely  upon  physiology  for  its 
data  and  method  and  points  of  view,  is  also  required  to  consider 


IlSrTRODTJCTION".  5 

this  system  in  the  same  way.  Those  unique  relations  in  which  the 
structure  and  functions  of  the  nervous  substance  of  the  body  stand 
to  the  phenomena  of  the  mind  cannot  deter  the  investigator  from  as- 
s)iming  toward  it  the  so-called  mechanical  point  of  view.  Physiology 
presents  psychology  with  a  description  of  this  nervous  substance  as 
a  vast  and  complex  system  of  material  molecules,  which  are  acted 
upon  by  different  forms  of  the  energy  of  nature  outside  (external 
stimuli),  and  by  intimate  changes  in  the  contiguous  molecules  of 
the  other  substances  of  the  body  (internal  stimuli)  ;  and  which  be- 
have as  they  do  on  account  of  the  influences  thus  received,  as  well 
as  on  account  of  their  own  molecular  constitution  and  arrangement. 
But  all  this  is  the  description  of  a  material  mechanism.  The  word 
"mechanism "is  preferable  to  the  word  "machine"  for  describing 
such  a  system  of  interacting  molecules  as  constitute  the  living  ner- 
vous substance,  because  we  attach  to  the  latter  word  the  mental  pict- 
ure of  something  which  has  a  certain  magnitude  and  rigidity  of 
parts  that  act  and  react  upon  each  other  in  a  palpable  way  under 
the  ordinary  laws  of  mechanics.  A  steam-engine  is  a  machine 
whose  parts  may  be  seen  to  push  and  pull  and  turn  each  other  after 
the  ordinary  fashion  of  all  levers  and  wheels.  But  the  molecules 
of  the  steam,  from  the  activity  of  which  all  the  motion  of  the  rigid 
and  ponderous  parts  of  this  machine  is  derived,  are  no  less  mate- 
rial and  governed  by  physical  law  in  their  changing  relations  to 
each  other  than  are  the  masses  of  the  machine  itself.  The  inter- 
action of  the  minute  particles  of  the  steam  falls  more  fitly,  how- 
ever, under  the  conception  of  mechanism.  Indeed,  it  is  only  as 
falling  under  this  general  conception  that  these  molecules  admit  of 
any  scientific  treatment  at  all.  Now  it  is  not  our  purpose  to  begin 
the  consideration  of  the  human  nervous  system  by  debating  the 
question,  how  completely  it  falls  under  the  conception  of  mechan- 
ism, and  whether  some  other  conception  be  not  needed  to  supple- 
ment this  when  the  unique  relations  of  this  system  to  the  phenomena 
of  the  mind  are  taken  into  account.  Whatever  is  to  be  said  upon 
such  a  question  must  appear  in  its  proper  place  in  the  order  adopted 
for  the  discussion  of  the  general  subject.  Physiological  Psychology, 
however,  can  scarcely  establish  itself  at  all  unless  it  be  willing  to 
receive  from  the  proper  one  of  the  two  sciences  which  enter  into  it 
that  conception  of  the  nervous  system  at  which  this  science  has 
arrived  as  the  result  of  the  most  successful  modern  researches.  As 
far  as  the  nervous  system  admits  of  being  subjected  at  all  to  scientific 
treatment,  for  the  purpose  of  attaining  a  more  complete  knowledge 
of  the  nature  of  its  functions,  it  is  necessarily  considered  as  a  com- 
plex molecular  mechanism.     We  shall,  then,  receive,  in  a  grateful 


6  IlSiTRODUCTION. 

and  docile  manner,  all  tliat  the  noble  science  of  human  physiology 
has  to  teach  us,  under  the  guidance  of  the  conception  of  a  mech- 
anism, both  directly  concerning  the  manner  in  which  the  nervous 
matter  of  the  human  body  performs  its  wonderful  functions,  and 
more  indirectly  concerning  the  relations  in  which  these  functions 
stand  to  the  phenomena  of  consciousness. 

§  5.  Physiological  Psychology — it  is  by  this  time  apparent — par- 
takes of  the  nature  and  methods  of  two  sciences  that  differ  widely 
from  each  other.  One  is  a  science  which  involves  introspection  ; 
for  it  is  only  by  the  method  of  introspection  that  the  real  and  pres-^ 
ent  facts  of  human  consciousness  can  be  reached.  The  other  is  a 
physical  science,  and  involves  external  observation  to  determine  the 
external  facts  of  the  structure,  development,  and  functions  of  a 
physical  mechanism.  Two  sets  of  phenomena  must  then  be  exam- 
ined in  their  relations  to  each  other,  and,  so  far  as  possible,  the 
laws  (or  permanent  modes)  of  these  relations  pointed  out.  It  is 
due  to  this  fact,  in  part,  that  both  the  peculiar  difficulties  and  the 
peculiar  interest  and  value  of  psycho-physical  researches  are  so 
great. 

In  every  science  a  beginning  is  first  made  by  ascertaining  and 
comparing  together  all  the  important  phenomena  ;  the  laws,  or 
regular  modes  of  the  occurrence  of  the  phenomena  in  relation  to 
each  other,  are  then  investigated  ;  and,  finally,  certain  conclusions 
are  drawn  concerning  the  nature  and  significance  of  those  real  be- 
ings which  reason  compels  us  to  assume  as  permanent  subjects  of 
the  different  classes  of  phenomena.  In  its  effort  to  establish  itself 
upon  a  scientific  basis.  Physiological  Psychology  has  no  choice  but 
to  follow  essentially  the  sarce  method  of  procedure.  In  its  case, 
however,  as  has  already  been  remarked,  the  phenomena  which  are 
to  be  ascertained  and  compan  d  belong  to  two  orders  that  obviously 
differ  greatly  from  each  other  ;  and  the  laws  which  it  is  sought  to 
discover  ai'e  laws  which  maintain  themselves  between  these  two  or- 
ders of  phenomena.  The  phenomena  of  the  nervous  system,  like 
all  physical  phenomena,  consist  in  changes  in  the  constitution  and 
mutual  relation  of  material  masses  and  molecules.  They  are,  then, 
of  a  kind  to  be  related  to  each  other,  under  the  conception  of  mech- 
anism, inside  of  the  nervous  system  and  of  the  entire  human  body  ; 
and  also,  outside  of  the  body,  to  the  various  forms  of  physical  energy 
in  nature  which  act  upon  these  masses  and  molecules.  But  the 
psychical  jDhenomena  are  states  of  consciousness,  constantly  shifting 
modes  of  the  behavior  of  that  subject  which  Ave  have  agreed — as 
much  as  possible  without  involving  any  j^remature  assumptions — to 
call  the  Mind.     Still  the  above-mentioned  two  orders  of  phenomena 


IlsrTKODUCTION".  7 

are  obviously  to  a  large  extent  related  to  each  other  ;  they  may,  in 
fact,  be  said  to  be  correlated  in  a  unique  manner.  The  constant 
forms  of  this  correlation  constitute  the  laws  for  the  discovery  of 
which  Physiological  Psychology  undertakes  its  special  researches. 
It  endeavors  to  bring  the  two  orders  of  phenomena  face  to  face,  to 
look  at  them  as  they  stand  thus  related  to  each  other,  and,  as  far  as 
possible,  to  unite  them  in  terms  of  a  uniform  character,  under  law. 
It  might  seem  that  simjDly  to  attempt  the  accomplishment  of  the 
task  just  described  should  satisfy  all  legitimate  demands.  And, 
indeed,  no  little  protest  has  of  late  been  made  against  any  attempt 
on  the  part  of  scientific  psychology  (and  how  much  more  when 
studied  from  the  physiological  and  experimental  point  of  view)  to 
proceed  further  than  this.  All  inquirers  have  been  warned,  not  only 
against  introducing  metaphysical  assumptions  into  the  beginnings 
of  psychology,  but  also  against  allowing  any  admixtui'e  of  the  two 
during  the  investigations  pursued  by  the  latter.  We  have,  indeed, 
just  agreed  that  metaphysical  assumptions  as  to  the  natui-e  of  mind 
should  prejudice  as  Httle  as  possible  our  statement  of  psychological 
facts  and  laws.  But  if  the  warning  against  so-called  "  metaphysics  " 
be  understood  to  mean  that  inquiry  must  be  stopped  when  the 
phenomena  and  their  uniform  modes  of  relation  have  been  enume- 
rated, and  that  no  venture  must  be  made  upon  any  discussions  or 
conclusions  regarding  the  real  nature  of  the  subject  of  them  all 
(the  mind),  such  warning  may  very  weU  be  quietly  disregarded. 
What  we  are  chiefly  interested  in,  on  undertaking  aU  josychological 
investigation,  is  the  real  nature — the  permanent  characteristics,  the 
claims  to  be  a  substantial  existence,  a  spiritual  unity — and  the  ori- 
gin and  destiny  of  the  mind.  To  assume  as  little  as  possible  con- 
cerning all  this,  at  the  first,  is  simply  a  matter  of  wise  reserve  and 
self-control  in  the  interests  of  scientific  investigation.  We  feel  no 
hesitancy,  however,  in  announcing  our  intention,  ultimately,  to 
draw  whatever  conclusions  seem  to  us  legitimate  and  desirable  con- 
cerning many  of  these  so-caUed  "metaphysical"  inquiries.  Psy- 
chology— no  less  truly  when  studied  from  the  physiological  and  ex- 
perimental point  of  view — has  the  undoubted  right,  and  is  under 
the  obhgation,  to  contribute  as  much  as  possible  toward  the  solu- 
tion of  these  inquiries.  Nor  do  observation  and  wide  reading 
show  that  the  advocates  of  "  psychology  without  a  soul,"  and  freed 
from  all  metaphysics,  are  at  all  certain  to  avoid  drawing  con- 
clusions, not  to  say  introducing  illegitimate  assumptions,  upon 
these  very  same  inquiries.  In  brief,  Physiological  Psychology  has 
the  right,  which  belongs  to  it  as  a  science,  to  introduce  whatever 
conclusions  as  to  the  natiire  of  mind  follow  legitimately  from  its 


8  INTRODUCTION. 

discussions  of  plienomena  and  laws.  It  has  even  a  right  to  in. 
dulge  in  well-founded  and  reasonable  speculation.  Such  things  are 
not  necessarily  objectionable  when  indulged  in  by  any  of  the  more 
purely  physical  sciences.  Indeed,  there  is  not  one  of  these  sciences 
which  would  not  look  comparatively  bare  and  unattractive  if  wholly 
stripped  of  its  more  or  less  questionable  inferences,  its  metaphysi- 
cal assumptions,  its  guessings,  and  speculations. 

§  6.  The  remai'ks  immediately  foregoing  serve  to  indicate  what 
are  the  principal  Divisions  of  this  work.  The  Fii'st  Part  will 
consist  of  a  description  of  the  structure  and  functions  of  the  Ner- 
vous System.  This  system  will  there  be  considered  tmder  the 
conception  of  a  mechanism,  and  as  far  as  possible  without  any 
direct  or  indirect  reference  to  the  phenomena  of  consciousness  as 
determined  by  introspection.  The  Second  Part  will  describe  the 
various  classes  of  correlations  which  exist  between  the  phenomena 
of  the  nei'vous  mechanism  and  mental  phenomena.  It  will  also 
attempt  to  state  what  is  known  of  the  laws  which  maintain 
themselves  over  these  various  classes.  No  attempt  will  be  made, 
however,  to  describe  and  discuss  any  of  the  phenomena  which  may 
be  classed  as  abnormal,  or  as  consisting  (so  far  as  they  are  psychical) 
in  so-called  "  disturbances  of  consciousness,"  except  when  reference 
to  such  abnormal  phenomena  is  necessary  in  order  to  explain  those 
which  are  called  ordinary  or  normal.  The  phenomena  of  insanity, 
delirium,  hypnotism,  somnambulism,  ecstasy,  mind-reading,  spir- 
itualism, and  even  of  sleep  and  dreaming,  will  therefore  be  defi- 
nitely excluded.  The  chief  reason  for  such  exclusion  is  to  be  found 
in  a  lack  of  space,  it  being  difl&cult  even  to  bring  within  the  limits 
of  a  single  volume  a  sufficiently  thorough  discussion  of  the  more 
ordinary  phenomena  with  which  Physiological  Psychology  is  caUed 
upon  to  deal. 

The  various  correlations  of  the  mind  and  the  nervous  mechanism 
(of  which  the  Second  Part  treats)  may  be  conveniently  consid- 
ered under  several  principal  groups  or  classes.  The  first  of  these 
includes  more  particularly  such  relations  as  can  be  established  be- 
tween the  condition  and  activity  of  the  supreme  nei-vous  centres 
and  the  phenomena  of  conscious  sensation  and  voUtion.  Most  of 
what  can  be  said  at  present  upon  this  point  may  be  summed  up  in 
the  discussion  of  the  localization  of  cerebral  function,  as  taken  in 
connection  with  the  description  of  the  automatic  and  reflex  action  of 
these  centres  considered  as  parts  of  the  nervous  mechanism.  The 
second  class  of  these  correlations  covers  all  the  phenomena  with 
whifh  psycho-physics  (in  the  more  precise  use  of  the  term)  attempts 
to  deal.    It- discusses  the  relations  which  exist  between  the  quality, 


INTKODUGTIOI^".  9 

quantity,  combination,  and  order  of  succession  in  time,  of  the  vari- 
ous stimuli  which  act  upon  the  nervous  system,  and  the  kind,  mag- 
nitude, composite  result,  and  time-relations  of  the  mental  phe- 
nomena. Hence  the  significance  of  the  term  psycho-physics.  As 
Physiological  Psychology  is  ordinarily  and  legitimately  treated, 
it  includes  these  more  specially  psycho-physical  researches.  An- 
other class  of  these  correlations  covers  certain  related  phenomena 
of  mind  and  body  as  dependent  upon  age,  sex,  race,  etc. 

Besides  the  foregoing  groups,  or  classes,  certain  observations 
which  have  more  or  less  of  scientific  confirmation  and  value, 
may  be  made  regarding  the  physical  basis  of  the  feelings  and  voli- 
tions controlling  the  bodily  members,  and  of  the  higher  faculties  of 
memory,  association  of  ideas,  etc.  The  Third  Part  will  fitly  intro- 
duce, at  the  close  of  the  psycho-physical  researches,  the  presenta- 
tion of  such  conclusions  as  may  be  legitimately  gathered,  or  more 
speculatively  inferred,  concerning  the  nature  (considered  as  a  real 
being)  of  the  human  mind.  The  justification  of  the  order  and  ex- 
tent of  the  entire  discussion,  and  especially  of  the  Third  Part  as  a 
whole,  has  already  been  given  to  some  extent ;  the  rest  must  be 
left  to  the  progress  and  result  of  the  discussion  itself. 

§  7.  It  has  already  been  said  that  the  peculiarity  of  Physiological 
Psychology,  considered  as  a  branch  of  the  general  science  of  mind, 
consists  largely  in  the  method  of  its  approach  to  its  subject.  At- 
tention must  now  be  more  specifically  called  to  this  method  as 
necessarily  partaking  of  the  methods  of  the  two  sciences  whose 
researches  it  undertakes  to  combine.  The  method  of  physiology, 
which  is  in  general  that  of  external  observation  as  employed  in  all 
the  physical  sciences,  should  be  applied  only  when  supplemented  by 
the  many  delicate  and  accurate  instruments  of  observation  now  at 
command,  and  guarded  and  checked  by  that  accumulation  of  expe- 
rience concerning  the  best  ways  of  studying  nature  and  concern- 
ing her  ways  of  working  which  the  whole  body  of  such  sciences 
has  made.  On  the  other  hand,  the  method  of  psychology  has  or- 
dinarily been  defined  as  solely  the  method  of  introspection  or  self- 
consciousness.  These  two  methods  are  obviously  very  different. 
It  would  not  be  strange,  then,  if  the  science  which  finds  it  neces- 
sary to  combine  the  two  should  experience  some  special  difficulty. 
This  difficulty  has,  however,  more  often  been  exaggerated  than  ex- 
plained and  (what  is  quite  possible)  for  the  most  part  removed. 

Our  present  purpose  does  not  require  that  we  should  examine  at 
length  the  question  whether  the  introspective  method  is  the  only 
one  possible  in  psychology.  Scarcely  moi-e  is  necessary  than  the 
statement  of  the  bearing  of  this  question  upon  the  inquiries  it 


10  INTKODUCTION. 

is  proposed  to  make.  There  should  in  general  be  no  mystery  or 
arrogant  assumption' about  the  use  of  such  words  as  "science"  and 
"scientific  method."  Science  is  nothing  but  knowledge — real,  veri- 
fiable, and  systematic.  Scientific  method  is  nothing  but  the  way 
of  arriving  at  such  knowledge.  Now,  although  Physiological  Psy- 
chology brings  the  investigator  face  to  face  with  some  of  the  most 
interesting  and  distinctive  mysteries,  it  is  not,  as  a  science,  to  be 
regarded  as  especially  mysterious.  Inasmuch  as  its  specific  busi- 
ness is  to  ascertain  and  combine,  under  definite  laws,  two  widely 
differing  classes  of  facts  (facts  of  the  human  nervous  mechanism  and 
facts  of  human  consciousness)  it  is,  of  course,  compelled,  first  of  all, 
to  ascertain  both  kinds  of  facts.  The  phenomena  of  consciousness, 
as  primary  facts,  can  be  ascerlained  in  no  other  way  than  in  and  by 
consciousness  itself.  Whatever  fault  may  be  found  with  the  so- 
called  introspective  method  in  psychology,  on  account  of  its  alleged 
inaccuracy,  lack  of  scientific  and  progressive  quality,  etc,  from  the 
very  natui'e  of  the  case  no  other  way  of  ascertaining  what  the  phe- 
nomena of  consciousness  in  themselves  are  can  ever  take  the  place 
of  the  dii'ect  examination  of  consciousness.  And  there  is  no  way  of 
directly  examining  consciousness  but  the  way  of  being  conscious 
one's  self.  On  the  other  hand,  it  is  perfectly  obvious  to  students 
of  psychology  and  of  its  history  (on  grounds  which  need  not  be 
stated  here)  that  the  scientific  treatment  of  the  facts  of  conscious- 
ness can  never  be,  to  any  satisfactory  extent,  accomplished  by  in- 
trospection alone.  For  psychology,  in  order  to  make  valid  its  claim 
to  be  a  science,  must  not  merely  display  the  alleged  facts  of  individ- 
ual mental  expex'ience  ;  it  must  treat  these  facts  analytically,  must 
resolve  them  into  their  ultimate  factors,  and  trace  the  stages  of 
their  development  from  what  is  simpler  to  what  is  more  complex  ; 
it  must  also  show  on  all  sides  their  connections  and  causes,  thus 
placing  the  phenomena  of  the  mind  as  much  as  possible  in  interac- 
tion with  the  rest  of  the  world.  It  is  because  human  physiology  can 
contribute  largely  to  such  scientific  treatment  (as  distinguished  from 
the  mere  observation,  grouping,  and  cataloguing)  of  the  phenomena 
of  the  mind  that  it  is  entitled  to  be  considered  as  furnishing  one 
distinctive  and  fruitful  branch  of  psychological  researches. 

§  8.  The  following  statements  will,  accordingly,  be  found  to  hold 
good  concerning  the  method  of  Physiological  Psychology.  It  must 
employ  faithfully  the  methods  distinctive  of  both  the  two  sciences 
which  it  endeavors  to  combine.  Facts  as  to  the  structure  and 
functions  of  the  nervous  mechanism,  and  as  to  the  effect  upon  it  of 
various  kinds  of  physical  energy  acting  as  stimuli,  must  be  ascer- 
tained by  external  observation.     In  general  they  must  be  accepted 


INTEODUCTION.  11 

by  us  as  contributed  from  the  modern  science  of  human  physiology. 
The  primary  facts  of  consciousness  must  be  ascertained  from  con- 
sciousness itself ;  or,  since  they  have  already  been  for  a  long  time 
subjected  to  this  form  of  observation,  and  tabulated,  compared,  and 
classified,  they  may  be  accepted  from  the  science  of  introsjjective 
psychology.  Care  must  be  taken,  however,  to  make  sure  that  all 
alleged  psychical  facts  are  really  facts  ;  but  iipon  this  point,  again, 
there  is  no  other  way  of  making  sure  than  in  and  through  conscious- 
ness. The  principal  laws  and  inferences  also  of  introspective  psy- 
chology may  be  accepted  (at  least  in  a  provisional  way)  on  begin- 
ning the  study  of  Physiological  Psychology.  The  final  result  of 
such  study  will  doubtless  be,  not  only  to  sujDplement  and  explain, 
but  also  to  modify  and  correct,  the  statement  of  these  laws  and  in- 
ferences. But  here,  as  in  other  scientific  research,  we  are  obliged 
to  work  our  way  through  many  mistakes,  obscurities,  and  other  ob- 
stacles, progressively  nearer  the  complete  and  verifiable  knowledge 
of  the  truth. 

Furthermore,  from  the  nature  of  the  case.  Physiological  Psychol- 
ogy takes  its  point  of  starting  from  the  facts  and  laws  of  physiology 
as  reached  by  the  method  of  external  observation.  This  follows 
necessarily  from  the  relation  in  which  the  two  sciences  of  physiol- 
ogy and  psychology  stand  as  entering  into  the  proposed  combina- 
tion. The  enlargement  of  our  knowledge  of  the  latter  is  the 
end  to  be  reached  ;  but  the  former  is  to  give  us  the  way  by  which, 
and  the  guidance  under  which,  the  approach  to  this  end  must  be 
made. 

It  will  also  become  evident,  in  the  course  of  the  following  inves- 
tigation, that  we  are  seldom  or  never  able  to  proceed  directly  with 
the  work  of  comparing  the  immediate  physical  antecedents  or  con- 
sequents of  the  mental  phenomena  with  these  phenomena  them- 
selves, and  so  of  drawing  conclusions  at  once  as  to  the  laws  by 
which  the  two  classes  of  facts  are  connected.  Such  immediate  an- 
tecedents and  consequents  are  hid  in  the  inexplorable  recesses  of 
the  living  and  molecularly  active  brain.  It  is  seldom,  indeed,  that 
our  direct  observation  can  approach  within  the  tenth,  or  it  may  be 
within  the  hundredth,  remove  of  what  goes  on  in  these  recesses.  We 
are  obliged  to  examine  the  physical  phenomena  from  a  greater  dis- 
tance and  in  a  more  indirect  way.  For  example,  physics  can  inform 
us  what  combinations  of  what  wave-lengths  of  the  vibration  of  ether 
fall  on  the  eye  when  a  certain  form  of  conscious  sensation,  which 
we  call  "  yellow  "  or  "  red  "  or  "  blue  "  arises  ;  physiology  can  lo- 
cate the  nervous  elements  of  the  retina  upon  which  the  waves  fall, 
can  conjecture  something  as  to  the  chemical  changes  there  produced, 


12  INTEODUCTIOlSr. 

and  trace  doubtfully  the  paths  along  which  the  resulting  nervous 
impulses  rise  to  the  brain  and  diffuse  themselves  over  certain  of 
its  areas  ;  psycho-physics  can  tell  approximately  the  relatious  in 
which  the  varying  quantities  of  the  stimulus  stand  to  the  resulting 
degrees  of  the  sensations.  But  in  all  this  we  are  still  at  a  great  dis- 
tance from  the  enjoyment  of  those  opportunities  which  would  seem 
necessaiy  to  make  the  science  of  Physiological  Psychology  as  com- 
prehensive and  exact  as  could  readily  be  wished.  As  a  rule,  certain 
kinds  and  amounts  of  physical  energy,  more  or  less  definitely  meas- 
urable, are  known  to  be  acting  on  the  peripheral  parts  of  the  body, 
and  the  next  series  of  observed  facts  is  the  emergence  in  conscious- 
ness of  a  psychical  experience  quite  unlike  all  kinds  of  physical  en- 
ei'gy.  To  be  sure,  Fechner's  '  conception  of  psycho-physics  is  that 
it  treats  those  "physical  activities  which  are  the  bearers  {Trdger)  or 
conditions  of  the  psychical,  and  accordingly  stand  in  direct  func- 
tional relation  with  them  ;"  or  again,  "psycho-physics  is  an  exact 
doctrine  of  the  relations  of  function  or  dependence  between  body 
and  soul — of  the  universals  that  lie  between  the  bodily  and  spirit- 
ual, the  physical  and  psychical  world."  But  it  will  be  seen  that  of 
such  physical  activities  we  have  little  or  no  assured  knowledge  ;  al- 
though we  have  the  best  of  grounds  for  believing  that  such  activities 
exist,  and  that  they  stand  in  important  relations  under  law  with  the 
facts  of  the  conscious  psychical  life. 

It  follows,  then,  that  Physiological  Psychology  is,  pre-eminently, 
first  experimental  and  then  speculative ;  it  can  never  become 
strictly  demonstrative,  or  even  deductive  to  any  considerable  ex- 
tent. That  a  strictly  demonstrative  science  of  the  relations  be- 
tween the  structure  and  functions  of  the  nervous  mechanism  and 
the  phenomena  of  consciousness  is  impossible,  we  might  argue  from 
the  most  ordinary  experience.  To  infer  from  certain  movements 
of  material  molecules  that  certain  facts  of  consciousness  munt  take 
place,  under  the  most  universal  laws  of  all  Being,  involves  a  kind 
and  amount  of  knowledge  of  which  we  cannot  even  clearly  conceive. 

In  brief,  our  proper  course  will  be,  first,  to  explain,  as  completely 
as  possible,  the  structure  and  functions  of  the  nervous  mechanism  ; 
and  then  to  set  forth,  as  fully  as  the  present  means  at  disposal  will 
permit,  the  various  relations  in  which  its  action  under  stimuli 
stand  to  the  phenomena  of  the  mind.  In  attempting  the  latter 
problem  we  shall  come  upon  a  few,  but  only  a  few,  general  state- 
ments of  fact  which  deserve  to  be  s^ooken  of  as  laws  in  any  strict 
meaning  of  the  word. 

1  Elemente  d.  Psychophysik,  pp.  8  and  10.     Leipzig,  1860. 


INTRODUCTIOlSr.  13 

§  9.  If  the  correctness  of  the  remarks  last  made  be  admitted,  the 
inquiry  may  be  raised  :  What  justification  has  this  so-called  sci- 
ence of  Physiological  Psychology  for  the  large  claims  which  it  has 
made  of  late  ;  and,  indeed,  what  right  has  it  to  exist  as  a  special 
discipline  at  all?  The  full  answer  to  the  call  for  self-justification 
must  be  made  by  the  actual  achievements  of  the  science  itself.  It 
will  be  better,  then,  to  leave  it  to  the  convictions  of  the  reader  when 
the  presentation  of  these  achievements  shall  have  been  made.  But 
even  at  this  point  an  appeal  may  be  taken  to  certain  facts.  We 
have  already  repeatedly  conceded  the  fact  that  we  are  to  investigate 
the  phenomena  of  consciousness  (that  is,  study  psychology)  by  a 
special  method  rather  than  try  to  establish  an  independent  science 
or  even  separate  branch  of  the  general  science  of  mind.  The  de- 
mand for  a  justification  is  then  reduced  to  this — Is  there  valid 
reason  for  studying  psychology  in  this  particular  way  ;  for  approach- 
ing its  domain  through  the  researches  and  conclusions  of  physi- 
ology ?  To  such  a  question  there  can  be  but  one  intelligent  answer. 
There  is  an  abundance  of  valid  reason. 

The  history  of  modern  investigation,  and  the  conclusions  of  the 
modern  science  of  man,  both  physical  and  psychological,  emphasize 
the  necessity  of  studying  his  nature  and  development  as  that  of  a 
living  unity.  Such  science  shows  man  to  be  at  the  head  of  a  series 
of  physical  and  psychical  existences  ;  he  cannot  be  understood  as 
he  is,  in  his  whole  nature  and  in  his  place  within  nature  at  large, 
without  taking  both  sides  of  this  living  unity  into  account.  For 
man  is  known  to  himself  as  body  and  mind — and  not  as  bodiless 
spirit  or  a  mindless  congeries  of  moving  molecules.  That  the  struct- 
ure and  functions  of  the  body,  especially  of  the  nervous  mechan- 
ism, and  the  activities  of  the  mind,  are  extensively  and  intimately 
correlated,  is  a  fact  beyond  all  doubt.  It  is  the  particular  task  of 
Physiological  Psychology  to  show  in  what  manner,  and  to  what  ex- 
tent, such  correlation  exists.  Moreover,  there  are  few  questions 
more  interesting,  from  a  philosophical  and  an  ethical  point  of  view, 
than  such  as  the  following  :  What  is  the  nature  of  mind,  considered 
in  the  light  of  its  correlations  with  the  body  ?  and.  Do  the  so-called 
physiological  and  the  so-called  psychical  phenomena  belong  to  one 
subject,  or  to  more  than  one?  But  these  and  similar  questions 
can  be  scientifically  answered  only  by  giving  a  speculative  treat- 
ment to  the  conclusions  of  psycho-physical  investigation. 

In  brief,  it  may  be  said  that  introspective  psychology,  important 
as  its  results  have  been,  and  indispensable  as  its  method  is,  has 
shown  its  incompetency  to  deal  with  many  of  the  most  interesting 
inquiries  which  it  has  itself  raised.     On  the  other  hand,  psychology 


14  INTKODUCTIOW. 

as  pursued  by  tlie  experimental  and  physiological  method  has  al- 
ready thi'own  a  flood  of  fresh  light  upon  many  of  these  inquiries. 
We  may  affirm  with  Wundt,'  without  fear  of  successful  contradic- 
tion :  "Psychology  is  compelled  to  make  use  of  objective  changes 
in  order,  by  means  of  the  influences  which  they  exert  on  our  con- 
sciousness, to  establish  the  subjective  properties  and  laws  of  that 
consciousness."  On  this  fact  and  on  th§  real  achievements  of  the 
method  we  confidently  rest  its  claims  to  serious  and  permanent  con- 
sideration. 

'  Art.   "Ueber  psychophysiken  Methoden,"  Philosophisclie  Studien,  1881, 
heft  1,  p.  4. 


PART   FIRST. 


THE  NERYOUS  MECHANISM. 


CHAPTER  I. 
THE  ELEMENTS  OF  THE  NEEVOUS  SYSTEM. 

§  1.  In  all  forms  of  animal  life,  except  the  very  lowest,  the  pres- 
ence and  activity  of  a  nervous  system  constitutes  the  chief  charac- 
teristic of  their  difference  from  all  the  more  nearly  corresponding 
forms  of  plant  life.  Both  animals  and  plants  are  organisms,  and 
their  structure — regarded  as  a  whole  composed  of  an  indefinite 
number  of  material  masses  or  particles,  which  move  with  reference 
to  each  other  for  the  accomplishment  of  a  common  piece  of  work 
— may  be  considered  as  a  "natural  mechanism."  Both  have  mate- 
rial parts  of  superior  firmness,  adapted  to  divide  off  and  to  support 
their  softer  parts.  Plants,  as  well  as  animals,  are  possessed  of  liv- 
ing, and,  more  especially,  of  contractile  tissue  ;  they  are  therefore 
capable  of  the  functions  of  nutrition,  of  propagation,  and  of  that 
so-called  automatic  motion  which  is  thought  to  be  a  fundamental 
property  of  protoplasm.  As  is  well  known,  science  is  not  yet  able 
always  to  distinguish  between  the  lowest  forms  of  animal  and  the 
lowest  forms  of  plant  life.  But  nervous  tissue  and  its  functions 
do  not  belong  to  the  vegetable  kingdom  ;  on  the  contrary,  the  pos- 
session and  use  of  at  least  a  rudimentary  mechanism  of  nerve-fibres 
and  nerve-cells  are  found  in  most  members  of  the  animal  kingdom. 

It  is  true  that,  even  in  the  case  of  animals  which  do  possess 
a  nervous  system,  the  structure  and  functions  of  the  nervous  tissue 
are  very  closely  related  to  those  of  the  merely  contractile  tissue. 
Thus  the  muscular  tissue  of  the  animal  might  seem  to  be  a  connect- 
ing-link between  its  own  nervous  tissue  and  the  contractile  tissue 
of  the  plant.  For  the  motor  nerves,  at  least,  are  anatomically  con- 
nected by  means  of  their  end-plates  with  the  contractile  substance 
of  the  muscular  fibre,  and  the  result  of  modern  experimentation, 
with  both  muscles  and  nerves,  has  been  to  make  clear  many  feat- 
ures of  resemblance  between  them.  On  the  other  hand,  even  the 
isolated  nervous  elements,  when  subjected  to  the  same  exjDeri- 
mental  tests  as  those  which  are  used  to  determine  the  funda- 
mental properties  of  contractile  tissue,  exhibit  certain  marked 
differences  of  behavior  ;  while  the  functions  of  such  elements, 
3 


IS  FUlSrCTION   OF   A   IS^ERVOUS   MECHANISM. 

when  combined  into  a  very  simple  nervous  system,  are  alto- 
gether unique.  Moreover,  as  the  nervous  system  of  the  animal 
becomes  more  elaborate  and  complex,  and  especially  as  its  central 
organs — spinal  cord  and  brain — are  relatively  developed,  other  new 
and  wonderful  functions  are  seen  to  be  connected  with  it.  In  the 
case  of  the  superior  vertebrate  animals,  and  especially  of  man,  the 
significance  of  this  particular  form  of  a  physical  mechanism  be- 
comes, therefore,  vastly  increased.  Thus  the  minute  structure  of 
the  nervous  mechanism  invites  the  student  of  chemistry,  molecular 
physics,  and  histology,  to  investigations  of  the  greatest  interest  and 
yet  of  extreme  difficulty  ;  while  the  functions  of  this  mechanism 
are  so  curiously  and  intimately  connected  with  the  phenomena,  not 
merely  of  all  higher  animal  life,  but  also  of  human  consciousness, 
that  inquiry  into  them  is,  among  all  physical  inquiries,  the  one  of 
unparalleled  intellectual  interest  and  importance. 

§  2.  It  will  be  the  work  of  this  entire  treatise  to  set  forth  in  some 
detail  the  unique  functions  of  the  human  nervous  mechanism,  to 
which  allusion  has  just  been  made.  For  the  present  a  very  gen- 
eral and  somewhat  indefinite  statement  of  these  functions  must  suf- 
fice. In  general,  and  somewhat  indefinitely,  it  may  be  said,  then, 
that  the  one  great  function  of  the  nervous  system  is  to  concatenate  (or 
link  together  into  a  whole)  the  manifold  elements,  both  physical  and 
psycho-physical,  which  enter  into  the  twofold  life  of  man.  Differ- 
ent and  distant  parts  of  the  body,  whether  they  belong  to  the  same 
or  to  different  so-called  systems  (as,  for  example,  the  circulatory, 
the  secretory,  the  digestive,  the  muscular),  are  bound  together,  and 
made  to  exercise  their  functions  in  reciprocal  dependence  and  for 
common  ends,  by  the  nervous  mechanism.  The  whole  body  is  also 
linked  to  the  external  world,  and  kept  in  either  unconscious  or  con- 
scious adjustment  to  the  changeful  play  of  its  forces,  by  the  same 
mechanism.  And  further,  the  development  of  the  mental  life,  at 
least  in  all  its  more  primitive  and  fundamental  factors,  is  mediated 
by  the  nervous  system.  For  it  is  certainly  in  connection  with  the 
exercise  of  nervous  functions  that  sensation  takes  place  ;  and,  by 
development  and  combination  of  the  sensations,  all  our  perceptions 
of  the  so-called  "  Things  "  of  the  external  world.  It  is  the  nervous 
mechanism  which  uiiites  the  entire  body  with  the  physical  stimuli 
of  tlie  external  world,  on  the  one  hand,  and,  on  the  other,  with  the 
primitive  activities  of  mind.  What  relation  the  nervous  functions 
have,  and  whether  they  have  any  direct  relation  at  all,  to  memory, 
judgment,  and  the  higher  activities  of  mind  in  general,  we  do  not 
now  even  inquire. 

The  significance  of  the  above-mentioned  function  of  "  concatena- 


.      EXAMPLES   OF   EEFLEX  ACTION".  19 

tion,"  so  far  as  it  concerns  the  different  and  distant  parts  of  the 
body,  might  be  illustrated  in  many  ways.  Inasmuch  as  the  plant 
is  an  organism,  there  is  a  reciprocal  dependence  of  the  structure 
and  action  of  all  its  parts.  But  each  part  of  the  plant  acts  directly 
and  slowly  on  only  contiguous  parts  in  effecting  the  distribution 
of  the  fluids,  upon  the  spread  of  which  the  life  and  growth  of  the 
plant  depend.  In  the  case  of  the  animal,  however,  an  effect  pro- 
duced in  one  part  of  the  body  may  quickly  spread  to  other  distant 
parts  by  the  mediation  of  the  nervous  system.  The  circulation  of 
the  blood  is  made  to  affect,  and  to  be  affected  by,  the  state  of  the 
skin  and  the  muscles,  the  state  of  the  respiratory  organs,  or  the 
state  of  the  mind's  feeling  as  determined  by  the  ideas  before  the 
mind.  A  draught  of  cold  air,  for  example,  strikes  some  peripheral 
portion  of  the  body  ;  the  heart  and  lungs  modify  their  activities, 
the  muscles  contract,  and  a  shudder  runs  through  the  physical 
framework  ;  the  secretions  are  disturbed,  and  the  mind  is,  perhaps, 
seized  with  a  vague  feeling  of  fear.  Such  a  complex  effect  of  the 
stimulus  of  cold  on  some  region  of  the  skin  has  been  brought  about 
by  the  action  of  the  nervous  system,  with  its  peripheral  end-organs, 
conducting  nerve-fibres,  and  nervous  centres.  Or,  again,  the  seeing 
of  some  sight  or  the  hearing  of  some  sound  is  followed  by  ideas  and 
emotions  of  shame,  or  of  fear,  or  of  joy.  A  complex  co-ordination 
of  the  muscles  then  takes  place,  so  as  to  move  the  limbs  in  running, 
to  give  or  ward  off  a  blow,  to  extend  the  hand  in  greeting,  to  lift 
up  or  bow  down  the  head.  In  this  case,  also,  the  action  of  heart 
and  lungs  and  secretory  organs  is  greatly  modified  ;  the  capillary 
circulation  is  altered,  and  the  cheeks  are  blanched  or  reddened  ; 
the  pupils  and  lachrymal  ducts  of  the  eyes  are  moved  ;  the  very 
hair  of  the  head  seems  to  sympathize  with  the  state  of  the  mind. 
Thus,  changes  which  involve  the  functions  of  almost  all  the  tissues 
and  organs  of  the  body  are  accomplished  by  the  mediation  of  the 
nervous  mechanism.  Unlike  the  modifications  in  expression  of 
function  which  take  place  in  the  plant,  they  are  accomplished  with 
what  seems  a  practical  instantaneousness.  The  complexity  of  the 
reciprocal  changes  which  characterize  the  life  of  the  higher  animals 
is  due  to  the  general  functions  of  the  nervous  system  ;  the  speed 
with  which  the  changes  are  accomplished  is  dependent  upon  the 
laws  of  the  propagation  of  nervous  impulses  within  that  system. 

Further  illustration  of  this  general  office  of  the  mechanism  of 
nerve-fibres  and  nerve-cells  in  "  concatenating "  the  manifold  ele- 
ments of  physical  and  psycho-physical  life  may  well  be  left  to  the 
progress  of  our  examination. 

§  3.  The  application  of  the  term  "  mechanism  "  to  the  nervous  sys- 


2;)  FUNCTION   OF  A   NERVOUS   MECHANISM. 

tern  of  man  has  already  (see  p.  4  £f.)  been  partially  explained  and 
justified.  We  now  describe  the  elementary  parts  of  such  a  system 
as  considered  from  the  same  general  point  of  view  which  induces 
us  to  aj^ply  this  term  to  the  structure  and  functions  of  the  entire 
system.  In  order  to  do  this,  it  is  necessary  to  speak,  first,  of  the 
structure,  and,  second,  of  the  function  of  these  parts,  regarded  as  the 
fundamental  and  distinguishing  factors  of  a  complex  mechanism. 
That  is  to  say,  two  inquiries  must  be  made  :  What  is  the  composi- 
tion and  form  of  those  ultimate  structures  called  nervous  elements, 
into  which  microscopic  anatomy  analyzes  the  nervous  system  ?  and, 
W^hat  can  such  stnictures  do  which  fits  them  to  act  as  parts  of  a 
"  mechanism  "  like  that  of  the  nervous  system  ?  It  is  obvious  that 
the  answers  to  these  inquiries  lie  at  the  very  entrance  upon  the 
way  toward  a  complete  science  of  the  nervous  mechanism.  But 
even  if  the  fullest  imaginable  answers  were  already  attained,  much 
would  remain  to  be  done  in  order  to  perfect  the  science.  Histology 
would  still  have  to  inform  us  precisely  how  the  elements  are  com- 
bined into  the  manifold  organs  of  a  system.  Physiology  would 
have  to  discover  the  laws  according  to  which  the  functions  of  the 
elements  are  modified,  when  they  act  as  thus  combined.  Of  course, 
to  know  completely  the  nature,  number,  and  properties  of  all  the 
individual  factors  of  a  mechanical  system,  and  to  know  also  pre- 
cisely how  those  factors  are  combined  into  the  system,  as  well  as 
how  their  modes  of  behavior  are  affected  by  such  a  combination, 
would  be  to  have  a  complete  science. of  such  system. 

A  strictly  deductive  science  of  the  molecular  motion,  and  con- 
sequent function  of  the  elements  of  the  nervous  mechanism,  is,  in- 
deed, a  conceivable  attainment.  But  it  need  scarcely  be  said  that 
we  are  indefinitely  far  from,  not  only  the  attainment,  but  even  the 
reasonable  px'ospect  of  such  a  complete  physical  science  of  the  ner- 
vous system.  None  of  the  questions  raised  respecting  the  struct- 
ure and  functions  of  its  elements,  whether  considered  apart  or  in 
combination,  can  be  answered  with  complete  satisfaction.  More- 
over, the  scientific  study  and  description  of  the  neiwous  mechanism 
is  compelled  from  the  first  to  pui'sue  a  somewhat  different  path 
from  that  open  to  many  forms  of  physical  science.  The  direct 
path  to  the  complete  science  of  the  subject  is  impassable  ;  it  is  ren- 
dered impassable  by  the  most  fundamental  and  universal  of  our 
experiences  respecting  the  nature  of  the  phenomena  of  the  nervous 
system.  The  immediate  effects  of  the  molecular  changes  which 
take  place  in  the  nervous  elements,  even  when  isolated  as  much  as 
possiV^le,  can  only  with  difficulty  be  made  the  subject  of  direct  obser- 
vation.  Histology  has  enormous  difficulties  to  overcome  in  its  effort 


STUDY   OF   NEEVOUS   ELEMENTS.  21 

to  describe  how  these  elements  are  combined  in  the  living  human 
body,  and  physiology  has  like  difficulties  in  the  way  of  its  effort  to 
determine  the  functions  of  those  organs  which  are  constructed  by 
means  of  such  combination.  Only  the  beginning  of  a  theory  which 
shall  correlate  that  mode  of  molecular  motion  which  is  peculiar  to 
nervous  matter  with  other  modes  of  the  motion  of  matter  has  yet 
been  made. 

In  spite  of  the  foregoing  concessions,  a  careful  study  of  the  ele- 
ments of  the  nervous  system  is  the  indispensable  mode  of  approach 
to  the  subject  of  physiological  psychology.  It  is  these  elements 
which,  when  variously  combined,  constitute  all  the  organs  of  the 
system  ;  it  is  they  which,  when  acting  in  combination,  do  all  the 
woi'k  of  the  system. 

§  4.  The  Elements  of  the  Nervous  System  of  Man,  as  elements,  do 
not  differ  in  any  essential  known  respect  from  those  of  other  verte- 
brate animals.  Upon  this  subject,  then,  histology  with  its  micro- 
scope, and  physiology  with  its  experimentation,  can  describe  the 
nerve-fibres  and  nerve-cells  of  other  animals,  and  then  safely  draw 
certain  inferences  from  them  which  will  apply  to  the  case  of  man. 
It  is,  however,  the  development  of  enlarged  or  of  new  organs  by 
the  combination  of  these  elements,  and  the  development  and  elab- 
oration of  function  as  dependent  upon  such  organs,  which  consti- 
tute the  difference  between  the  nervous  system  of  man  and  that  of 
the  lower  animals.  It  is  here  that  histology  meets  with  its  supreme 
difficulties  and  its  most  interesting  problems ;  it  is  here  that  physi- 
ology is  most  insecure  when  trying  to  carry  over  to  the  structure  and 
functions  of  the  human  nervous  mechanism  the  conclusions  which 
have  been  reached  by  experiments  upon  the  lower  animals.  On 
the  contrary,  the  nerve-fibres  and  nerve-cells  of  these  animals  are, 
in  most  respects,  perfectly  competent  to  tell  us  all  we  need  to  know 
regarding  the  nerve-fibres  and  nerve-cells  of  man.  In  describing 
the  constitution,  structure,  and  function  of  the  nervous  elements, 
therefore,  it  will  not  generally  be  necessary  to  pay  attention  to  the 
specific  animal  form  from  which  the  description  is  taken.  In  other 
wordSj  the  discussion  of  the  nervous  elements  belongs  to  the  most 
general  histology  and  physiology  of  the  nervous  system. 

§  5.  The  elements  of  the  nervous  mechanism  require  to  be  con- 
sidered in  three  ways  :  (1)  as  respects  their  chemical  constitution  ; 
(2)  as  respects  their  formal  structure  ;  (3)  as  resjDects  their  general 
physiological  function. 

§  6.  The  Chemistry  of  the  Nervous  System  is  of  necessity  in  an 
exceedingly  unsatisfactory  condition.  The  facts  concerning  which 
perfect  certainty  is  attainable  are  very  few  in  number  ;  the  bearing 


22  CHEMISTEY   OP  NERVOUS   ELEMENTS. 

of  those  facts  on  our  theory  of  nerve-function  is  both  slight  and 
disputable.  Physiological  chemistry  is  in  general  encompassed 
with  many  difficulties.  These  difficulties  are  not  due  simply  to  the 
complex  constitution  of  most  of  the  substances  with  which  it  has 
to  deal.  They  are  also  very  largely  due  to  the  fact  that  these  sub- 
stances are  products  of  life  ;  and  living  tissue  cannot  be  at  the 
same  time  kept  in  normal  condition  and  subjected  to  the  handling- 
necessary  for  chemical  analysis.  As  soon  as  it  is  no  longer  alive, 
or  at  any  rate  long  before  any  chemical  analysis  can  be  completed, 
the  constitution  of  such  tissue  is  changed.  However  carefully  the 
chemical  elements,  the  constituents,  which  enter  into  the  ner- 
vous substance  may  be  preserved,  their  constitution,  their  chemical 
arrangement  and  behavior,  cannot  be  preserved.  It  is  impossible 
— for  example — for  the  chemist  even  to  determine  the  specific 
gravity  of  uncoagulated  blood,  "  except  by  operating  with  extreme 
expedition  and  at  temperatures  below  0°  C." 

Moreovei',  the  difficulties  which  belong  to  the  chemistry  of  all 
living  tissue  are  especially  great  in  the  case  of  the  nervous  tissues. 
In  their  natui'al  state  the  proximate  principles  which  compose  these 
tissues  are  very  complex  and  unstable  compounds.  To  obtain  spe- 
cific portions  or  kinds  of  nervous  substance  free  from  foreign  ingre- 
dients— as,  for  example,  the  axis-cylinder  of  the  nerves,  or  the  rods 
and  cones  of  the  retina — is  by  no  means  always  easy.  The  analysis 
of  such  substance,  when  once  the  substance  is  obtained,  is  often  ex- 
tremely tedious  in  respect  to  process,  and  doubtful  in  respect  to 
result.  Nevertheless,  the  principal  conclusions,  which  may  be  ac- 
cepted with  considerable  confidence  in  their  correctness,  are  as 
follows  : 

§  7.  Nervous  Matter  is  of  two  kinds,. called  white  or  fibrous,  and 
gray  or  vesicular,  which  differ  not  only  in  color  and  microscopic 
structure,  but  also  in  specific  gravity  and  chemical  constitution. 
The  specific  gravity  of  the  white  nervous  matter  is  greater  than  that 
of  the  gray.  Danilewski '  found  the  specific  gravity  of  the  gray 
matter  in  man  to  vary  from  1.02927  to  1.03854  ;  that  of  the  white 
matter  from  1.03902  to  1.04334.  Others  (as  Bastian,  W.  Krause, 
and  L.  Fischer)  calculate  the  mean  specific  gravity  of  the  gray  mat- 
ter at  about  1.031,  of  the  white  at  1.036-1.040.  This  difference  in 
the  weight  of  the  two  is  chiefly  due  to  the  difference  in  the  relative 
amount  of  water  and  of  solids  which  they  contain.  Of  100  parts  of 
each,  from  the  brain  of  the  ox,  the  gray  matter  was  found  to  be 

'  See  Med.  Centralbl  ,  xviii.,  p.  241,  as  cited  by  Dreclisel,  with  apparent 
confidence,  in  Hermann's  Handbuch  der  Physioiogie,  V.,  i. ,  p.  577.  Leipzig, 
1«83. 


NON-PHOSPHORIZED   BODIES   IN   BRAIN. 


23 


composed  of  81.60  parts  of  water  and  18.40  of  solids ;  the  white, 
of  68.35  of  water  and  81.65  of  solids.  The  amount  of  water  is  also 
larger  in  the  brain  of  the  young  animal  than  in  that  of  the  adult. 
The  brain  of  the  foetus  was  found  by  Weisbach  to  consist  of  from 
87.9  to  92.6  parts  of  water.  The  amount  of  water  entering  into  the 
composition  of  the  different  parts  of  the  central  nervous  system  is 
unequal.  The  following  is  a  tabulated  statement  *  of  the  facts  to 
which  allusion  has  just  been  made  : 

Pkopoktion  of  Water  in  One  Hundred  Parts. 


Age,  20  to  30. 

Age,  30  to  50. 

Age,  70  to  94. 

White  substance  of  the  brain 

69.56 
83.36 

78.83 
73.46 
74.43 

68.31 
83.60 

77.87 
73.55 
73.25 

73.61 

Gray  substance  of  the  brain 

Cerebellum     

84.78 
80.34 

Pons  Varolii 

72.74 

Medulla  oblongata    

73.63 

The  amount  of  water  varies  in  the  different  regions  of  the  spinal 
cord.  Bernhardt  found  a  smaller  proportion  of  water  in  the  cervi- 
cal (73.05  per  cent.)  than  in  the  lumbar  (76.04)  region  of  the  cord. 
The  gray  matter  also  contains  more  of  albumen,  lecithin,  and  lactic 
acid  than  the  white,  and  less  of  cholesterin,  fat,  and  protagon. 

§  8.  Of  the  solids  contained  in  the  matter  of  the  nerve-centres, 
more  than  one-half  in  the  gray,  and  about  one-quarter  in  the  white, 
consist  of  certain  proteid  or  albuminous  substances.  Bodies  of 
this  general  class  are  the  only  ones  never  absent  from  the  active 
living  cells  ;  they  therefore  exist  in  the  primordial  structures  of 
all  vegetable  and  animal  organisms,  and  occupy  a  peculiar  place 
among  organic  proximate  principles.  Of  these  proteid  substances 
found  in  the  nerve-centres  very  little  is  as  yet  known.  Gamgee ' 
mentions  three  such  substances — one  soluble  in  water  and  probably 
derived  from  the  gray  matter,  another  a  globulin-like  body  which 
is  dissolved  by  a  ten  per  cent,  solution  of  common  salt,  still  another 
a  myosin-like  body  which  remains  in  solution  when  a  ten  per  cent, 
salt  solution  of  brain  is  boiled. 

§  9.  Three  other  non-phosphorized  bodies  of  different  classes 
from  that  above  mentioned  are  found  in  nervous  tissues  :  these  are 
Cholesterin,  Neurokeratin,  and,  more  doubtfully,  Cerebrin.     Cho- 

'  Derived  from  Weisbach's  observations,  and  found  in  Gamgee,  Physiologi- 
cal Chemistry  of  the  Animal  Body,  i. ,  p.  445.     London,  1880. 

"^  Physiological  Chemistry,  i.,  p.  433  ;  see,  also,  the  article  of  D.  Petrowsky, 
*'  Ziisammensetzung  der  grauen  und  der  weissen  Substanz  des  Gehirns,"  Pflii- 
ger"  s  Archiv,  vii.,  p.  367. 


24  CHEMISTEY   OF   NERVOUS   ELEMENTS. 

lesterin  is  among  the  most  abundant  of  the  constituents  of  the  ner- 
vous tissues — especially  of  tbe  white  matter  of  the  cerebro-spinal 
axis  and  of  the  nerves.  It  is  a  "  monad  alcohol,"  the  only  alcohol 
which  occurs  in  the  human  body  in  a  free  state.  On  account  of  its 
solubility  in  ether,  cold  or  hot,  and  in  warm  alcohol,  cholesterin 
finds  its  way  into  both  ethereal  and  alcoholic  extracts  of  the  ner- 
vous tissues.  It  is  a  non-nitrogenous  body,  crystallizing  in  beau- 
tiful white  crystals,  which,  when  separated  pure  from  its  solutions 
in  ether  or  chloroform,  takes  the  shape  of  fine  needles,  and  when 
sejDarated  from  alcohol  takes  the  shape  of  rhombic  tables.  It  is  sup- 
posed to  exist  preformed  in  the  brain.    Its  formula  is  C^gH^^O  +  H^O- 

Neurokeratin  is  most  easily  derived  by  treating  the  meduUated 
nerve-fibres  with  boiling  alcohol  and  ether,  so  as  to  extract  the  fatty 
matters  of  the  medullary  sheath  ;  in  the  place  of  this  sheath  there 
is  left,  as  a  kind  of  irregular  framework,  a  highly  refractile  sub- 
stance which  resembles  the  horny  matter  of  epidermis  in  its  power 
of  resistance  to  chemical  agents.  This  substance  is  also  found  in 
the  gray  matter  of  the  nerve-centres,  and  in  the  retinal  epithelial 
cells  and  pigment  cells  of  the  choroid  ;  but  not  in  the  non-medul- 
lated  nerve-fibres.  It  contains  nitrogen,  2.93  per  cent,  of  sulphur, 
and  leaves  1.6  per  cent,  of  ash. 

Cerebrin  was  announced  by  Milller,  in  1858,  as  a  non-phosphorized 
nitrogenous  body,  obtained  from  a  precipitate  from  the  brain  when 
pounded  up  with  baryta  water  to  the  consistence  of  thin  milk  and 
then  boiled.  He  described  it  as  a  loose,  Avhite,  very  light  powder, 
destitute  of  smell  and  taste,  soluble  in  boiling  alcohol  and  ether,  but 
insoluble  in  water.  He  gave  to  it  the  formula  Cj^H.^^NO^.  Thudi- 
chum  believes  that  brain  matter  contains  a  class  of  nitrogenous  bod- 
ies free  from  phosphorus,  to  which  he  gives  the  name  of  "cerebrins." 
Gamgee,  however,  thinks  it  very  unlikely  that  a  body  produced, 
like  Mailer's  cerebrin,  "by  the  prolonged  action  of  a  solution  of 
boiling  barium  hydrate  on  so  complex  an  organic  mixture  as  brain 
should  be  a  definite  proximate  principle  of  the  unaltered  organ  ; "  ' 
but  the  same  authority  admits  "  that  the  precipitate  which  sepa- 
rates itself  from  an  alcoholic  solution  of  brain  contains,  besides 
cholesterin,  pi-otagon,  and  the  so-called  lecithins,  "  a  body  for 
which  we  may  retain  the  name  of  cerebrin." 

Nuclein  was  discovered  by  Miescher  in  the  nuclei  of  pus-corpus- 
cles and  in  the  yellow  corpuscles  of  yolk  of  egg.  Other  observers 
subsequently  obtained  it  from  various  other  substances,  especially 
from  the  nuclei  of  the  red  blood-corpuscles  of  birds  and  amphibia. 

'  Physiological  Chemistry,  i. ,  p.  439. 
'Ibid.,  i.,p.  433. 


,  PHOSPHORIZED   BODIES    IIST   BRAIlSr.  25 

Von  Jaksch  '  thinks  lie  has  discovered  nucleiu  in  the  human  brain. 
His  claim  seems  to  be  credited  by  Drechsel.^  Its  formula  is  given 
as  C2gH^;,N^P30j2-  But  the  veiy  existence  of  nuclein,  as  a  definite 
body,  has  been  denied  by  chemists  Hke  Worm-Miiller  and  Gam- 
gee  ;  and  the  analyses  of  Von  Jaksch  do  not  agree  with  those  ob- 
tained from  other  sources  than  the  substance  of  the  human  brain. 
The  whole  question  of  nuclein  must  then  be  left  in  doubt. 

§  10.  No  other  substances  found  in  the  nervous  system  are,  how- 
ever, both  so  interesting  and  so  difficult  to  consider,  from  the  mixed 
chemical  and  psycho-physical  point  of  view,  as  certain  complex  phos- 
phorized  fats.  The  entire  progress  of  our  inquiry  will  make  it  obvi- 
ous how  inadequate  and  misleading  is  the  use  often  made  of  such 
off-hand  remarks  as  the  celebrated  dictum :  "  No  thought  without 
phosphorus."  Yet  it  is  doubtless  true  that  the  highly  elaborate  and 
unstable  compounds  containing  phosphorus,  which  enter  into  the 
composition  of  nervous  matter,  have  a  significance  for  physiological 
and  psychological  researches  such  as  belongs  to  no  other  material 
bodies.  These  comj)lex  bodies  are  especially  characteristic  of  the 
centres  of  the  nervous  system.  The  strife  of  discovery  and  of  con- 
firmatory experiment  has  been  chiefly  carried  on  over  the  following 
three  :  Protagon,  Lecithin,  and  Cerebrin.  Of  these  three,  however, 
probably  only  the  two  former  are  phosphorized  bodies.  The  main 
question  involved  in  controversy  concerns  the  relation  in  which  leci- 
thin and  cerebrin  stand  to  protagon.  Is  protagon  a  definite  prox- 
imate principle  of  the  brain,  and  are  lecithin  and  cerebrin  bodies  of 
ill-defined  properties  and  doubtful  claim  to  existence  as  proximate 
principles  of  the  brain  ?  or,  are  lecithin  and  cerebrin  definite  prox- 
imate principles,  and  is  protagon  a  mechanical  admixture  of  the 
two  ?  The  latter  view  of  protagon  has  been  held  by  Diaconow, 
Hoppe-Seyler,  and  Thudichum  ;  on  the  contrary,  its  claims  to  the 
position  of  the  "  only  well-chax'acterized  phosphorized  proximate 
principle  "  of  the  brain  as  yet  discovered  have  been  defended  (and, 
it  may  be  said,  apparently  established)  by  the  researches  of  Gam- 
gee  and  others. 

Protagon  was  discovered,  as  a  new  proximate  principle  that  -can 
be  separated  from  the  brain,  in  1864,  by  Dr.  Oscar  Liebreich  ;  his 
discovery  was  announced  in  a  paper  ^  published  in  1865.  This  in- 
vestigator gave  to  this  substance  the  name  which  it  still  bears,  as 

'  See  article  "  Ueber  das  Vorkommen  von  Nuclein  im  Menscliengeliirn," 
Pfliiger's  Archiv,  xiii.,  p.  469. 

''^  In  Hermann's  Handb.  d.  Physiol.,  V.,  1.,  p.  578. 

'  'Ueber  die  cbemisclie  Bescbaflfenheit  der  Geliirnsubstanz."  Annalen  der 
Chemie  und  Pbarmacie,  cxxxiv. ,  pp.  29-44. 


26  CHEMISTRY   OF   NERVOUS   ELEMENTS. 

in  his  opinion  the  first  to  be  definitely  ascertained  among  the  spe- 
cific constituents  of  the  brain  (Trpwrayo?,  leading  the  van).  He  as- 
signed to  it  the  formula  Cj^^H^^jN^O^^P.  In  spite  of  subsequent 
denials  and  disproofs  of  its  existence,  the  extremely  careful  and 
often-repeated  researches  of  Gamgee '  and  Blankenhorn  have  cor- 
roborated the  discovery  of  Liebreich.  The  process  by  which  pro- 
tagon  is  obtained  from  the  brain  may  be  thus  briefly  described  (the 
description  will  serve  to  illustrate  in  general  the  processes  of  physi- 
ological chemistry)  :  Perfectly  fresh  ox's  brains  are  freed  from  the 
blood  and  membranes,  and  are  then  digested  for  about  a  day  in 
eighty-five  per  cent,  alcohol ;  from  this  fluid,  when  filtered,  a  quan- 
tity of  white  flocculent  precipitate  is  obtained,  and  the  cholesterin 
and  other  bodies  soluble  in  ether  are  dissolved  out ;  from  the  sub- 
stance left  undissolved,  when  dried  and  reduced  to  powder  and 
digested  for  many  hours  with  alcohol,  and  then  filtered  and  cooled, 
microscopic  crj- stals  separate  themselves,  arranged  for  the  most  part 
in  rosettes.  The  substance  thus  crystallized  is  protagon.  It  is  con- 
sidered by  some  chemists  the  easiest  to  obtain,  and  indeed  the  only 
very  well-established  phosphorized  proximate  principle  of  the  brain. 
Such  a  material  substance  is  indeed  a  long  way  removed  from  the 
living  nervous  mass,  with  its  capacity  for  exercising  such  marvel- 
lous physiological  and  psycho-j)hysical  functions.  But  it  is  the  best 
representative  that  chemistry  can  as  yet  present  of  a  scientific  result 
upon  which  to  base  any  attempt  to  point  out  definite  relations  be- 
tween psychical  activities  and  the  chemical  constitution  of  those 
complex  phosphorized  fats  which  exist  in  the  central  nervous 
mechanism.  The  empirical  formula  of  protagon,  as  given  by  Gam- 
gee,  is  C|j„H3„„Nj.P03j.  It  has  been  made  highly  probable  that  pro- 
tagon cannot  be  a  compound  or  mixture  of  cerebrin  and  lecithin  ;  it 
may,  then,  be  announced  as  a  proximate  principle  of  the  brain. 

Lecithin  is  an  organic  phosphorized  compound  which  exists  in 
large  quantities  in  ova,  spermatozoa,  etc.,  as  well  as  in  the  nervous 
tissues.  It  is  described  as  a  yellowish-white,  waxy,  very  hygro- 
scopic solid,  which  in  thin  layers  shines  with  a  silky  lustre.  It  is 
soluble  in  ether  and  alcohol ;  on  being  stirred  with  water  it  forms  a 
starch-like  solution  difficult  to  filter.  Diaconow  assigns  to  it  the  for- 
mula C.^H^^NPOj,  -f  H^O.  Gamgee  supposes  that  the  lecithin  of  Dia- 
conow is  only  one  of  a  group  of  similar  bodies  which  possess  a  higher 
percentage  of  phosphorus  than  protagon,  and  the  "general  smeary 
characters  "  of  lecithin.  We  may,  then,  speak  of  "  the  lecithins  "  as 
highly  phosphorized  compounds  existing  in  the  matter  of  the  brain. 

'  See  his  Physiological  Chemistry,  i. ,  pp.  425-429  ;  and  article  in  the  Jour 
nal  of  Physiology,  ii.,  pp.  113-131. 


nsro:EGA]sric  bodies  iisr  beaiis'. 


27 


The  various  products  of  the  decomposition  of  protagon  and  leci- 
thin it  is  not  necessary  to  describe.  Neurin  is  the  only  one  of 
these  products  which  deserves  for  our  purpose  even  to  be  named. 
It  may  be  obtained  from  either  protagon  or  lecithin.  Dr.  Thudi- 
chum's  elaborate  "  Eesearches  on  the  Chemical  Constitution  of  the 
Brain  "  ^  conclude  that  at  least  three  well-defined  groups  of  phos- 
phorized  bodies  may  be  separated  from  the  brain  ;  these  are  dis- 
tinguished as  (1)  kephalins,  (2)  myelins,  (3)  lecithins.  The  exist- 
ence of  a  group  of  bodies  which  may  be  termed  "lecithins "  has  just 
above  been  declared  probable.  Thudichum  thinks  that  all  these 
bodies  contain  phosphoric  acid  combined  proximately  with  glyce- 
rin, but  "  differ  in  the  manner  in  which  they  contain  the  nitrogen 
and  the  acid  radicles  which  constitute  the  great  bulk  of  their  sub-' 
stance."     The  researches  of  Dr.  Thudichum  still  await  confirmation. 

§  11.  In  addition  to  the  substances  already  mentioned,  the  brain 
contains  certain  extractive  matters  which  are  found  also  in  other 
tissues,  especially  in  muscle.  Among  these  bodies  are  creatin, 
inosite,  xanthin,  and  lactic  acids. 

§  12.  The  brain  also  contains  an  extremely  small  amount  of  inor- 
ganic matters— so  small,  indeed,  that  few  facts  can  be  relied  on 
concerning  it.  The  estimates  of  this  amount  vary  from  0.1  to  1 
per  cent,  of  the  fresh  brain.  Among  such  inorganic  matters  are 
alkaline  phosphates  and  sulphates,  chalk,  magnesia,  oxide  of  iron, 
etc.  It  is  said  that  the  ash  of  the  gray  matter  has  an  alkaline  reac- 
tion, that  of  the  white  matter  an  acid  reaction,^  and  that  the  reac- 
tion of  the  former  during  life  is  acid,  while  that  of  the  latter  is 
neutral  or  weak  alkaline. 

§  13.  All  quantitative  analyses  of  the  brain  are  exceedingly  doubt- 
ful ;  the  older  results  are  wholly  worthless.  The  following  table  of 
Petrowsky,'  which  gives  the  chief  organic  constituents  of  the  brain 
of  the  ox,  is  an  object  of  interest  rather  than  of  complete  confidence  : 


Substance. 

Gray  Matter. 

White  Matter, 

Albumen  and  gelatin 

55.87+ 
0,53+ 

17.24+ 

18.68  + 

6.71  + 

1.45  + 

per  cent. 

24.72  + 
9.55- 
9.90+ 

51.91- 
3.34+ 
0.57+ 

per  cent. 

Cerebrin 

Lecithin 

Cholesterin  and  fats  

Substances  insoluble  in 
Salts 

ether 

'  Reports  of  Medical  Officer  of  the  Privy  Council  and  Local  Government 
Board,  1874,  pp.  113  ff. 

2  See  Gamgee,  Physiological  Chemistry,!.,  p.  445;  Hermann,  Handb.  d. 
Physiol.,  v.,  i.,  p.  577. 

^  "  Zusammensetzung  der  grauen  und  der  weissen  Substanz  des  Gehirns," 
Pfliiger's  Archiv,  vii.,  p.  367. 


28  CHEMISTEY   OF   NERVOUS   ELEMENTS. 

§  14.  The  specific  chemistry  of  the  elements  of  the  nervous  sys. 
tem,  or  of  the  various  parts  of  such  elements  which  histological 
science  reveals,  is  yet  more  meagre  and  doubtful  than  its  general 
chemistry.  The  micro-chemistry  of  the  nerve-cells  tells  us  simply 
that  they  are  in  the  main  protoplasmic,  and  therefore  rich  in  pro- 
teid  substances  ;  and  since  an  analysis  of  the  two  kinds  of  nervous 
matter  shows  that  the  gray  is  much  the  poorer  in  complex  phos- 
phorized  constituents  and  in  cholesterin,  we  conclude  that  the  cells 
which  enter  so  largely  into  the  gray  matter  are  also  poor  in  the 
same  substances.  The  different  structural  parts  of  the  nerve-fibres 
have  doubtless  a  different  chemical  constitution.  This  is  proved 
by  the  difference  in  their  appearance  under  the  microscope,  by  the 
different  action  of  reagents  upon  them,  and,  to  some  extent,  by 
chemical  analysis.  The  neurilemma,  or  membranous  envelope  of 
the  nerve-fibres,  like  the  sarcolemma,  on  prolonged  boiling,  yields 
gelatin.  The  axis-cylinder  appears  to  be  a  mixture  of  proteid  with 
complex  fat-like  bodies.  The  white  substance  of  Schwann  is  rich 
in  complex  phosphorized  fats,  in  cholesterin,  and  in  the  so-called 
cerebrins. 

The  researches  of  Kiihne  '  and  others — for  the  most  part  his 
pupils — have  developed  certain  interesting  results  with  respect  to 
the  chemical  constitution  and  chemicals  change  of  the  nervous  tis- 
sue of  the  eye.  Many  of  the  various  non-nervous  parts  of  the  ear 
and  the  eye  have  been  carefully  analyzed.  The  extremely  small 
amount  of  such  material  which  is  obtainable  for  chemical  analysis 
is  one  reason  why  so  little  can  be  known  concerning  the  chemical 
constitution  of  the  substance  of  the  retina.  It  is  said  to  have  an 
acid  reaction.  It  is  a  fair  surmise,  on  general  grounds,  that  it  con- 
tains the  same  bodies  as  the  central  nervous  system.  The  two  seg- 
ments into  which  the  rods  and  cones  break  up  exhibit  marked  dif- 
ferences in  their  chemical  as  well  as  optical  characters.  The  inner 
segments  are  composed  of  protoplasm  of  "a  marvellous  transpar- 
ency." The  outer  limbs  of  the  rods  have  an  external  envelope 
which  agrees  in  its  physical  characters  with  neurokeratin.  This 
envelope  encloses  a  mixture  of  proteid  bodies  and  of  other  sub- 
stances similar  to  those  found  in  the  other  nervous  tissues. 

§  15.  If  knowledge  of  the  chemical  constitution  of  the  nervous 
system  is  so  far  behind  what  Ave  could  wish,  knowledge  of  the 
chemical  proce  ses  and  chemical  changes  which  are  connected  with 
the  physiological  functions  of  this  system  must  be  declared  to  be 

'  For  a  list  of  papers  by  Kuhne  and  liis  pupils  on  this  subject,  see  Gamgee, 
Physiological  Chemistry,  i.,  p.  462  f. ;  and  for  an  account  by  him  of  his  re- 
searches and  their  results,  see  Hermann,  Handb.  d.  Physiol.,  I.,  i.,  pp.  235  ff. 


USTTRA-MOLECULAK   OXYGEN.  29 

almost  wholly  wanting.  Even  the  beginnings  of  scientific  general 
statements,  ox'  laws,  respecting  the  relations  between  the  chemical 
constitution  of  the  nervous  system  and  its  various  physiological 
activities  have  yet  to  be  made.  Different  investigators  will  doubt- 
less differ  as  to  the  prospect  for  such  discovery  in  the  future. 
When  chemistry  can  deduce  the  molecular  behavior  of  the  most 
highly  complex  chemical  compound  from  the  nature  and  number 
of  its  component  chemical  elements,  and  physiology  can  definitely 
connect  all  the  physiological  functions  of  nervous  matter  with  the 
molecular  motions  of  its  chemical  constituents,  we  shall  have  the 
means  for  a  strictly  scientific  solution  of  such  problems. 

§  16.  It  need  scarcely  be  said  that  we  have  little  knowledge  re- 
specting the  relation  which  exists  between  the  chemical  constitu- 
tion and  chemical  processes  of  the  nervous  system,  on  the  one  hand, 
and,  on  the  other,  the  jDhenomena  of  so-called  mind. 

Nevertheless,  certain  important  general  relations  may  be  point- 
ed out  between  the  chemical  nature  of  the  nervous  mechanism 
and  its  psycho-physical  functions.  The  extremely  high  organiza- 
tion and  chemically  sensitive  constitution  of  this  mechanism  are 
bej'ond  doubt  related  to  all  its  distinctive  functions.  Like  every 
other  natural  material  structure,  the  nervous  system  is  obviously 
adapted  to  its  peculiar  kind  of  work.  Chemically  considered,  it 
appears  as  composed  of  a  number  of  extremely  complex  and  highly 
unstable  compounds.  It  therefore  holds  in  its  chemical  consti- 
tution a  large  amount  of  disposable  energy  ;  this  energy  it  yields 
readily  when  the  equilibrium  of  its  molecules  is  in  any  way  dis- 
turbed. Within  certain  limits,  it  explodes  with  increasing  surren- 
der of  its  disposable  energy  as  the  number  and  intensity  of  the 
demands  upon  it  are  increased — very  much  as  would  a  gun  which 
should  be  arranged  so  as  to  go  off  with  greater  energy  as  the  press- 
ure of  the  finger  on  its  trigger  is  repeated  or  increased. 

It  is  probable  that  the  substance  of  the  nerves  is  the  seat  of  a 
chemical  synthesis,  as  the  result  of  which  still  more  complex  bodies 
are  constructed  from  the  already  complex  alimentary  material  fur- 
nished by  the  blood ;  such  bodies  have  a  high  value  as  combus- 
tibles, and  thus,  as  has  been  said,  possess  a  significant  amount  of 
disposable  energy.  The  relation  of  a  supply  of  oxygen  to  the 
nerve-centres  is  also  important  to  notice.  The  nexwe-fibres  require 
comparatively  a  small  amount  of  oxygen.  It  may  be  conjectux*ed 
that  in  their  case,  as  in  the  case  of  muscle-fibre,  intra-molecular 
oxygen  is  of  some  use  in  preparing  explosive  materials.  But  at 
present  we  must  be  satisfied  Avith  conjecture  on  this  point.  On  the 
contrary,  the  vascular  xiature  of  the  central  organs  creates  a  pre- 


80         FORM  OF  THE  NERVOUS  ELEMENTS. 

sumption  that  the  chemical  processes  which  have  their  seat  in  them 
require  an  abundance  of  oxygen.  Experience  confirms  this  pre- 
sumption. The  respiratory  centre  in  the  medulla  oblongata  is 
chiefly  controlled  in  its  action  by  the  amount  of  oxygen  which 
reaches  it  in  the  blood.  The  phenomena  of  consciousness  vanish 
when  the  supply  of  oxygenated  blood  is  cut  off  from  the  brain. 

Although  we  are  still  in  the  dark  as  to  the  precise  significance  of 
the  visual  purple,  the  phenomena  which  the  study  of  it  has  brought 
to  light  are  suggestive  of  unseen  chemical  processes  that  are  set  up 
in  the  retina,  and  so  serve  as  stimulus  for  the  fibrils  of  the  optic 
nerve.  In  general  we  know  that  certain  sensations  are  dependent 
upon  the  chemical  constitution  and  activity  of  the  various  end- 
organs  of  sense. 

Further  researches  will  undoubtedly  greatly  enlarge  our  knowl- 
edge of  those  facts  of  relation  which  exist  between  the  chemical 
constitution  and  changes  of  the  nervous  mechanism  and  the  phe- 
nomena of  psychical  life.  Perhaps  such  particular  .statements  of 
fact  may  be  gathered  into  such  more  general  statements  of  fact, 
verifiable  by  experiment,  as  we  consider  sufficient  to  constitute 
scientifically  established  laws.  But  lohy  certain  chemical  constitu- 
ents, when  combined  and  changed  in  definite  fashion,  should  be 
specifically  connected  with  certain  conscious  experiences  will  always 
remain  an  unanswerable  inquiry. 

§  17.  From  the  chemical  constitution  of  the  elements  of  the  ner- 
vous system  we  now  pass  to  their  Structural  Form.  The  science 
which  must  be  our  guide  is  no  longer  chemistry,  but  microscopic 
anatomy,  or  histology;  this  science  furnishes  us  with  a  large  amount 
of  trustworthy  information  mingled  with  a  still  larger  amount  of 
conjecture  and  doubt.  Even  the  number  of  those  elements  upon 
which  histology  is  entitled  to  focus  its  microscope  and  declare  that 
such,  and  no  others,  are  capable  of  performing  distinctively  ner- 
vous functions  can  scarcely  be  said,  as  yet,  to  be  placed  beyond  all 
doubt ;  neither  can  it  be  claimed  that  the  microscope  has  yet  dem- 
onstrated the  ultimate  structure  of  those  two  species  of  such  ele- 
ments the  reality  of  whose  nervous  functions  is  beyond  doubt. 

It  is  customary  to  speak  of  nerve-fibres  and  ganglion-cells  as  the 
only  structural  elements  of  the  nervous  system.  If,  however,  by  the 
term  "  ganglion-ceU  "  we  intend  only  such  bodies  as  histology  usu- 
ally describes  under  this  type  (for  example,  the  so-called  motor 
ganglion-ceiis  of  the  spinal  cord)  the  limitation  is  without  sufficient 
warrant.  For  there  are  many  cells,  which  almost  certainly  have 
some  significance  as  parts  of  the  nervous  system,  that  differ  in 
form  very  widely  from  the  typical  ganglion-cell.     Moreover,  by  such 


COEPUSCLES   OF  DOUBTFUL   CHARACTER.  31 

an  off-hand  twofold  division  the  important  question  is  often  silently 
passed  by :  What  is  the  significance  for  the  nervous  functions  of  that 
diffuse,  finely  granular  substance,  found  in  considerable  quantity  in 
the  great  nerve-centres,  and  called  neuroglia,  or  nerve-cement  {Ner- 
ven-kitt ;  Kittsubstanz)  ?  This  substance  is  most  frequently  classed 
with  the  connective  tissue;  but,  according  to  Henle,*  "it  is  at  all 
events  to  be  distinguished  from  connective  tissue  on  account  of  its 
chemical  properties."  That  certain  microscopic  forms  of  so-called 
"neuroglia"  are  largely  unlike  other  forms  recognized  as  being 
nerve-cells  beyond  doubt  cannot  be  argued  in  proof  of  its  ina- 
bility to  perform  any  of  the  strictly  nervous  functions,  except  upon 
the  basis  of  the  assumption  that  we  already  know  beyond  reasonable 
question  what  are  all  the  elementary  structural  forms  of  true  ner- 
vous matter.  But,  assays Eckhard,^  "if  we  start  the  inquiry,  what 
formal  elements  of  the  brain  and  spinal  cord  take  part  in  the  activi- 
ties of  these  (the  nervous)  organs,  and  in  what  way  do  they  take 
part,  we  are  able  to  give  to  it  only  a  very  unsatisfactory  answer." 
We  are  not  in  a  position,  then,  either  to  affirm  or  to  deny  abso- 
lutely the  claim  sometimes  set  up  for  the  neuroglia,  that  it  con- 
tains true  nervous  elements. 

It  is  best  to  recur  to  the  facts  which  microscopic  anatomy  dis- 
closes as  a  basis  for  classifying  the  different  structural  elements  of 
the  nervous  system.  These  may  be  briefly  described  as  follows  : ' 
As  to  the  true  nervous  character  of  fibres  of  various  kinds,  not  only 
as  conducting  bands  between  the  nervous  centres  and  the  peripheral 
parts  of  the  body,  but  also  within  the  substance  of  these  centres, 
there  is  no  dispute.  Nerve-fibres  undoubtedly  constitute  one  of 
the  structural  elements  of  the  nervous  mechanism.  Besides  the 
nerve-fibres,  histology  distinguishes  in  the  gray  substance  of  the 
nervous  centres — where  all  the  structural  elements  of  the  nervous 
system  are  to  be  found  in  greatest  abundance  and  variety — three 
other  species  of  structural  form.  Such  are  (a)  certain  cells,  known 
more  particularly  as  the  "  ganglionic  nerve-cells."  These  cells  (to 
be  described  more  minutely  hereafter)  are  irregular  magses  of  finely 
granular  protoplasm,  possessed  of  a  clear  nucleus  and  one  or  more 
nucleoli,  and  sending  off  one  or  more  processes. 

(6)  Corpuscles,  consisting  either  of  naked  nuclei  or  of  nuclei 
with  only  a  small  amount  of  surrounding  protoplasm,  and  having 
various  shapes  sometimes  difficult  to  make  out,  are  also  found 
abundantly  in  the  gray  matter  of  certain  nervous  centres.     Such 

*  Anatomie  des  Mensclien.     Text,  p.  306.     Braunschweig,  1880. 

^  Hermann,  Handb.  d.  Physiol  ,  II.,  ii.,p.  15. 

^  Comp.  Henle,  Anatomie  des  Menschen.     Text,  p.  306. 


32  FOEM    OF   THE   ISTERVOUS    ELEMENTS. 

bodies  are  usually  much  smaller  than  the  cells  of  undoubted  ner- 
vous character  described  above,  many  of  them  being  scarcely  more 
than  ■j-g'iro  - -gVo  0"'  ^^'  ^ven  -g-uVoj  ^^  ^^  inch  in  diameter.  Some  of 
them,  like  the  typical  ganglionic  cell,  give  off  processes  which  are 
thought  to  be  continuous  with  nerve-fibres.  It  is  altogether  prob- 
able that  these  cells  of  the  second  class  differ  only  in  their  dimen- 
sions from  the  cells  of  the  first  class.  In  some  places  (for  example, 
in  the  cortex  of  the  cerebrum,  or  large  brain)  they  appear  to  have 
the  characteristics  of  transitional  forms  between  the  undeveloped 
gi'anules  of  the  same  class  and  the  more  highly  developed  ganglion- 
cells.  In  other  places  (as  in  the  cerebellum)  they  form  indeiDend- 
ent  layers.  They  may  be  described  as  nuclei  "invested  by  only 
a  small  quantity  of  cell-substance."  '  Some  are  multipolar,  some 
bipolar,  some  unipolar.  Admitting,  as  we  seem  compelled  to  do  on 
account  of  their  resemblance  to  the  typical  form  of  the  ganglionic 
nerve-cell,  that  some  of  these  cells  are  true  nervous  elements,  it  is 
impossible  for  histology  to  draw  the  line  through  the  entire  class, 
and  so  to  affirm  beyond  doubt  that  any  of  them  are  without  claim 
to  be  counted  among  such  elements. 

(c)  The  diffuse,  finely  granular  substance,  already  referred  to  as 
so-called  "neuroglia,"  which  fills  in  the  gaps  between  the  nerve- 
fibres  and  the  cells  of  the  two  preceding  classes,  constitutes  the  other 
form  of  matter  observed  in  the  nervous  centres.  It  exists  in  quan- 
tity large  enough  to  form  an  essential  constituent  of  some  locali- 
ties of  the  brain  and  spinal  cord.  It  is  not  always  clear,  however, 
to  what  this  appearance  of  granular  or  molecular  matter,  in  which 
the  nerve-cells  seem  embedded,  is  due.  According  to  some  author- 
ities, it  may  result  from  a  confused  interlacement  of  fine  nerve- 
fibrils  and  fine  ramifications  of  nerve-cells  ;  or  from  the  crushing 
of  such  nervous  matter  in  the  process  of  examination."  The  neu- 
roglia itself  is  described  as  a  delicate  reticulum,  or  network,  in 
which  certain  small  cells  (neuroglia-cells)  supposed  to  belong  to 
the  sustentacular  tissue,  and  other  more  conspicuous  cells,  usually) 
stellate  in  section  ("  cells  of  Deiters  "),  are  found. 

§  18.  Of  the  three  foregoing  kinds  of  structural  forms  found  in 
the  gray  nervous  matter,  it  is  perhaps  safest  to  class  the  first  two 
together  under  the  term  "nerve-cells."  We  should  then  have  to 
remember  how  greatly  these  vary  in  size  and  formation — all  the 
way  from  the  naked,  or  almost  naked,  nucleus  to  the  large  ganglion- 
cell  with  its  many  processes  and  complex  microscopic  structure. 

'  See  Max  Schultze  in  Strieker,  Human  and  Comparative  Histology,  i.,  p 
183.     London,  1870. 

'■'See  Quain's  Elements  of  Anatomy,  ii.,  p   149.     London,  1882. 


STRUCTUEE    OF   A   NERVE. 


33 


The  last  of  the  three  (neuroglia)  may  then  be  regarded  as  a  susten- 
tacular  tissue  ;  though  with  the  confession  that  in  the  brain  and 
spinal  cord  it  is  by  no  means  always  easy  to  distinguish  susten- 
tacular  from  true  nervous  tissue.' 

Of  the  structures  known  as  nerve-fibres  and  nerve-cells,  his- 
tology enables  us  to  give  a  further  more  minute,  if  not  a  com- 
plete, description  ;  it  also  excites  our  interest  by  making  it  possi- 
ble to  conjecture  what  is  the  regular  anatomical  relation  between 
the  two.  When  combined  wdth  physiological  researches,  histology 
also  enables  us  to  make  considerable  progress  toward  distinguish- 
ing the  separate  as  well  as  the  combined  functions  of  these  ele- 
ments. We  consider,  then,  with  particular  detail,  the  structure  and 
functions  of  nerve-fibres  and  ganglionic  nerve-cells. 

§  19.  What  is  ordinarily  called  a  nerve  appears  to  the  naked  eye, 
when  dissected  from  an  animal,  as  a  cord  of  a  whitish  or  grayish 


Fig.  1. — Cross-section  of  the  Sciatic  Nerve  of  Man.  ^/,.  (After  Key  and  Retzius.)  The  left  lower 
half  is  schematic,  n,  n.  Bundles  of  nerve-fibres,  surrounded  by  pn,  pn,  the  perineurium  :  be- 
tween them  appears  the  connective  tissue,  epineuruim  (ep,  ep),  and  adipose  substance  (ad). 

color,  and  of  uniform  stnicture.  The  nerve  is  really,  however,  one 
or  more  bundles,  or  fascicles,  of  a  larger  or  smaller  size,  bound  to- 
gether by  connective  tissue.  Accordingly,  on  following  it  toward 
its  peripheral  termination  we  find  that  it  divides  and  subdivides 
until  its  subdivisions  consist  of  a  sinaie  nervous  element  called  a 


'  Comp.  Ranvier,  Traite  Tecliuique  d'Histologie,  i. ,  p.  717.     Paris,  1875. 
3 


34  FOEM   OF   THE   NERVOUS   ELEMENTS. 

Nerve-fibre.  The  bundles  have  a  special  sheath  formed  of  con- 
nective tissue  {neurilemma,  or  perineurium),  which  in  the  finest 
branches  becomes  reduced  to  a  single  layer  of  cells  cemented  to- 
gether edge  to  edge,  and  is  called  the  "sheath  of  Henle."  On  fol- 
lowing the  fibres  backward  again  toward  the  central  organs,  it  is 
found  that  several  of  them  are  bound  together  to  form  a  nerve- 
fascicle  ;  a  small  amount  of  fibrillar  connective  tissue  appears  be- 
tween the  several  fibres  within  the  same  sheath  ;  the  character  of 
the  sheath  itself  is  changed,  and  it  becomes  attached  to  surround- 
ing structures  by  a  layer  of  connective  tissue.  It  is  the  fibres  into 
which  the  nerves  break  up  on  being  followed  toward  their  periph- 
eral terminations,  or  by  junction  of  which,  successively,  they  are 
composed  on  being  followed  toward  their  central  termination,  that 
are  to  be  considered  as  the  true  elements  of  the  nervous  system. 

§  20.  Such  nerve-fibres  as  compose  the  nerves  which  stretch  from 
the  central  organs  to  the  peripheral  parts  of  vertebrate  animals 
may  readily  be  divided  into  two  classes  :  one  called  meduUated 
fibres  or  nerve-tubes,  and  the  other  non-medullated  fibres  or  fibres 
of-Remak.  Nerves  in  which  there  is  a  large  proportion  of  medul- 
lated  fibres  have  a  characteristic  white  or  watery  appearance  ;  those 
in  which  only  non-medullated  fibres,  or  only  a  few  medullated  fibres, 
exist  are  grayish  and  slightly  translucent.  Vertebrates  alone  have 
the  former.  The  medullated  nerve-tubes  belong  particularly  to 
the  cerebro-spinal  system,  and  are,  therefore,  of  prime  interest  in 
psycho-physical  researches  ;  the  fibres  of  Remak  are  very  abundant 
in  all  the  nerves  belonging  to  the  sympathetic  system.  This  two- 
fold division  of  nerve-fibres,  while  admitting  of  easy  application  to 
the  constituent  elements  of  the  nerve-trunks,  becomes  more  diffi- 
cult when  we  attempt  to  carry  it  out  within  the  complex  nervous 
matter  of  the  central  organs.  Here  Max  Schultze  '  points  out  sev- 
eral varieties  of  nerve-fibres.  There  are,  first,  those  "very  fine 
threads  which  lie  on  the  extreme  verge  of  microscopic  mensura- 
tion," and  which  require  an  enlargement  of  from  500  to  800  diame- 
ters in  order  to  be  made  visible.  In  such  fibres  no  internal  struct- 
ure can  be  detected  by  the  microscope.  To  these  Schultze  gives 
the  name  of  "  primitive  nerve-fibrils."  Second  :  certain  very  deli- 
cate transparent  fibres  of  albuminous  composition,  and  distinguished 
from  the  foregoing  by  their  greater  size  and  their  manifest  fibrillar 
structure,  are  found  in  the  central  organs.  These  are  the  so-called 
naked  axis-cylinders.  Both  the  foregoing,  when  invested  with  a 
medullary  sheath,  become  converted  into  the  third,  or  medullated, 
form  of  nerve-fibre.  These  fibres  in  the  nerves,  while  running  be- 
'  See  Strieker's  Human  and  Comparative  Histology,  i. ,  pp. ,  147  £E. 


VARIETIES   OF   NERVE-FIBEES.  35 

tween  the  central  orgaus  and  the  end-organs,  become  invested  with 
a  delicate  membrane,  and  are  thus  converted  into  nerve-tubes  of 
the  well-known  threefold  structure.  A  fourth  form  of  nerve-fibre 
occurs  in  the  peripheral  nerves,  and  is  distinguished  from  the  fore- 
going by  the  absence  of  the  medullary  sheath.  This  is  the  pe- 
ripheral non-medullated  fibre,  or  fibre  of  Eemak,  already  alluded  to. 
As  they  appear  to  the  mici'oscopist,  then,  on  an  examination  of  all 
the  kinds  of  nerve-fibres  which  are  found  in  all  the  different  parts 
of  the  nervous  system,  the  following  table  of  varieties  is  proposed 
by  Schultze : 

I.  Non-medullated  (J"  P^iiiiitive  fibrils. 

oi  -<  2.  Fascicuh  of  primitive  fibrils. 

I  3.  These  last,  with  a  sheath  of  Schwann. 

r  1.  Primitive  fibrils  with  medullary  sheath. 

II.  MeduUated  fibres.  J  ^-  ^^f^^'^^^  «f  primitive  fibrils  with  such 
j  sheath. 

I  3.  These  last,  with  a  sheath  of  Schwann. 

The  exposition  of  Schultze,  although  of  value  in  setting  forth 
the  variety  of  forms  in  which  the  nerve-fibre  is  actually  found  by 
the  histologist,  does  not  constitute  an  objection  to  the  twofold  di- 
vision first  proj)osed.  On  the  contrary,  it  leads  directly  to  such  a 
division.  For  it  will  be  noticed  that  both  of  the  chief  classes  of 
fibres  are  regarded  as  composed  of  a  number  of  primitive  fibrils  ; 
both  are  also  regarded  as  becoming  invested  in  their  peripheral 
course  with  an  outside  membrane.  The  two  classes,  however,  are 
really  derived  upon  the  basis  of  the  fact  that  some  of  the  primitive 
fibrils,  whether  they  have  already  become  invested  with  this  mem- 
brane or  not,  possess  a  medullary  sheath,  and  others  do  not.  It  is 
the  presence  or  absence  of  this  medullary  sheath  which  constitutes 
the  one  important  difference  between  the  different  classes  of  nerve- 
fibres. 

§  21.  MeduUated  nerve-fibres,  or  nerve-tubes,  have  a  threefold 
structure.  Such  fibres,  when  separated  by  teasing  with  needles 
from  the  fascicle  of  nerve-fibres  and  examined  under  the  microscope 
while  still  fresh,  appear  pellucid,  with  a  central  part  and  a  border 
on  each  side,  like  a  translucent  liquid  in  a  tube  of  translucent 
walls.  The  lines  of  this  double  contour  are  at  first  comparatively 
sharp  and  regular ;  lengthening  the  focus  of  the  instrument  ob- 
scures slightly  the  central  part,  and  causes  the  parts  on  the  border 
to  appear  brighter.  Little  by  little  the  appearance  of  the  fibres 
changes.    The  contours  become  irregular,  and  the  substance  (myelin) 


66 


rOEM  OF  THE  NERVOUS  ELEMENTS, 


composing  the  borders  becomes  folded,  striated,  and  granulated  in 
appearance.  The  myelin  wells  over  the  sides  of  the  ends  of  the 
fibres  in  irregular  globular  or  contorted  masses.  Occasionally  a 
pale  filament  may  be  seen  projecting  beyond  the  torn  end  of  a 
fibre.  Owing  to  the  fact  that  various  solutions  have  different  effects 
upon  the  different  parts  of  the  nerve-fibres,  it  is 
possible  to  prepare  specimens  which  shall  exhibit 
clearly  their  threefold  structure.  Thus,  for  ex- 
ample, a  solution  of  picrocarminate  of  ammonia 
colors  the  central  part  of  the  fibre,  or  axis-cylin- 
der, but  not  the  myelin  ;  whereas  osmic  acid 
stains  the  axis-cylinder  slightly,  the  myelin  thor- 
oughly, but  not  the  substance  of  the  annular 
rings.  By  use,  then,  of  various  reagents,  to  color 
the  nerve-fibres,  and  by  numerous  observations 
of  them  under  various  circumstances,  their  three- 
fold nature  in  a  living  state  is  thought  to  be  dem- 
onstrated. We  distinguish,  then,  in  the  medul- 
lated  fibres  :  (1)  An  outer  membrane,  extremely 
thin,  pellucid,  with  nuclei  in  it,  and  called  the 
primitive  sheath  or  sheath  of  Schioann  ;  (2)  an  in- 
terior layer  of  dimly  granular,  white,  and  highly 
Fig.  2.— Medulla  ted  refracting  substaucc,  semi-liquid  during  life,  and 
i^Tmrtaeguiar contour  after  death  undergoing  a  jorocess  resembling  co- 
sbowing.  (schwaibe.)  agulatiou— Called  the  medullanj  sheath  or  loMte 
substance  of  Schwann;  and  (3)  a  cylindrical  band  of  albuminous 
material,  transparent,  but  with  marks  of  fibrillation — called  the 
axis-cylinder.  Only  the  last  is  supposed  to  constitute  the  essen- 
tial nervous  structure  ;  for,  as  we  have  already  seen,  many  nerve- 
fibres  are  simj^le  naked  axis-cylinders,  and  all  fibres  for  a  certain 
distance  from  the  cells  in  which  they  originate  are  devoid  of  the 
medullary  sheath.  There  is  considerable  evidence  that  the  presence 
of  this  sheath  depends  upon  the  need  of  insulation  only. 

§  22.  Besides  the  threefold  longitudinal  structure  of  the  medul- 
lated  nerve-fibre,  we  have  to  notice  certain  structural  modifications 
that  occur  at  intervals  in  its  length.  The  peripheral  nerve-tube 
does  not  run  along  as  a  regular  cylinder,  but  places  of  constriction 
appear  at  certain  points  situated  beneath  the  outer  sheath  ;  these 
constrictions  are  made  at  the  expense  of  the  medullary  sheath  or 
myelin.  They  are  called  annular  constrictions  or  nodes  of  Eaiivier , 
the  portion  of  nerve-fibre  included  between  two  of  these  constric- 
tions is  called  an  interannular  segment.  At  the  constrictions  the 
ends  of  the  segments  of  the  outer  sheath  are  joined  together  by  a 


MEDULLATED    NEEVE-FIBRES. 
A  B 


37 


ar-fi 


i"T- 


Fig.  3.— a,  Medullated  Nerve-fibres  from  the 
Sciatic  of  a  Rabbit,  stained  with  osmic  acid, 
and  dissociated  in  water.     (Ranvier.) 

B,  Single  Fibre  Enlarged  ^""/j,  a,  a.  An- 
nular constrictions,  or  nodes  of  Ranvier, 
nearly  midway  between  which  is  n,  the  nu- 
cleus, with  protoplasm,  p,  surrounding  it ; 
ca,  axis-cylinder. 


Fig.  4. — Medullated  Nerve-fibres.  (Schwalbe.) 
rt,  Ajds-cylinder  ;  s,  sheath  of  Schwann ;  n, 
nucleus  ;  p,  p.  granular  substance  at  the  poles 
of  the  nucleus  ;  r,  r,  Ranvier's  nodes,  where 
the  medullary  sheath  is  interrupted  and 
the  axis-cylinder  appears ;  i,  »",  incisures  of 
Schmidt. 


38 


FORM  OF  THE  NERVOUS  ELEMENTS. 


tbin  layer  of  cementing  substance  which  extends  inward  toward 
the  axis-cyUnder.  These  interannular  segments  of  the  nerve-fibre 
vary  greatly  in  length.  When  several  nerve-fibres  lie  parallel  with 
each  other,  the  segments  of  four  or  five  of  them  often  seem  to  have 
about  the  same  length,  and  then  the  series  appears  interrupted  by 
some  segment  considerably  longer  or  shorter  than  the  rest. 

Each  interannular  segment  of  a  nerve-fibre  has  a  flattened  ellip- 
tical nucleus,  situated  nearly  equidistant  between  the  two  annular 
constrictions  which  limit  the  segment.  This  nucleus 
often  has  a  nucleolus  ;  between  the  nucleus  and  the 
myelin  there  exists  a  minute  mass  of  protoplasm  which 
is  spread  beneath  the  membrane  of  Schwann  and  fixed 
to  it. 

Scattered  irregularly  along  each  interannular  seg- 
ment are  delicate  lines  or  fissures  which  seem  to  run 
obliquely  through  the  medullary  sheath  from  the  mem- 
brane on  the  surface  of  the  nerve-fibre  to  the  axis-cyl- 
inder. Their  significance  is  not  yet  determined  ;  they 
are  called  the  "  incisures  of  Schmidt."     (See  Fig.  4.) 

§  23.  The  complex  microscopic  structure  of  the  med- 
ullated  nerve-fibre,  as  described  above — outer  sheath, 
meduUai'y  sheath,  axis-cylinder,  interannular  segments 
limited  at  each  end  by  annular  constrictions,  nucleus 
and  nucleolus,  and  incisures  of  Schmidt — cannot  be 
considered  as  "ultimate,"  even  in  the  restricted  sense 
in  which  we  use  the  word  as  applied  to  what  the  eye 
can  see  by  the  aid  of  optical  instruments.  Other  still 
more  minute  characteristics  of  its  structure  must  be 
briefly  mentioned,  although  with  the  understanding 
that  their  interpretation,  and  even  their  existence,  is 
more  doubtful  than  are  the  characteristics  already  de- 
scribed. 

The  fact  that  isolated  axis-cylinders,  when  submitted 
to  the  action  of  picrocarminate  of  ammonia,  are  stained  red  along 
their  median  line,  while  an  extremely  thin  homogeneous  border  is 
left  comparatively  uncolored,  and  the  additional  fact  that  minute 
flakes  or  scales  sometimes  seem  to  appear  upon  their  surface,  have 
led  to  the  conjecture  that  the  axis-cylinder  has  a  double  structure. 
The  clear  homogeneous  border  probably  corresponds  to  the  so-called 
"sheath  of  Mauthner." ' 

The  "fibrillated"  appearance  of  the  axis-cylinder  under  the  mi- 
croscope has  already  been  referred  to  as  undoubted  ;  but  the  exact 
'  See  Ranvier,  Traite  Technique  d'Histologie,  i.,  pp.  738,  742. 


f-cy 


Fig.  5.— Medul- 
]ated  Nerve- 
tihre  from  the 
Sciatic  of  an 
Adult  Kahbit. 

«»»/!•  (E-an- 
vier.)  ff,  An- 
n  u  1  a  r  c  o  n- 
Btriction  ;  and 
c7/,  axis  -  cyl- 
i  n  d  e  r  with 
double  con- 
tour showing. 


DOUBLE   COIs^TOUR   OF    AXIS-CYLINDEE. 


39 


nature  and  the  interpretation  of  this  appearance  are  still  matters 
of  dispute.  On  account  of  the  fact  that  the  light  must  be  passed 
through  two  or  perhaps  three  cylinders  in  order  to  reach  the  inte- 
rior structure  of  the  nerve-fibre,  its  examination  under  the  high 
powers  of  the  microscope  which  are  necessary  to  see  this  fibrillated 
structure  is  extremely  difficult.  In  spite  of  this  difficulty,  however, 
Hans  Schultze  '  claims  that  the  fibrils  of  the  axis-cylinder  can  be 


Fig.  6.— Fibrillated  Appearance  of  the  Ajus-cylinders  of  Medullatecl  Nerve-fibres.  (Hans  Schultze.) 

distinctly  traced  in  hving  fibres,  when  these  are  in  process  of  form- 
ing and  are  still  naked,  or  where  they  issue  from  the  cells  without 
a  medullary  sheath,  or  where  they  lose  this  sheath  at  the  annular 
constrictions  or  in  the  peripheral  end-plexuses.  Various  prepara- 
tions of  dead  nerve-fibre,  treated  with  different  reagents,  seem  to 
demonstrate  the  same  fibrillated  structure.  Moreover,  from  the 
fact  that  the  nervous  substance  of  the  fibrils  takes  a  carmine  tinge, 
while  the  interfibrillary  nucleated  substance  remains  stained  steel- 
blue  with  the  nitrate  of  silver,  Schultze  argues  that  the  axis-cylinder 
consists  of  two  chemical  substances.  The  fibrillated  appearance 
can,  therefore,  scarcely  be  considered  as  due  to  the  arrangement  of 
'  In  the  Archiv  f.  Anat.  und  Physiol.,  1878,  Anat.  Abtli.,  pp.  259-285. 


40 


FOKM  OF  THE  NERVOUS  ELEMENTS. 


rows  of  granules  in  straight  lines.'  According  to  T.  W.  Engel- 
mann,'^  in  good  preparations  these  fibrils  appear  distinct,  and  are 
never  seen  to  anastomose  or  form  a  plexus  of  fibrils.  By  actual  count 
the  number  of  fibrils  remains  the  same — at  any  rate,  between  any 
two  annular  constrictions  ;  nor  are  they  apparently  interrupted  in 
their  course  by  these  constrictions.  The  fibrils,  as  found  in  different 
nerve-fibres,  seem  not  to  differ  in  respect  to  size  or  closeness  of 

contact,  but  their  number 
differs  in  nei've-fibres  of 
different  sizes.  Engel- 
mann  counted  about  four 
rHlinW  hundred  in  the  thickest 

fibres  taken  from  the  mo- 
tor roots  of  the  spinal 
cord  of  the  frog.  The 
closeness  of  their  contact, 
and  the  smallness  of  their 
number,  as  compared 
with  that  of  the  fibrils  into 
which  the  fibre  breaks  up 
at  its  peripheral  termina- 
tions, make  it  difiicult  to 
see  how  these  subdivi- 
sions of  the  axis-cylinder 
can  have  any  separate 
function  as  the  conduc- 
tors of  nervous  impulses. 
Further  information  I'e- 
garding  them  must  be  left 
to  subsequent  researches. 
(See  Fig.  6.) 

The  strict  continuity  of 
the  axis-cylinder  through 
the  annular  constrictions 
maybe  called  in  question. 
Engelmann  found  that,  on  being  treated  with  nitrate  of  silver,  the 
axis-cylinders,  as  a  rule,  were  broken  off  at  the  annular  constric- 
tions or  nodes.'  Out  of  a  hundred  cases  of  broken  cylinders  only 
four  appeared  where  they  had  not  parted  in  the  middle  of  these 
constrictions.  It  is  not  to  be  inferred  from  this,  however,  that  nor- 
mal and  living  nerve-fibres  are  interrupted  by  a  space  of  even  mi- 
'  So  article  of  H.  D.  Schmidt,  in  tlie  Monthly  Micr.  Jour.,  1874,  vol.  xii. 
'  Pfluger'B  Archiv,  xxii. ,  p.  36.  ^  PflUger's  Arcliiv,  xxii.,  pp.  1-24. 


Via.  7.— Fibrillated  Axis-cylinders  broken  at  the  Nodes 
of  Ranvier.     (Kngeimann.) 


THE   FIBRES   OF   REMAK. 


41 


croseopic  proportions  at  these  nodes  ;  no  such  interruption  appears. 
But  it  is  by  no  means  impossible  that  these  fibres  are  to  be  regarded 
as  composed  of  a  number  of  annular  segments  cemented  together — 
each  separate  fibril  placed  exactly  end  to  end  with  its  fellow  in  the 
adjoining  segments.  Such  an  arrangement 
would  accord  with  the  theory  which  regards 
the  segments  as  elongated  and  developed 
nerve-cells. 

§  24.  Non-meduUated  nerve-fibres,  or  fibres 
of  Be  male,  differ  from  those  already  described 
in  that  they  do  not  possess  a  medullary 
sheath.  They  are  grayish  and  translucent, 
longitudinally  striated,  with  flattened  elon- 
gated nuclei  lying  at  frequent  intervals  upon 
their  surface.  When  gathered  together  within 
a  sheath  of  neurilemma,  they  are  not  placed 
side  by  side  as  are  the  medullated  nerve- 
tubes  ;  they  are  rather  formed  in  the  interior 
of  the  nerve,  where  they  unite  and  divide  and 
make  an  intricate  plexus  or  network  of  fibres. 
They  are  grouped  in  larger  bundles,  some- 
times alone,  but  more  frequently  in  connec- 
tion with  medullated  fibres.  Their  striated 
appearance  is  probably  due  to  the  fact  that 
they,  like  the  axis-cylinder  of  the  medullated 
nerve-fibres,  are  composed  of  numerous  fibrils. 
As  has  already  been  said,  they  belong  to  the 
sympathetic  system. 

§  25.  The  size  of  different  nerve-fibres  in 
the  human  body  varies  greatly,  according  to 
their  kind,  position,  and,  perhaps,  function. 
As  a  rule  the  non  -  medullated  fibres  are 
smaller  than  the  medullated,  the  former  be- 
ing from  -g-oVo-  to  -g-oVo'  ^^  ^^  inch  in  diam- 
eter, and  the  latter  (in  the  trunk  and  branches  fig.  8.— Fibres  of  Remak  from 

„,,  Nj,  ^        ,  ,  „  ..  the    Pneumogastric    of    the 

oi  the  nerve)  trom  y^oo- to  g-gVo  ^i  an  inch.      nog.  "o/^.    (Ranvier.)   n, 

-o    J.  i.1  •  T      •  J.     1  i?   11  -I        T      ii  Nucleus    with    surrounding 

JtJut  this  rule  is  not  always  lollowed.  In  the  protoplasm,  p  ,•  6,  strise  cor° 
white  matter  of  the  cord  the  medullated  responding  to  fibrils. 
fibres  range  in  size  from  y^Vo-  ^^  ^  oVt  ^^  ^^  inch,  in  parts  of  the 
anterior  columns,  and  about  ,  oVt  of  an  inch  in  those  regions  of 
the  lateral  and  posterior  columns  which  are  nearest  the  gray  matter 
of  the  cord.  In  the  gray  matter  of  the  cord  and  brain  the  fibres  are 
much  finer — being  from  ^qVo  ^o  tt^o ¥  o^  ^^  i^^h  in  diameter,  or 


42         FOEM  OF  THE  NERVOUS  ELEMENTS- 

even  of  an  almost  immeasurable  fineness  ;  they  are  finest  of  all  in 
the  superficial  layers  of  the  brain  and  in  the  nerves  of  special  sense. 
In  some  instances  the  axis-cylinder  may  be  not  more  than  jo-oWo" 
of  an  inch  in  diameter. 

§  26.  The  number  of  fibres  which  enter  into  the  composition  of 
individual  nerves  also  varies  greatly.  In  the  common  motor  nerve 
of  the  tongue  it  has  been  estimated  at  about  five  thousand,  in  that 
of  the  eyes  at  fifteen  thousand,  in  the  optic  nerve  at  one  hundred 
thousand  at  least. 

§  27.  So-called  ganglion-cells,  or  nerve-cells,  are  the  second  of 
the  two  structural  elements  which  can  be  more  minutely  described 
as  undoubtedly  belonging  to  the  nervous  system.  These  bodies 
vary  greatly  in  size  and  shape,  but  they  all  show,  when  subjected 
to  microscopic  examination,  certain  well-recognized  common  charac- 
teristics. Nerve-cells  are  irregular  masses  of  protoplasm,  finely 
granular  and  delicately  striated,  with  a  large  nucleus  which  is  well- 
defined  and  vesicular  in  appearance,  and  which  usually  contains  a 
shining  nucleolus  ;  they  send  off  one  or  more  processes.  In  the  gray 
matter  of  the  cord  and  brain  they  are  embedded  in  the  neuroglia 
or  so-called  "  nerve-cement  ;  "  in  the  smaller  nervous  centres,  such 
as  the  ganglia  of  the  sympathetic  and  the  ganglia  on  the  posterior 
roots  of  the  spinal  cord,  they  are  surrounded  by  a  capsule  of  con- 
nective tissue. 

§  28.  Careful  microscopic  investigation  of  the  nerve-cell  with  high 
magnifying  powers  of  the  instrument  reveals  the  great  complexity 
of  its  structure.  In  describing  this  complex  structure  the  bipolar 
ganglion-cell  of  the  fish  may  be  considered  as  a  common  type.  Such 
a  cell  is  caUed  by  Max  Schultze  '  a  "  nucleated  swelling  of  the  axis- 
cylinder."  When  found  in  the  course  of  a  nerve-fibre  it  appears 
at  first  sight  as  a  complete  interruption  to  the  continuity  of  the 
fibre.  Further  examination  is  thought  to  show,  however,  that, 
when  the  fibre  reaches  the  cell,  the  axis-cylinder  loses  its  medul- 
lary sheath,  and  the  fibrils  which  constitute  the  substance  of  the 
cylinder  become  dissociated,  and  continue  their  course  over  the 
surface  of  the  "ganglionic  globe"  to  its  opposite  pole  ;  here  they 
reunite  and  form  a  fibre  identical  with  the  one  that  approached 
the  nearer  jDole  of  the  cell.  The  "ganglionic  globe  "  itself  appears 
to  be  composed  of  granular  substance.  We  may  distinguish,  then, 
in  such  a  ganglion-cell  these  two  parts  :  (1)  a  fibrillary  covering, 
the  fibrils  of  which  are  continuous  with  the  fibrils  of  the  axis- 
cylinder  on  either  side  of  the  cell ;  and  (2)  a  granular  globe  con- 
taining near  its  surface  a  nucleus,  within  which  one  or  more  nucleoli 
1  In  Strieker,  Human  and  Comparative  Histology,  i.,  p.  174. 


NERVE-CELL   FROM   SPINAL   GANGLION. 


43 


appear. '  A  repetition  of  these  parts  of  the  structure  of  the  bipolar 
cell,  it  is  claimed,  may  be  expected  and  found  in  ganglionic  nerve- 
cells  in  general. 

A  microscopic  structure  substantially  like  that  of  the  bipolar 
ganglion-cell  of  the  fish,  as  already  described, 
is  found  to  belong  to  the  multipolar  cells  of 
the  anterior  horns  of  the  spinal  cord  of  man, 
and  of  the  ox,  or  of  other  mammals.  Among 
the  many  processes  given  out  by  such  a  cell, 
the  researches  of  Deiters  and  of  others  have 
demonstrated  that  ordinarily  only  one  be- 
comes continuous  with  the  axis-cylinder  of  the 
peripherally  running  nerve-fibre.  This  one, 
called  the  -'prolongation  (or  process)  of  Dei- 
ters," has  sometimes  been  distinctly  seen  to 
be  fibrillated ;  and  it  is  supposed  that  its 
fibrils  are,  as  a  rule,  continuous  with  those 
of  the  axis-cylinder  of  the  nerve-fibi'e.  Hence 
it  is  called  the  "  axis-cylinder  process."  The 
other  processes  from  the  cell  also  seem  to  be 
fibrillar ;  but  the  quantity  of  interfibrillar 
granular  substance  which  they  contain  is 
greater  than  that  in  the  axis-cylinder  process. 
These  fibrils  ramify,  anastomose  with  each 
other,  and  become  lost  in  an  intricate  net- 
work of  extremely  minute  nervous  filaments. 
Over  the  surface  and  within  the  interior  of  the 
"  ganglionic  globe  "  of  the  multipolar  cell  the 
fibrils  of  all  these  processes  run  in  every  di- 
rection with  bewildering  complexity.  Their 
relation  to  one  another,  and  to  the  various 
parts  of  the  substance  of  the  cell,  cannot  be 
said  to  be  determined  with  any  degree  of  cer- 
tainty. Most  of  the  fibrils  appear  only  to  tra- 
verse the  ganglion-cells,  but  some  of  them, 
perhaps,  originate  within  the  cells.  In  the  case 
of  auy  thus  originating,  it  is  not  as  yet  possible  to  say  whether 
or  not  they  arise  out  of  the  nuclei  and  nucleoli,  and  so,  whether  we 
may  consider  these  parts  of  the  cells  as  the  special  sources  or  cen- 
tres of  the  nerve-fibrils,  asHarless,  Meynert,  and  others  have  done.^ 

'  See  Ranvier,  Traite  Technique  d'Histologie,  i. ,  p.  712. 

"  See,  on  this  whole  subject.  Max  Schultze  in  Strieker,  Human  and  Compara- 
tive Histology,  i.,  jip.  172-187  ;  Ranvier,  Traite  Technique  d'Histologie,  i.,  pp. 
710  if.  ;  and  Hans  Schultze,  Archiv  f.  Auat,  u.  Physiol.,  1878,  pp.  259-285. 


Fig.  9.— Nerve-cell  from  the 
Spinal  Ganglion  of  the 
Ray.  350/j,  (Ranvier.) 
my.  Medullary  sheath  of 
nerve-fibre,  enclosing  ca, 
the  axis-cylinder,  the  fi- 
brils of  vrhich  (/)  separate 
and  run  over  the  gangli- 
onic globe,  m;  n,  nii- 
cleus. 


44 


FORM  OF  THE  NERVOUS  ELEMENTS. 


§  29.  The  variety  of  shapes  taken  by  the  nerve-cells  has  already 
been  mentioned,  as  well  as  the  fact  that  they  may  be  classified  as 
unipolar,  bipolar,  and  multipolar.  Some  are  nearly  round  ;  others 
ovoidal,  caudate,  stellate,  or  shaped  like  a  flask  or  the  blade  of  a 
paddle.  Still  others  appear  somewhat  like  the  foot  of  an  animal 
with  claws  ;  while  the  branching  processes  of  others  give  them  the 
appearance  of  sprawling  out  irregularly  in  a  half-score  of  different 
directions.  To  a  certain  extent  the  shape  of  the  cells  is  character- 
istic of  that  region  of  the  central  nervous  system  where  they  are 


Pig.  10.— Multipolar  Ganglion-cell  from  the  Anterior  Horn  of  the  Gray  Substance  of  the  Spinal 
Cord  of  the  Ox.  (After  Deiters.)  1,  Nucleus ;  2,  axis-cylinder  process ;  3,  3,  branching 
processes. 

found,  in  most  abundant  numbers,  embedded  in  the  neuroglia. 
For  example,  large  ganglion-cells  of  irregular  shape,  with  branch- 
ing processes,  which  have  been  called  "  motor,"  are  found  in  the  ante- 
rior horns  of  the  gray  matter  of  tlie  spinal  cord  ;  pyramidal  cells  of 
various  sizes,  with  i^rocesses  from  both  base  and  apex,  are  character- 
istic of  the  cortex  of  the  cerebrum  ;  and  just  at  the  inner  edge  of 
the  gray  cortical  matter  in  the  cerebellum  appear  irregular  globu- 
lar or  ovoidal  cells,  which  send  off  one  or  two  branching  processes 
toward  the  surface  of  the  cerebrum.  The  ganglion-cells  of  the  sym- 
pathetic also  are  usually  globular  or  ovoidal,  and  have  one  or  more 
processes  which  pierce  their  capsule  and  become  non-medullated 


THE   GANGLION-CELL   AS   A   TYPE.  45 

nerve-fibres.  Uuipolar  cells  are  found  in  the  spinal  ganglia  of  tlie 
higher  animals,  bipolar  in  the  spinal  ganglia  of  fishes. 

Nerve-cells  vary  in  size  as  much  as  in  shape  ;  the  limits  may  per- 
haps be  given  as  from  about  ^|-q-  to  3-V0  °^  ^^  inch.'  No  special 
physiological  significance  can  in  any  case  be  assigned  to  the  shape 
of  the  nerve-cell ;  we  are  wholly  ignorant  of  the  meaning  of  such 
a  variety  of  forms,  and  of  the  value  of  any  particlar  form  in  a 
given  position.  It  is  possible,  however,  that  the  large  size  of  the 
so-called  "  motor-cells  "  of  the  anterior  horns  of  the  spinal  cord  is 
indicative  of  theii-  special  physiological  function.  We  may  also 
fairly  incline  to  interpret  the  multiplication  of  ganglion-cells  in  the 
central  parts  of  the  nervous  system  as  significant  of  the  large 
amount  and  high  quality  of  work  which  must  be  done  by  them 
within  these  centres.  It  is  possible  that  the  shape  of  the  cells  is 
largely  due  to  the  mechanical  conditions  which  control  their  de- 
velopment within  the  embryo  ;  but  upon  this  subject  we  have 
scarcely  any  trustworthy  information. 

§  30.  The  structure  of  the  nerve-fibres  and  nerve-cells,  and  the 
nature  of  the  histological  relations  which  apparently  exist  between 
the  two,  have  led  to  a  captivating  theory  intended  to  reduce  all  the 
elements  of  the  nervous  mechanism  to  modifications  of  a  single 
form.  Extremely  different  in  structure  as  the  various  parts  of  the 
nervous  system  obviously  are,  we  are  told  that  modern  histological 
science  refers  them  all,  for  their  elements,  to  "one  perfectly  defi- 
nite type  ; "  "  this  ty^De  is  the  ganglionic  nerve-cell.  The  important 
common  characteristic,  that  they  send  out  prolongations  which 
become  nerve-fibres,  is  assumed  to  belong  to  all  such  cells.  The 
fibres  are,  accordingly,  considered  to  be  prolongations  of  the  cells, 
and  to  be  formed  of  substance  like  that  of  the  source  from  which 
they  appear  to  arise.  Nerve-fibres  may  then  be  described  as  nerve- 
cells  drawn  out  into  an  extremely  long  peduncle,  which  serves  to 
connect  them  with  other  similar  cells  and  fibres,  or  with  certain 
muscular  fibres  which  the  nervous  matter  commands.  This  mor- 
phological theory  of  the  nervous  elements  rests,  however,  upon  a 
doubtful  basis,  and  certain  strong  objections  may  be  brought  against 
it.  We  are  probably  warranted  simply  in  asserting  that  both  classes 
of  these  elements,  Hke  the  other  primary  structural  forms  of  the 
body,  may  be  regarded  as  differentiations  of  one  type  (the  cell) 
under  conditions  of  which  we  are  almost  wholly  ignorant. 

There  is  accumulating  evidence  in  favor  of  the  view  that  nerve- 

^  See  an  article  of  J.  Hoffmann  in  the  American  Journal  of  Neurology  and 
Psychiatry,  August,  1883    pp.  432  ff. 

-  Eanvier,  Traite  Technique  d'Histologie,  i. ,  p.  710. 


46         rOKM  OF  THE  NEEYOUS  ELEMENTS. 

fibres  are,  in  general,  connected,  both  histologically  and  physiologi- 
cally, with  the  nerve-cells.  One  of  the  processes  of  each  cell  may, 
therefore,  as  a  rule,  be  regarded  as  continuous  with  the  axis-cylin- 
der of  a  nerve-fibre.  It  is  true  that  this  connection  can  by  no 
means  always  be  traced  by  the  microscope.  A  score  of  years  ago 
one  investigator '  declared  that,  after  having  examined  the  gray 
matter  of  the  spinal  cord  a  great  number  of  times,  he  had  demon- 
strated this  alleged  connection  only  very  rarely.  Kepeated  obser- 
vations since,  of  the  improved  modern  kind,  have  not  done  away 
with  the  comparative  infrequency  of  the  desired  demonstration. 
But  from  the  very  nature  of  the  case  a  great  number  of  the  nerve- 
fibres  must  have  their  connection  with  the  cells  broken  off  by  the 
treatment  they  receive  in  preparation  for  examination.  And  the 
positive  cases  where  such  connection  has  been  traced  may  fairly  be 
said  to  have  indicated  the  rule.  Moreover,  the  facts  of  physiology 
(to  which  reference  will  be  made  subsequently)  seem  to  favor  such 
a  view  of  the  anatomical  relation  of  these  two  elements  of  the  ner- 
vous system. 

Additional  evidence  upon  this  subject  may  perhaps  be  derived 
from  the  recent  researches  of  E.  A.  Birge.^  This  investigator  under- 
took the  gigantic  task  of  counting  the  nervous  elements  in  the  gan- 
glia and  roots  of  the  spinal  cord  of  a  large  number  of  frogs.  He 
apparently  discovered  a  general  relation  indicating  some  agreement 
in  the  number  of  the  so-called  motor-cells  and  the  fibres  alleged  to 
originate  from  these  cells.  In  one  case  (No.  42)  an  actual  count  of 
ten  motor-roots  gave  5,734  fibres  and  5,777  cells  on  the  right,  and 
5,740  cells  on  the  left  side  of  the  cord.  Other  results  of  counting, 
however,  were  by  no  means  so  favorable  to  the  statement  that  the 
number  of  the  fibres  in  the  roots  agrees  exactly  with  the  number  of 
cells  in  the  corresponding  x-egion  of  the  cord.  Nor  could  more 
complete  results  of  this  kind  form  any  sufficient  warrant  for  the 
conclusion  that  everywhere  in  the  nervous  system  the  number  of 
fibres  corresponds  with  the  cells,  or  that  the  nerve-fibres  all  spring 
from  the  nerve-cells  ;  much  less,  that  they  may  be  reduced  to  one 
form  of  such  cells  as  to  a  perfectly  definite  type. 

§  31.  The  discussion  of  the  chemical  constitution  and  structural 
form  of  the  elements  of  the  nervous  system  introduces  the  ques- 
tion as  to  the  Functions  of  these  Elements.  This  question  must 
be  answered,  if  at  all,  by  the  science  of  physiology.     And  in  view 

'  Vulpian,  see  Lemons  sur  la  Pliysiologie  du  Systeme  Nerveux,  p.  318,  Lect- 
ure of  July  9,  1864. ' 

'Archiv  f.  Anat.  u.  Physiol.,  1882,  Physiolog.  Abtli.,  pp.  435-479,  espe- 
cially p.  471. 


EXCITABILITY   AND   COISTDUCTIVITY.  47 

of  our  ignorance  of  the  genuine  nervous  character  of  all  other 
claimants  to  a  place  among  the  elem'ents  of  the  nervous  system,  our 
inquiry  is  narrowed  to  the  following  terms  :  What  can  nerve-fibres 
and  ganglionic  nerve-cells  do  ?  With  the  activities  of  these  ele- 
ments, as  combined  into  the  complex  organs  of  the  human  nervous 
mechanism,  the  whole  of  our  subsequent  examination  is  designed 
to  deal  We  speak  here  very  briefly  of  certain  fundamental  prop- 
erties of  the  two  nerve-elements  already  described — that  is,  of  .the 
nerve-fibres  as  gathered  into  bundles  called  nerves,  and  of  the  cells 
as  collected  into  ganglia  and  connected  with  these  nerves. 

Nerves  and  nerve-cells  have  certain  properties  in  common  ;  that 
is  to  say,  within  certain  limits  both  can  do  the  same  things.  Both 
are  capable  of  becoming  the  subjects  of  a  specific  kind  of  molecu. 
lar  motion  which  we  are  entitled  to  consider  as  distinctively  "  neu- 
ral"  but  about  whose  nature  and  mathematical  or  physical  relations 
to  other  modes  of  the  molecular  motion  of  matter  we  are  still  al- 
most totally  ignorant.  Both  are  also  capable  of  projDagating  this 
distinctively  "  neural  commotion  "  from  one  portion  of  their  struct- 
ure to  another.  In  a  word,  both  nerve-fibres  and  nerve-cells  have 
the  properties  of  Excitability  and  Conductivity  ;  and  the  excitation 
and  conduction  of  excitation  which  these  nervous  elements  display 
are  of  a  kind  peculiar  to  themselves.  It  is  the  production,  propa- 
gation, modification,  and  distribution  of  this  distinctive  nerve-com- 
motion which  constitutes  the  one  constant  function,  or  projDerty, 
of  the  nervous  elements,  whether  considered  as  isolated  or  as  com- 
bined into  organs.  It  is  customary  with  some  writers  to  speak  of 
the  production  of  psychical  phenomena  as  the  crowning  function 
of  the  nervous  system.  But  whatever  may  be  the  view  we  shall 
find  ourselves  compelled  to  take  of  the  relations  between  the  loca- 
tion, quantity,  quality,  and  combinations  of  this  neural  molecular 
motion  and  the  phenomena  of  self-conscious  life,  from  our  present 
point  of  view  the  utterances  of  such  writers — if  designed  as  anything 
other  than  figures  of  speech  which  need  to  be  explained  in  detail 
to  be  even  suggestive  of  those  real  facts  and  relations  which  they,  in 
truth,  only  symbolize — are  of  little  interest  or  value.  We  are  speak- 
ing of  a  material  structure,  which,  although  alive  and  standing  in 
altogether  unique  relations  to  psychical  phenomena,  is,  nevertheless, 
in  itself  considered,  nothing  but  a  very  complex  collection  of  moving 
molecules.  The  peculiar  form  of  molecular  motion  which  charac- 
terizes this  structure — namely,  so-called  "  nerve-commotion  " — is 
its  unique  function.  Inasmuch  as  such  nerve-commotion  may  be 
considered  as  originally  set  up  in  a  single  nervous  element  or  group 
of  elements,  and  then  propagated  from  this  initial  point  along  cer- 


48  FuisrcTioisr  of  the  itervous  elements. 

tain  more  or  less  definitely  marked  tracts  to  other  elements  oi 
groups  of  elements,  we  may  divide  the  one  function  into  two — the 
function  of  excitation  and  the  function  of  conduction. 

§  32.  Nerve-commotion,  or  neural  molecular  action,  is,  of  course, 
never  an  uncaused  event.  It  begins  at  certain  points  in  the  ner- 
vous elements,  where  it  is  set  agoing  by  the  application  of  appropri- 
ate causes  of  excitation.  The  causes  of  the  excitation  of  the  ner- 
vous elements  are  called  "stimuli."  Stimuli  are  of  two  general 
kinds — external  and  internal.  External  stimuli  comprise  all  such 
modes  of  the  motion  of  matter  as  act  upon  the  peripheral  parts  of  the 
nervous  system,  and  so  produce  wdthin  it  a  state  of  excitation  or 
nerve-commotion ;  among  these  are  light,  heat,  chemical  changes, 
etc.  Internal  stimuli  are  such  as  act  upon  the  nerve-cells  of  the 
central  organs  ;  they  consist,  in  general,  of  changes  in  the  blood 
produced  by  an  increase  or  decrease  of  oxygen,  the  presence  of 
drugs,  etc.  The  susceptibility  of  a  nerve  to  any  form  of  external 
stimulus  is  called  its  "  irritability  ; "  and  when  a  nerve  will  no 
longer  respond  to  such  stimulus  by  being  thrown  into  a  condition 
of  excitation,  it  is  said  to  have  lost  its  irritability.  As  the  word  is, 
generally  used,  then,  the  irritability  of  a  nerve  is  its  property'  of 
excitability  under  the  action  of  some  form  of  external  stimulus. 
When  excited  by  such  stimulus  it  is  said  to  be  irritated.  We  shall 
use  both  sets  of  words,  reserving  the  words  "  pynitn.tinn  "  and  "  ex- 
citabilitv"  for  the  gene^gLalaie  and  fuj^^^tJQ^  'sf  all  nervous  tissue 
considerecl  as  capable  of  a  specific  molecular  commotion  ' — a  nerve- 
commotion. 

§  33.  But  although  all  the  nervous  elements  may  be  said  to  have 
the  properties  of  neural  excitability  and  conductivity,  important 
difiierences  arise  as  to  the  conditions  under  which,  and  as  to  the 
modes  in  which,  they  exercise  their  functions  when  combined  into 
a  complex  nervous  system.  In  the  normal  condition  of  such  a  sys- 
tem it  is  by  no  means  all  of  its  parts  which  are  directly  excitable, 
whether  by  external  or  by  internal  stimuli ;  nor  is  the  efi'ect  of  the 
excitation  of  both  the  elementary  structural  forms  of  such  a  system 
exactly  the  same.  A  single  nerve  may,  indeed,  be  separated  from 
the  other  parts  of  the  nervous  system,  with  a  muscle  attached,  and 
may  then  be  made  to  exercise  its  neural  function  in  moving  the 
muscle  by  being  itself  stimulated  with  dififerent  kinds  of  stimuli  at 
different  points  along  its  course.  But  in  their  normal  place  and 
condition  nerves  are   never  excited  by  the  direct  application  of 

'  It  is  a  pity  that  we  have  in  English  no  one  word  which  can  be  nsed  under 
all  conditions,  and  compounded  ad  libitum^  in  order  to  designate  a  property,  a 
process,  a  state,  etc.,  as  can  the  German  word  Erregen,  Erregung,  etc. 


GAFGLION-CELLS   AS   DISTRIBUTOEY.  49 

stimuli ;  they  are  always  excited  indirectly  by  the  propagation  to 
them  of  nerve-commotion  which  originates  in  the  central  organs- or 
in  the  end-organs.     The  distinctive  office  of  the  nerves  is,  then,  to 
act  as  conductors  of  molecular  motion  set  up  in  themselves  by  the 
du-ect  excitation  of  the  nervous  elements  in  which  they  either  cen- 
trally or  peripherally  terminate.     Moreover,  large  portions  of  the 
central  organs  do  not  respond  to  the  direct  application  of  various 
kinds  of  stimuli  to  their  surface.     We  are  obliged,  then,  to  suppose 
that  many  of  the  nerve-cells  which  compose  these  organs  are  excita- 
ble only  by  stimulation  through  the  nerve-fibres  that  run  into  them. 
The  case  of  the  normal  nervous  system,  with  respect  to  its  excita- 
bility, may,  then,  be  briefly  described  in  the  following  terms  :  The 
end-organs  of  sense  are  directly  excitable  by  external  stimuli,  and 
each  specific  kind  of  end-organ  which  is  characteristic  of  a  particu- 
lar sense  is  excitable  only  by  the  specific  kind  of  stimuH  appropri- 
ate to  that  sense.     The  afferent  or  centripetal  nerves  are  excited 
only  by  the  end-organs  of  sense  ;  their  specific  function  is  to  con- 
duct the  nerve-commotion,  started  by  the  external  stimuli  in  these 
end-organs,  toward  the  central  organs.     The  efferent  or  centrifugal 
nerves  are  not  directly  excited  by  either  internal  or  external  stimuli, 
but  only  by  the  central  organs  ;  their  specific  function  is  to  conduct 
the  nerve-commotion  started  in  them  by  the  central  organs  to  the 
muscles,  glands,  etc.— to  the  peripheral  parts  of  the  body  which 
are  to  be  moved  through  their  excitation.     The  central  nerve-cells 
themselves  are  excited  either  through  the  nerve-commotion  brought 
to  them  by  the  afferent   nerves  or  by  internal  stimuli.     Nerve- 
commotions   are  also   said ,  to   arise  in   them    automatically  ;  but 
the  facts  covered  by  the  term  "  automatic  "  require  further  distinc- 
tions to  be  made  as  to  the  functional  activity  of  the  different  nerve- 
elements. 

§  34.  If  the  distinctive  normal  function  of  the  nerves  is  the  con- 
ducting of  neural  molecular  motion  between  the  central  organs 
and  the  end-organs,  the  function  of  the  ganglion-cells  can  by  no 
means  be  pronounced  so  simple.  These  cells  are,  indeed,  also  con- 
ductors of  nerve-commotion  ;  within  the  central  organs  they  form 
important  parts  of  the  tracts  along  which  such  commotion  passes. 
They  serve  also  as  points  for  the  division  and  redistribution  of  this 
commotion  ;  they  may  be  spoken  of  as  switching-places  in  the  sys- 
tem or  network  of  tracts.  In  these  "  shunting-places"  of  the  cell 
many  lines  of  conduction  meet ;  and  the  one  of  them  taken  by  any 
impulse  entering  the  ceil  may  depend  upon  the  relative  amount  of 
resistance  offered  by  these  Hues.  The  work  of  the  cell  may  then 
be  considered  as  "re-directive."  The  office  of  the  cell  in  distri- 
4 


50  ruNCTioisr  of  the  nervous  eleme]S"ts. 

bution  of  the  nerve-commotion  may  also  be  either  to  condense  or 
to  disperse  it ;  in  the  former  case  the  distribution  might  be  spoken 
spoken  of  as  "associative,"  in  the  latter  as  "dissociative."'  They 
may  also  intensify  or  diminish  the  nerve-commotion  entering  them. 
But  the  nerve-cells  have  also  other  functions,  or  forms  of  the  one 
neural  function,  which  have  been  classed  as  either  (a)  automatic, 
(6)  reflex,  or  (c)  inhibitory. 

(a.)  Automatism,  or  the  power  of  initiating  the  peculiar  form  of 
molecular  motion  known  as  "vital  impulses,"  independently  of 
the  action  of  any  discoverable  stimulus  from  without,  is  one  of  the 
fundamental  propei'ties  of  protoplasm.  An  amoeba,  for  example,  is  a 
minute  mass  of  such  protoplasm  ;  it  executes  movements  which  can- 
not be  wholly  explained  by  reference  to  any  changes  in  its  environ- 
ment. The  difficulty  of  distinguishing  automatic  from  reflex  action 
in  the  spinal  cord,  and  muscular  from  nervous  automatism  in  the 
sporadic  ganglia,  need  not  concern  us  at  present.  According  to 
Eckhard  "^  two  kinds  of  this  automatic  function  of  the  ganglion-cells 
may  be  distinguished — viz.,  the  automatic-tonic  and  the  automatic- 
rhythmic.  In  the  foi'mer  case  the  control  of  the  cells  over  the 
muscular  structvires  by  means  of  the  efferent  nerves  is  irregular ; 
in  the  latter  this  control  results  in  the  nearly  simultaneous  contrac- 
tion of  the  same  set  of  such  structures,  repeated  at  regular  intervals  ; 
as  is  the  case  in  the  movements  of  the  heart  and  lungs.  In  neither 
case,  however,  can  we  form  any  clear  conception  of  the  origin  within 
the  cells  of  this  neural  commotion,  of  the  nature  of  the  forces  at 
work  to  produce  it,  or  of  the  changes  in  material  that  are  involved 
in  it.  We  can  only  say  that  as  yet  we  know  no  reasons  lying  out- 
side of  the  structui-e  and  activities  of  the  living  nerve-cells  them- 
selves which  will  account  for  the  starting  of  the  excitation.  In  this 
sense,  at  least,  such  neural  action  is  "automatic." 

(6.)  The  reflex  function  of  the  ganglion-cells  admits  of  a  some- 
what more  detailed  and  satisfactory  statement ;  but  the  phenomena 
and  laws  of  reflex  nervous  action  are  properly  discussed  as  belong- 
ing to  the  central  organs  of  the  nervous  system.  It  is  enough,  at 
present,  to  note  that  the  great  changes  which  take  place  in  the 
character  of  nervous  impulses,  when,  after  entering  the  central 
organs  by  the  afferent  tracts,  they  are,  as  it  is  said,  "  reflected " 
from  those  organs  along  the  efferent  tracts,  are  indubitable  evi- 
dence of  the  specific  molecular  activity  of  the  ganglion-cells.  For 
the  afferent  impulses  are,  in  fact,  not  simply  reflected  in  these  cells ; 

'  See  A.  Hill,  Tlie  Plan  of  the  Central  Nervous  System,  p.  2.  Cambridge 
1885. 

'•^  Hermann's  Haudb.  d.  Physiol.,  II.,  ii.,  p.  19  f. 


GATS^GLIOIST-CELLS    AS   INHIBITORY.  51 

they  are  greatly  modified  as  to  their  number,  intensity,  character, 
and  distribution.  This  modification  is  proof  of  profound  molecu- 
lar changes  that  are  instituted  in  the  substance  of  the  cells  them- 
selves. It  is  one  proof,  among  others,  that  a  large  expenditure  of 
energy  in  the  cells  accompanies  the  transmutation  of  afferent  into 
efferent  impulses. 

(c.)  The  function  of  inhibition,  as  ascribed  to  ganglion-cells,  must 
be  pronounced  more  doubtful  in  character  than  either  of  the  two 
foregoing.  It  was  found  by  Wundt '  that  nervous  impulses  are 
delayed  on  passing  through  the  sj^inal  ganglion.  Such  impulses 
seem  also  to  consume  an  amount  of  time  in  travelling  along  or 
through  the  cord  that  cannot  readily  be  accounted  for  as  wholly 
due  to  the  length  of  the  nervous  tracts  which  they  thus  traverse. 
But  until  our  information  is  more  precise  as  to  the  microscopic 
structure  of  the  cord,  and  as  to  the  tracts  within  it  which  the  ner- 
vous impulses  follow,  we  cannot  say  with  confidence  how  much  of 
this  delay  is  due  to  molecular  changes  peculiar  to  the  cells  them- 
selves. That  the  automatic  and  reflex  functions  of  the  medulla 
oblongata  may  be  compounded,  as  it  were,  in  such  way  as  either  to 
inhibit  or  to  accelerate  the  action  of  the  heart  and  lungs  and  mus- 
cular walls  of  the  arteries,  is  a  well-known  fact.  It  has  already 
been  said  that  nerve-cells  may  diminish  as  well  as  intensify  the 
nerve-commotion  entering  them.  When  afferent  impulses  reach  the 
ganglion-cells  of  the  centres,  and  find  them  already  at  work,  such 
impulses  result,  according  to  circumstances,  in  either  inhibiting  or 
augmenting  this  activity.^  Moreover,  the  tone  given  forth  by  a 
muscle,  when  tetanized  by  stimulating  the  nerve  to  which  the  mus- 
cle is  attached  with  repeated  induction-shocks,  has  the  same  num- 
ber of  vibrations  per  second  as  there  are  of  such  shocks  ;  but  the 
tone  given  forth  by  muscle  tetanized  through  tlie  spinal  cord,  or 
by  action  of  the  will,  has  a  constant  number  of  vibrations,  namely, 
about  nineteen  per  second.  It  would  appear  from  this,  also,  that 
the  central  apparatus  of  nerve-cells  controls  the  impulses  which 
tetanize  the  muscle,  according  to  the  molecular  structiu-e  and 
changes  of  those  cells.  In  this  sense,  then,  the  cells  may  be  said 
to  exercise  inhibitory  functions  under  certain  conditions. 

§  35.  A  consideration  of  the  different  effects  produced  by  the 
conduction  of  nervous  impulses  along  the  different  nerves  of  the 
system  would  seem  at  first  to  justify  the  classification  of  the  nerves 
according  to  the  varieties  of  their  functional  activity.     In  this  way 

'  Untersuchungen  zur  Mechanik  der  Nerven,  1876,  Abth.  ii.,  pp.  45  ff. 
-  Comp.  Foster,  A  Text-book  of  Physiology,  fourth,  edition,  p.  134.     New 
York,  1«80. 


52  ruNCTiojsr  or  the  neevous  elements. 

we  should  distingiiisli  the  following  classes  :  (a)  nerves  of  motion 
controlling-  the  muscular  apparatus,  whether  of  smooth  or  of  striated 
muscular  fibres  ;  (6)  nerves  of  inhibition  ;  (c)  nerves  of  secretion  ; 
(d)  trophic  nerves,  or  nerves  which  have  a  direct  influence  upon  nu- 
trition ;  (e)  centripetal  nei-ves  that  have  no  sensory  function  ;  and, 
finally,  (/"")  sensory  nerves,  or  those  the  excitation  of  which  may 
result  in  conscious  sensation.' 

That  the  irritation  of  different  nerves  may  have  results  so  differ- 
ent as  are  indicated  by  the  foregoing  classes  must  indeed  be  ad- 
mitted ;  but  it  is  quite  another  question  whether  this  difference  is 
not  wholly  due  to  the  sources  of  origin  for  the  nerve-commotions 
sent  along  them,  and  to  the  structures  in  which  it  terminates,  rather 
than  to  any  difference  in  the  essential  physiological  function  of  the 
nerves  themselves.  Just  as  the  same  electrical  current  may  pass 
along  the  same  kind  of  wire,  and  write  a  message,  or  ring  a  bell,  or 
move  the  legs  of  a  frog  ;  just  so  the  irritation  of  certain  fibres  of  the 
pneumogastric  nerve  results  in  controlling  the  motion  of  the  heart ; 
the  ii'ritation  of  other  nerves  seems  to  have  an  immediate  metabohc 
effect  in  directing  the  secretory  processes  ;  that  of  still  others  pro- 
foundly modifies  the  nutrition  of  the  portions  of  the  body  to  which 
they  are  distributed.  All  these  effects  are  in  ajDpearance  greatly 
riulike  the  movement  of  a  muscle  under  stimulation  fi-om  a  nerve. 
With  regard  to  the  influence  of  the  nerves  on  nutrition  (then-  ^?-o- 
phic  function)  it  is  not  necessary,  in  order  to  account  for  it,  that 
some  specific  action  of  a  particular  kind  of  nerves  should  be  as- 
sumed. We  should  sup230se,  of  course,  that  the  chemical  j)rocesses 
in  which  nutrition  consists  would  be  changed  in  character  by  the 
molecular  changes  in  the  tissue  which  irritating  any  of  the  nerve- 
fibres  running  into  it  would  inevitably  bring  about. 

Further  consideration  of  the  six  possible  classes  of  nerves  given 
above  reveals  the  fact  that  they  may  all  be  reduced  to  two,  accord- 
ing to  the  direction  in  which  their  function  of  conducting  nerve- 
commotion  is  exercised.  The  first  four  conduct  it  outward  from 
the  nervous  centres,  and  are  therefore  called  "efferent;"  the  last 
two  conduct  it  inward  toward  the  nervous  centres,  and  are  there- 
fore called  "  afferent."  Into  these  two  kinds  all  nerves  are  custom- 
arily divided,  so  far  as  their  physiological  function  is  concerned. 

§  36.  The  further  question  now  arises,  W^hether  the  general  phy- 
siological function  of  these  two  jDrincipal  classes  of  nerves  differs  in 
kind  as  well  as  in  direction  ;  or  are  afferent  and  efferent  nerves  to 
be  identified  so  far  as  their  specific  neural  function  is  concerned  ? 
Inasmuch  as  every  nerve-fibre,  in  the  normal  condition  of  the  ner- 

'  Comp.  Sigmund  Mayer,  in  Hermauu,  Handb.  d.  Pliysiol.,  II.,  i.,  pp.  200  ft 


AFFERET^T   AT^D    EFFEEENT   NERVES.  63 

vous  system,  is  a  stretch  of  nervous  matter  between  two  termina- 
tions— a  point  of  origin  and  a  point  of  issue  for  the  state  of  excita- 
tion— it  might,  at  first,  seem  simpler  to  consider  it  as  intrinsically 
capable  of  propagating  nerve-commotion  in  one  direction  only.  It 
would  be  concluded,  then,  that  the  behavior  of  afferent  and  effer- 
ent nerves,  when  stimulated,  is  essentially  different  with  respect 
to  their  molecular  processes.  Certain  phenomena  are  sometimes 
urged  in  favor  of  such  a  conclusion. 

The  application  of  heat  to  an  efferent  (or  motor)  nerve  causes  no 
contraction  in  the  muscle  which  the  nerve  supplies  ;  heat  does  not 
appear  to  be  a  stimulus  of  such  nerves.  On  the  contrary,  Griitzner  ^ 
concluded  that  heating  the  different  kinds  of  afferent  nerves  to 
from  about  115°  to  125°  Fahr.  does  excite  them.  The  passage  of 
a  constant  current  along  an  efferent  nerve,  so  long  as  this  cur- 
rent does  not  suddenly  change  in  strength,  does  not  stimulate  this 
nerve  so  that  the  muscle  contracts  ;  but  such  a  current  does  excite 
nervous  impulses  in  a  sensory  nerve.  Moreover,  certain  chemical 
substances  are  said  to  act  as  stimuli  on  efferent  nerves  which  have 
no  such  effect  upon  sensory  nerves. 

On  the  other  hand,  the  rate  of  conduction  in  both  afferent  and 
efferent  fibres,  under  similar  conditions,  is  about  the  same.  The 
laws  which  evince  the  behavior  of  nerves  under  stimulation  by  elec- 
tricity, and  which  are  most  relied  upon  as  a  basis  for  a  mechanical 
theory  of  the  nervous  system,  are  largely  the  same  for  both  kinds 
of  fibres.  There  is  a  large  amount  of  scientific  information,  called 
"  general  physiology  of  the  nerves,"  which  looks  in  the  direction  of 
identifying  the  molecular  processes  in  the  two  classes  of  nerve- 
fibres.  This  is  true  in  particular  of  the  remarkable  phenomenon 
known  as  the  "negative  variation  "of  the  nerve-current.  More- 
over, the  marked  difference  (referred  to  above)  in  the  results  ob- 
tained by  stimulating  motor  nerves  on  the  one  hand,  and  sensory 
nerves  on  the  othei',  is  plainly,  to  a  great  extent,  due  to  the  differ- 
ence in  the  sources  of  the  stimulation  ;  the  former  are  excited  by 
the  central  organs,  the  latter  by  the  end-organs  of  sense.  The  mo- 
lecular structure  of  these  two  sets  of  organs,  and  their  consequent 
molecular  motion  when  acted  upon  by  the  appropriate  stimuli,  dif- 
fer widely  ;  we  do  not,  then,  need  to  assume  a  specific  difference 
in  the  function  of  the  connecting  nerve-strands  in  order  to  account 
for  a  marked  difference  in  the  results.  Thus  it  may  be  assumed 
that  molecular  disturbances,  which  would  be  quite  powerless  to  stir 
the  sluggish  muscle-fibres  when  transmitted  to  them  by  a  motor 
nerve,  would  occasion  profound  changes  in  the  more  sensitive 
'  Pflijger's  Arcliiv,  xvii.,  p.  215. 


54  FUNCTIOlSr    OF    THE    NERVOUS    ELEMENTS. 

structui^e  of  the  ganglion-cells  when  transmitted  to  the  latter  by  a 
sensory  nerve. 

Various  attempts  have  been  made  to  demonstrate,  experimen- 
tally, that  motor  and  sensory  nerves  can  perform  each  other's  func- 
tions. Such  experiments  have  not  yet  been  altogether  successful. 
They  consist,  in  general,  of  attempts  to  unite  by  healing  the  cen- 
tral part  of  a  divided  sensory  nerve  and  the  peripheral  part  of  a 
divided  motor  nerve,  and  then  to  show  that  the  nerve  thus  united 
discharges  certain  sensory  or  motor  functions,  as  the  case  may 
be.  Philipeaux  and  Vulpian,'  after  various  rather  unsuccessful 
attempts  of  Flourens,  Bidder,  Schiff,  and  others,  succeeded  in 
uniting  the  central  portion  of  the  liugual  (or  sensory  gustatory) 
nerve  of  young  dogs  with  the  peripheral  end  of  the  hypoglossal 
(motor  nerve  of  the  tongue)  on  the  same  side.  Stimulation  of  the 
lingual  nerve  above  the  point  of  union  then  produced  contractions 
in  the  hypoglossal  of  the  same  side,  and  that  even  when  the  lin- 
gual was  divided  high  up  so  as  to  preclude  any  reflex  action.  But 
the  action  obtained  was  found  to  be  apparently  due  to  the  dtorda 
(motor)  fibres  present  in  the  lingual.  In  1863  Bert  succeeded  in 
reversing  the  course  of  the  nerve-fibres  in  the  tail  of  a  rat,  by  bend- 
ing this  appendage  over  and  implanting  its  end  in  the  animal's 
back.  After  healing  had  taken  place,  the  transplanted  tail  was  cut 
off  near  its  origiu,  and  found  to  be  sensitive — of  course,  in  the  re- 
verse direction  of  the  nerve-fibres  from  the  natural  one.  This 
experiment  would  seem,  then,  to  show  that  sensory  nerve-fibres, 
when  reversed,  can  transmit  sensory  impulses  in  the  direction 
which  was  formerly  centrifugal.  The  experiments  of  Kiihne  '^  and 
others  upon  the  intramuscular  ramifications  of  the  nerve-fibres  in 
the  sartorius  muscle  of  the  frog  point  in  the  same  direction.  If 
the  broad  end  of  this  muscle  be  divided  by  a  longitudinal  slit  into 
a  forked  shape,  then  stimulation  of  one  of  the  two  tines  of  the  fork 
beyond  their  division  will  stimulate  the  fibrils  of  the  other  tine  ; 
that  is,  the  minute  twigs  of  the  motor  nerve  in  the  tine  which  is 
directly  stimulated  have  acted  centripetally,  and  the  excitation  has 
then  descended  the  twigs  of  the  other  tine. 

For  all  the  foregoing,  and  for  other  reasons,  we  seem  warranted 
in  assuming  that  there  is  no  such  specific  difference  in  the  func- 
tion of  the  two  kinds  of  nerves  as  is  dependent  upon  the  peculiar 
structure  or  molecular  processes  of  each  kind.     Both  afferent  and 

'  See  Vulpian,  Legons  sur  la  Thysiologie  du  Systi^me  Nerveux,  etc  ,  pp. 
274  ff.  ;  and  comp  the  remarks  of  Hermann,  Handb.  d.  Physiol.,  II.,  1.,  pp. 
lOflf.,  and  of  Foster,  Text-book  of  Physiology,  pp.  503-508. 

^  Archiv  f.  Auat.,  Physiol.,  etc.,  1859,  pp.  595  fE. 


PROPERTIES   OE   ALL   NERVES.  56 

efferent  nerves  are  probably  capable  of  the  same  kind  of  molecular 
commotion  called  nervo as  excitation,  and  of  conducting  this  commo- 
tion in  either  direction.  The  marked  difference  in  the  results  of  the 
exercise  of  this  function  in  the  two  cases  is  probably  due  chiefly  to 
the  difference  in  the  organs  from  which  the  excitation  of  the  nerve 
starts,  and  into  which  it  is  discharged.  With  respect  to  neural  mo- 
lecular disturbances,  all  nerves  are  excitable,  conductors  of  excita- 
tion, and  exciters  of  nerve-cells  and  muscle-fibres.  And  if  to  this 
description  we  add  the  statement  that  nerve-cells  can,  acting  auto- 
matically, originate  this  nerve-commotion,  can  modify  its  character 
profoundly  as  it  passes  through  them,  and  distribute  it  in  various 
directions,  we  state,  in  the  most  general  form,  w^hat  is  at  present 
known  as  to  the  functions  of  the  nervous  elements. 


CHAPTER   II. 

COMBINATION  OF  THE  NEEVOUS  ELEMENTS  INTO  A 

SYSTEM. 

§  1.  In  the  last  chapter  the  nervous  elements  were  considered,  as 
far  as  possible,  without  reference  to  their  combination  for  the  ac- 
complishment of  a  common  work.  Regarded  as  isolated,  and  as 
possessed  only  of  those  properties  which  belong  to  all  living  mat- 
ter of  the  peculiar  chemical  constitution  and  structural  form  which 
are  described  by  the  word  "nervous,"  these  elements  are  of  great 
interest  to  physiological  and  psycho-physical  researches.  But  in 
their  normal  position  and  activity  the  nerve-fibres  and  nerve-cells 
are  always  combined  into  certain  organs,  which  are  then  arranged 
in  a  symmetrical  whole.  Thus  combined  they  are  dependent  upon 
each  other  for  the  parts  which  they  play  in  the  entire  s^'stem.  The 
condition  and  function  of  each  element  are  thus  determined  by  the 
condition  and  function  of  the  rest.  One  part  of  this  system  excites 
another,  or  modifies  the  excitation  received  from  another.  We  are 
unable  to  isolate  perfectly  any  one  of  these  elements,  and  so  study 
its  normal  functions  apart.  It  is,  indeed,  possible  to  dissect  out  a 
nerve  with  a  muscle  attached,  to  keejj  it  alive  for  a  time,  and  thus 
to  inquire  what  an  isolated  nerve  will  do.  In  this  way  many  of  the 
most  important  discoveries  in  the  general  physiology  of  the  nerves 
have  been  made.  But  every  nerve  is  itself  a  compound  of  nervous 
elements  which  have  been  placed  for  purposes  of  experiment  under 
abnormal  conditions.  The  action  of  the  nerve-cells,  even  when 
gathered  into  small  masses  called  ganglia,  is  not  open  to  direct  in- 
spection. Moreover,  when  different  tracts  of  nerves,  or  different 
regions  in  the  central  organs  where  ganglion-cells  abound,  are  par- 
tially isolated  by  being  laid  bare  for  the  direct  application  of  stimu- 
lus, just  so  far  as  they  are  separated  from  the  system  they  are  in 
abnormal  condition  and  show  abnormal  results  ;  and  just  so  far  as 
they  are  normal  in  condition  and  function  they  are  still  connected 
with  the  system.  It  is  the  mutual  condition  and  reciprocal  action 
of  the  elements,  when  combined  into  this  totality,  which  constitute 


MECHANISM   OF   THE  AMCEBA.  57 

the  nervous  mechanism.  A  brief  description  of  the  manner  of  this 
combination  is,  then,  indispensable  at  this  point. 

§  2.  It  will  be  of  great  service  toward  understanding  such  a  de- 
sci'iption  if  it  is  begun  under  the  guidance  of  some  appropriate  idea. 
Nerve-fibres  and  nerve-cells  exist  in  enormous  numbers  within  the 
human  nervous  system,  and  are  combined  in  different  proportions 
to  make  the  different  organs  of  this  system.  The  significance  of 
the  combination  appears  only  in  the  light  of  reflection  upon  the 
amount  and  kind  of  work  which  is  to  be  done.  The  office  of  the 
nervous  mechanism  has  been  said  (p.  18  f.)  to  be  that  of  "  concate- 
nating "  all  the  functions  of  the  living  body  in  accordance  with  the 
complex  internal  and  external  conditions  to  which  it  is  subject. 
But  in  the  case  of  any  of  the  higher  animals,  and  especially  in  the 
case  of  man,  this  one  office  requires  the  doing  of  a  quantity  and 
variety  of  work  that  are  proportionate  to  the  complexity  of  these 
conditions.  How  shall  such  a  quantity  and  variety  of  work  be  done  ? 
To  answer  this  question  may  be  said — speaking  figuratively — to  be 
the  problem  before  the  nervous  system.  The  actual  arrangement 
of  the  elements  of  this  system,  in  the  exercise  of  their  reciprocally 
conditioned  activities,  is  the  solution  of  the  problem.  As  in  all 
very  complex  questions  of  this  sort,  so  this  particular  problem  is 
solved  by  a  wise  division  of  labor. 

The  manner  in  which  the  human  nervous  mechanism  is  developed 
as  a  response  to  the  before-mentioned  problem  is  made  clear  by  con- 
sidering, in  the  first  place,  a  much  simpler  form  of  the  same  prob- 
lem. The  simple  protoplasmic  speck  called  an  amoeba  may  be  con- 
sidered as  a  living  molecular  mechanism.  It  appears,  even  under 
the  higher  powers  of  the  microscope,  as  almost  wholly,  if  not  quite, 
composed  of  undifferentiated  protoplasm,  in  the  midst  of  which,  as 
a  rule,  lies  a  single  nucleus.  If  differentiated  at  all,  it  may  be  ob- 
served to  have  a  somewhat  solid  external  layer,  called  an  ectosarc, 
and  a  more  fluid  granular  interior,  called  endosarc.  But  minute 
and  almost  structureless  as  it  appears,  the  amoeba  is  really  com- 
posed of  a  great  number  of  molecules  that  are  undergoing  constant 
change  ;  and  it  is  capable  of  exercising  several  wonderful  functions 
that  do  not  belong  to  any  non-living  collection  of  molecules.  Its  sub- 
stance is  metabolic,  respiratory,  reproductive.  The  protoplasm  of 
the  amoeba  is  the  subject  of  constant  chemical  alterations,  by  which 
the  old  protoplasm  is  broken  up  and  its  products  cast  off,  while 
new  protoplasm  is  formed.  Oxygen  is  assumed  by  this  substance 
and  carbonic  acid  excreted.  The  unit  which  is  constituted  by  the 
amoeba  may,  by  fission  (or  by  other  means),  divide  into  two  parts, 
Bach  of  which  becomes  a  fresh  unit.     But  more  important  for  our 


58  PLAN   OF   A   NERVOUS   SYSTEM. 

purpose  is  the  fact  that  the  amoeba  is  irritable  aacl  automatic.  It 
is  almost  unceasingly  in  motion.  It  is  living  matter  ;  and  when 
acted  on  by  stimuli,  it  suffers  an  explosion  of  energy  which  gener- 
ally results  in  a  change  of  place  and  form.  Inasmuch  as  these  pe- 
culiar "  amoeboid  "  movements  seem  substantially  identical  with 
those  which  occur  in  a  muscle  and  result  in  its  contraction,  the 
animalcule  may  be  said  to  be  contractile.  But  inasmuch  as  some 
of  these  movements  cannot  be  ascribed  to  irritation  of  the  external 
molecules  of  the  amoeba  by  the  surrounding  medium,  but  seem 
rather  to  be  due  to  energy  set  fi'ee  in  consequence  of  unknown  in- 
ternal changes,  we  call  it  automatic.  We  say,  "  it  has  a  will  of  its 
own."  Thus  does  the  molecular  mechanism  of  this  small  bit  of 
protoplasm,  under  the  stimulus  of  changes  in  the  pressure  and 
temperature  of  its  medium,  and  in  accordance  with  the  unknown 
laws  of  its  internal  self -originating  changes,  solve  the  problem  pre- 
sented to  it. 

Let  it  be  supposed  that  the  problem  becomes  more  complicated, 
and  the  animal  structure  which  is  to  solve  it  correspondingly  com- 
plex. The  metabolic  function  of  the  animal  may  then  be  assigned 
to  a  separate  system  of  structui'es ;  and  the  closely  related  secretory 
and  excretory  functions  as  well.  The  reproductive  function  may 
then  also  acquire  its  own  peculiar  organs.  The  muscles  perform 
movements  in  masses  because  they  retain  in  an  eminent  degree  the 
"  amoeboid  "  contractility.  But  the  property  of  being  irritable  and 
automatic  becomes  the  special  endowment  of  the  nervous  system. 
All  these  different  systems,  in  order  that  they  may  be  moved  in 
united  masses,  are  then  adjusted  to  a  mechanical  framework  (of  in- 
different value  so  far  as  really  vital  changes  are  concerned)  of  carti- 
lage, bone,  etc. 

But  the  eminently  irritable  and  automatic  system  of  molecules 
called  nervous  must  undergo  a  further  differentiation  of  function. 
In  the  structureless  protoplasm  of  the  amoeba,  the  external  mole- 
cules are,  of  course,  the  ones  primarily  to  be  affected  by  the  exter- 
nal stimuli.  It  is  with  the  intei'nal  molecules,  on  the  other  hand, 
that  the  changes  called  "  automatic  "  begin.  But  the  continual 
flux  of  its  protoplasmic  substance  indicates  that,  in  its  simplest 
form,  any  of  the  molecules  of  the  animalcule  may  in  turn  act  either 
as  irritable  or  as  automatic.  The  primary  differentiation  of  this 
substance  into  ectosarc  and  endosarc  points,  however,  to  a  division 
of  labor. 

By  this  primary  differentiation  of  the  substance  of  the  animal, 
one  cell,  or  group  of  cells,  becomes  more  eminently  irritable, 
another  automatic.     The  former  has  thus  been  fitted  for  the  spe- 


,     TRIPLE   FORM   OF   THE   SYSTEM.  59 

cial  work  of  responding  to  external  stimuli  by  vital  impulses  ; 
the  latter  for  that  of  initiating  so-called  automatic  impulses.  The 
position  of  the  former  in  the  animal  mechanism  will  then  natu- 
rally be  at  the  surface,  where  it  can  be  acted  upon  by  the  appro- 
priate external  stimuli ;  the  position  of  the  latter  will  naturally  be 
withdrawn  from  the  surface,  where  it  can  be  protected  from  such 
stimuli  and  left  undisturbed  for  action  that  is  either  automatic 
or  excited  by  only  internal  stimuli.  But  if  the  two  kinds  of  sub- 
stance are  to  perform  one  work,  although  by  division  of  labor, 
they  must  be  connected ;  that  is,  the  eminently  irritable  protojDlasm 
of  the  surface  must  be  joined  by  irritable  protoplasmic  material 
with  the  eminently  automatic  protoplasm  of  the  interior.  Three 
sets  of  organs  are  then  called  for  in  this  rudimentary  differentiation 
of  the  nervous  substance  :  (1)  superficial  cells  susceptible  to  exter- 
nal stimuli ;  (2)  central  and  eminently  automatic  cells,  also  suscep- 
tible to  internal  stimuli ;  (3)  a  strand  of  irritable  protoplasm  con- 
necting the  two. 

Yet  one  more  step  in  the  distribution  of  functions  between  the 
irritable  and  the  automatic  protoplasm  of  the  complex  animal  or- 
ganism must  be  taken,  in  order  to  reach  the  fundamental  triple  ar- 
rangement of  a  nervous  system.  The  system  of  eminently  contrac- 
tile tissue  called  muscular  must  be  brought  into  connection  with  the 
parts  already  described.  In  order  that  the  more  highly  organized 
animal  may,  like  the  amoeba,  both  have  and  exercise  "  a  will  of  its 
own,"  certain  of  its  muscle-fibres  must  be  placed  under  the  control 
of  the  central  and  automatic  cells.  In  order,  also,  that  the  entire 
muscular  system  may  feel  the  reflex  influence  of  external  stimuli, 
and  so,  by  co-ordinated  contractions  adapt  the  organs  of  the  body 
to  the  changes  of  its  environment,  the  muscle-fibres  must  be  indi- 
rectly connected,  through  the  automatic  cells,  with  such  superficial 
cells  as  are  sensitive  to  these  stimuli.  The  nervous  system,  there- 
fore, in  its  most  fundamental  form  consists  of  these  three  sets  of 
contrivances  with  their  respective  functions :  (A)  sensitive  cells 
upon  the  surface  of  the  body  ;  (B)  central  cells  that  are  both  auto- 
matic and  modifiers  and  distributers  of  sensory  impulses;  (C)  con- 
necting cords,  or  strands,  that  can  convey  the  nervous  impulses 
either  centripetally  from  A  to  B,  or  centrifugally  from  B  to  the  con- 
tractile muscular  tissues  of  the  body. 

Higher  developments  of  this  triple-formed  fundamental  type  of 
a  nervous  system  are  reached  by  further  differentiations  of  A,  B, 
and  G.  If  various  kinds  of  stimuli  are  to  act  upon  this  system, 
then  the  sensitive  cells  upon  the  surface  {A)  must  be  modified  into 
various  external  organs  of  sense :  and  with  these  organs  the  ter- 


60  PLAN   OF   A   NERVOUS   SYSTEM. 

minations  of  the  centripetal  or  sensory  nei'vous  strands  must  be 
variously  connected.  The  terminations  of  the  centrifugal  or  motor 
nervous  strands  may  also  be  variously  modified  so  as  to  connect 
■with  and  control  the  contractile  tissue  of  many  sets  of  muscles. 
The  central  cells  may  be  variously  grouped  and  arranged,  with 
functions  more  or  less  localized,  so  as  to  receive,  modify,  and  dis- 
tribute, in  manifold  ways,  the  diiferent  sensory  impulses  ;  and  so 
as  to  co-ordinate  these  impulses  for  definite  results  in  the  periph- 
eral parts  of  the  body.  Other  such  central  cells  may  become  more 
particularly  related  to  the  phenomena  of  conscious  sensation  and 
volition.  Such  a  highly  developed  nervous  system  will  then  con- 
sist of  the  following  parts  :  (^4)  End-organs  of  Sense,  like  the  skin, 
the  eye,  and  the  ear  ;  {A')  End-organs  of  Motion,  like  the  so-called 
motor  end-plates  and  terminal  nerve-bulbs ;  (B)  Central  Organs, 
like  the  various  peripheral  and  sjDoradic  ganglia,  the  spinal  cord, 
and  brain,  in  which  may  come  to  exist  (6)  certain  portions  more 
distinctively  automatic,  (&')  certain  others  more  concerned  in  re- 
ceiving and  distributing  reflexly  the  sensory  impulses,  and  (6")  still 
others  more  particularly  connected  with  the  phenomena  of  con- 
sciousness ;  and  (G)  Conducting  Nerves,  which  will  be  either  (c) 
centripetal,  afferent,  and  sensory,  or  (c')  centrifugal,  efferent,  and 
motor,  designed  to  connect  the  central  organs  and  the  end-organs. 
We  are  now  to  consider  the  details  with  which  such  a  highly  de- 
veloped nervous  system  is  actually  constructed  in  the  case  of  man. 
Our  guides  will,  of  course,  be  anatomy  and  histology. 

§  3.  In  the  manner  already  described  (Chapter  I.,  §  19)  the  indi- 
vidual nerve-fibres  are  collected  and  bound  together  in  fascicles  or 
groups  of  fascicles,  called  nerves,  and  in  larger  bundles  or  nerve- 
trunks.  The  nerve-cells  are  grouped  into  minute  masses  of  nervous 
matter,  such  as  the  sporadic  ganglia  found  in  the  sinus,  auricular 
walls,  and  auriculo-ventricular  groove  of  the  heart ;  or  they  are 
gathered  into  larger  bodies,  intersected  with  most  intricate  ramifi- 
cations of  the  nerves  and  intersi^ersed  with  the  finely  granular  sub- 
stance called  neuroglia,  such  as  constitute  the  various  parts  of  the 
brain  and  spinal  cord. 

§  4.  The  nerves  and  ganglionic  masses  of  nervous  matter  in  the 
human  body  are  arranged  in  two  great  systems,  the  Sympathetic 
and  the  Cerebro-spinal.  The  Sympathetic  Nervous  System  consists 
of  a  pair  of  nervous  cords,  situated  one  on  each  side  of  the  spinal 
column  ;  of  three  main  plexuses,  situated  in  the  cavities  of  the 
thorax  and  abdomen  ;  of  a  great  number  of  smaller  ganglia,  lying 
in  relation  with  the  viscera  of  the  same  cavities,  and  widely  distrib- 
uted over  the  body,  especially  in  connection  with  the  vascular  sys< 


GANGLIA   OF   THE   SYMPATHETIC.  61 

tem  ;  and  of  a  great  multitude  of  fine  distributory  nerves.  Each 
of  the  two  cords  consists  of  a  number  of  gangHa  united  by  interme- 
diate nerves.  In  the  other  regions  of  the  spinal  column  the  num- 
ber of  these  ganglia  equals  that  of  the  vertebra)  (sacral  5,  lumbar 
5,  thoracic  or  dorsal  12),  but  in  the  neck  (cervical)  there  are  only 
3.  From  this  ganglia  ted  cord  a  communicating  and  a  distribu- 
tory series  of  nerve-branches  are  derived.  By  the  communicating 
branches — each  of  which  contains  not  only  non-meduUated  nerve- 
fibres  from  the  sympathetic  system  to  the  cerebro-spinal  nerves, 
but  also  meduUated  fibres  from  the  cerebro-spinal  to  the  sympa- 
thetic— the  two  systems  are  brought  into  close  anatomical  and 
physiological  relation,  and  a  kind  of  double  interchange  takes  place 
between  them.  The  distributory  branches  of  nerves  in  the  sympa- 
thetic system  bring  the  gangiiated  cord  into  connection  with  the 
blood-vessels  and  viscera  of  the  body.  The  involuntary  muscles 
in  the  coats  of  these  vessels  and  in  the  walls  of  the  viscera  are 
thus  bound  together,  and  through  the  sympathetic  fibres  brought 
under  the  control  of  the  cerebro-siDinal  axis.  The  three  main  plex- 
uses referred  to  are  collections  of  nerve-cells  and  a  dense  plexiform 
arrangement  of  nerve-fibres.  One  of  them  is  situated  at  the  base 
of  the  heart,  to  which  it  gives  off  branches  that  wind  around  that 
organ  and  penetrate  its  muscular  substance  ;  another  is  placed  at 
the  upper  part  of  the  abdominal  cavity,  and  gives  origin  to  numei-- 
ous  plexiform  branches  that  supply  the  viscera  of  the  abdomen  ; 
the  third  is  in  front  of  the  last  lumbar  vertebra,  and  supplies  the 
vaso-motor  nerves  and  nerves  of  the  muscular  coats  and  mucous 
membranes  of  the  various  organs  in  that  region  of  the  body.  Fur- 
ther details  in  the  anatomy  of  the  sympathetic  nervous  system  are 
of  little  interest  to  psycho-physical  studies.  To  such  studies  it  is 
of  great  interest,  however,  to  know  that  this  system  forms  a  bond 
between  the  sensations,  emotions,  and  ideas  which  have  their 
physical  basis  in  the  molecular  condition  of  the  cerebro-spinal 
centres,  and  those  various  organs  in  the  thoracic  and  abdominal 
regions  whose  condition  is  so  closely  related  to  such  psychical 
states.  The  effect  of  certain  emotions,  for  example,  upon  the  con- 
dition of  the  circulation,  digestion,  etc.,  is  too  well  known  to  re- 
quire a  lengthy  statement. 

§  5.  The  Brain  and  Spinal  Cord  are  the  great  centres  of  the  cere- 
bro-spinal system.  These  bodies  are  situated  in  the  bony  cavity  of 
the  skull  and  spinal  column.  They  have  three  Coverings  or  Mem- 
branes, the  innermost  one  of  which  is  directly  united  with  the  sur- 
face of  the  nervous  substance,  and  sends  numerous  processes  into 
its  interior.      (1)  The  Dura  Mater,  which  is  the  membrane  lying 


Fig.  11.— View  of  the  Cerebro-spinal  Axis. 
(After  Bourgery.)  '/j.  The  right  half  of  the 
cranium  and  trunk  has  been  removed,  and 
the  roots  of  the  spinal  nerves  dissected  out 
and  laid  on  their  several  vertebrte.  P,  T,  O, 
cerebrum  ;  C,  cerebellum  ;  P,  pons  Varolii ; 
in  o,  medulla  oblongata  ;  m  «,  m  s,  upper  and 
lower  extremities  of  the  spinal  marrow.  CI. 
to  CVIII.  are  cervical  nerves ;  DI.  to  DXII., 
dor!=al  ;  LI.  to  LV.,  lumbar :  SI.  to  SV.,  sa- 
cral :  Col.,  coccygeal. 


PROCESSES   OF   THE  DUEA   MATER. 


63 


next  to  the  wall  of  the  bony  cavity,  is  tough,  white,  fibrous,  and  of 
structure  somewhat  different  in  the  cranial  from  the  spinal  cavity. 
In  the  former  position  it  is  identical  with  the  inner  periosteum  of 
the  bones  of  the  skull  ;  on  passing  into  the  spinal  column,  how- 
ever, the  periosteum  divides  into  two  or  more  lamellse,  the  inner- 
most of  which  is  prolonged  into  the  cylindrical  tube  that  includes 
the  spinal  cord.  Three  processes  of  the  dura  mater  divide — only 
incompletely — the  cavity  of  the  skull  into  two  symmetrical  halves 
and  into  an  upper  and  lower  space  :  (a)  the /ate  cerebri,  a  sickle- 
shaped  process  between  the  two  hemispheres  of  the  large  brain ; 


Fro.  12. — The  Cranium  opened  to  show  the  Falx  Cerebri  and  Tentorium  Cerebelli,  and  the  Places 
of  Exit  for  the  Cranial  Blood-vessels.  }4.  (Schwalbe.)  a,  a,  Falx  ;  6,  b,  the  tentorium :  3,  3, 
Sinus  transversu.'!,  and  2  to  3,  Sinus  rectus,  receiving  from  in  front  the  Vena  magna  Galena. 
4,  internal  jugular  vein  ;  5,  superficial  temporal  vein  ;  and  6,  middle  temporal  vein. 

(b)  the  falx  cerebelli,  a  similar  process  between  the  two  lateral  lobes 
of  the  cerebellum,  or  small  brain  ;  and  (c)  the  tentorium  cerebelli, 
an  arched  process  over  the  cerebellum  separating  it  fi'om  the  back 
portions  of  the  large  brain.  The  fluid  necessary  to  fill  up  the  gaps 
and  smooth  over  the  surfaces  of  the  closed  area  made  by  the  dura 
mater  is  contained  in  the  intercommunicating  spaces  of  the  mem- 
brane lying  next  inward  and  called  (2)  Arachnoid  ;  this  membrane 
is  transparent  and  of  delicate  connective  tissue.  Toward  the  dura 
mater  it  presents  a  smooth,  firm  surface,  like  that  of  a  serous  mem- 
brane, and  is  covered  by  a  layer  of  scaly  endothelium  ;  this  layer 
is  reflected  on  to  the  roots  of  the  spinal  and  cranial  nerves,  and 
becomes  continuous  with  the  lining  of  the  dura  mater  when  the 


64  THE   SPINAL   COED. 

nerves  pierce  the  latter  membrane.  The  space  below  this  surface 
is  called  subarachnoid  ;  the  subarachnoid  or  cerebro-spinal  fluid  (al- 
ready referred  to  as  filling  the  intercommunicating  compartments 
into  which  this  space  is  divided  by  bundles  of  delicate  areolar  tis- 
sue) is  alkaline  and  poor  in  albumen.  (3)  The  Pia  Mater  is  a  vas- 
cular membrane,  a  minute  network  of  fine  branches  of  arteries 
and  veins  held  together  by  delicate  connective  tissue.  These  rami- 
fications of  the  blood-vessels  in  the  pia  mater  are  on  their  way  to 
or  from  the  nervous  substance  of  the  spinal  cord  and  brain.  The 
membrane,  therefore,  closely  invests  this  substance,  being,  how- 
ever, more  intimately  attached  to  the  cord  than  to  the  brain.  Un- 
like the  arachnoid  membrane,  the  pia  mater  dips  into  the  fissures 
between  the  convolutions  of  the  cerebrum.  It  also  sends  its  pro- 
longations, not  only  into  the  fissures  of  the  cord,  but  also,  as  slen- 
der bands  (trabeculce)  from  its  inner  surface,  into  the  columns  of  the 
cord.  These  trabeculse  branch  and  anastomose  within  the  white 
substance  of  the  cord  hke  the  midrib  of  a  leaf.  The  pia  mater 
is  well  supplied  with  nerves. 

By  these  three  membranes  the  nervous  masses  of  the  cerebro- 
spinal system  are  protected,  held  together  and  in  place  with  a  soft 
and  yielding  but  sufficiently  firm  pressure,  and  nourished  by  the 
blood.  This  great  nervous  system,  as  a  whole,  consists  of  the  cen- 
tral organs — spinal  cord  and  brain — and  of  various  roots,  divisions, 
and  branches  of  spinal  and  cranial,  or  encephalic  nerves. 

§  6.  The  Spinal  Cord,  or  Medulla  Spinalis,  extends  in  the  spinal 
canal  from  the  aj)erture  in  the  cranial  cavity  [foramen  magnum), 
above  which  it  is  continuous  with  the  medulla  oblongata,  down- 
ward to  opposite  the  body  of  the  first  lumbar  vertebra,  where,  after 
tapering  ofij  it  is  s]3un  out  into  a  slender  thread  of  gray  nervous 
substance  [filuni  ierminale)  that  lies  in  the  axis  of  the  sacral  canal. 
Its  length  is  from  fifteen  to  eighteen  inches  ;  its  weight,  when  di- 
vested of  membranes  and  nerves,  about  an  ounce  and  a  half,  or  not 
far  from  one  thirty-third  of  that  of  the  brain.  It  is  nearly  cylin- 
drical in  shape,  its  front  and  back  surfaces  being  somewhat  flat- 
tened ;  it  has  two  considerable  enlargements  of  its  girth — an  up- 
per (cervical),  from  which  arise  the  nerves  that  supply  the  upper 
limbs  ;  and  a  lower  (lumbar),  which  supplies  the  lower  limbs  with 
nerves. 

§  7.  The  external  structure  of  the  spinal  cord  requires  us  to  no- 
tice (1)  the  Fissures  which  almost  completely  divide  it  for  its  whole 
length  into  right  and  left  (lateral)  halves,  and  are,  therefore,  fitly 
called  "  median  ; "  of  these  fissures  (a)  the  one  in  front  {anterior 
median)  is  somewhat  broader  than  (6)  the  one  behind  (posterior 


1-8 


40- 


Fig  13  —A.  Anterior,  anri  B,  Posterior.  View  of  the 
Spinal  Cord  and  Medulla  Oblon.sata.  B',  the  Filum 
terminals,  whirl)  has  been  cut  off  from  A  and  B.  I, 
Pyramids  of  the  medulla,  and  1'.  their  decussation. 
2  olives  ;  :i  lateral  strands  of  the  medulla  ;  4%  cala- 
mus scriptorins ;  5,  the  funiculus  gracilis;  and  6, 
the  funiculus  cuneatus  ;  7.  the  anterior,  and  9,  the 
posterior,  fissures  ;  8,  the  antero-latej-al  impression  ; 
10,  postero-lateral  groove.  C,  the  cervical,  and  L, 
the  lumbar,  enlargements  of  the  cord. 


«0- 


9- 


66 


THE   SPINAL    COED. 


median).  Both  fire  filled  to  their  bottom  with  processes  of  the  pia 
mater ;  and  the  sides  of  the  posterior  fissure  are  bound  closely  to- 
gether by  the  same  membrane. 

Each  of  these  symmetrical  and  nearly  half-cylindrical  halves  of 
the  cord  is  subdivided  by  the  lines  of  the  entrance  of  the  posterior 
and  anterior  nerve-roots  into  (2)  three  Columns  :  (a)  the  anterior, 
which  lies  between  the  anterior  median  fissui'e  and  the  anterior 
roots  ;  (6)  the  j^osterior,  which  lies  between  the  posterior  median 
fissure  and  the  posterior  roots  ;  and  (c)  the  lateral  column,  which 
lies  at  the  side  of  the  cord  between  the  other  two  columns. 

(3)  The  Commissures  of  the  spinal  cord  are  two  bands  of  ner- 
vous matter  which  unite 
its  halves,  thus  prevent- 
ing it  from  being  com- 
pletely separated  into 
two  portions  by  the 
fissures.  The  one  in 
front,  at  the  bottom  of 
the  anterior  median 
fissure,  is  composed  of 
transverse  nerve-fibres 
and  is  called  (a)  the 
anterior  white  commis- 
sure ;  the  one  behind, 
at  the  bottom  of  the 
posterior  fissure,  is  (6) 
the  posterior  gray  com- 
missure. The  gray 
commissure    is    nearly 

Fig.  14.— a,  Anterior,  and  B,  Lateral,View  of  a  Portion  of  the  twiCC     aS     large     aS     the 

Cord  from  the  Cervical  Region.  Vi-    (Schwalbe.)  1,  Anterior  ■rY|jjJ;;e        CXCCpt      at      the 

median,  and  2,  posterior  median,  fissures.     At  3  is  the  an-  '                  ^ 

terolateral  impression,  over  which  spread  the  anterior  roots  cCrvical  and  lumbar  CU- 
(5).     The  posteri(jr  roots  (6),  with  tlieir  ganglion  ((>'),  arise 

from  the  postero-lateral  groove,  and  uniting  with  the  ante-  largCmentS  of  the    COrd, 

rior  roots  form  the  compound  nerve  (7).  ,               ,  . 

where  the  white  is 
larger.'  Along  its  whole  length  the  gray  commissure  incloses  a 
circular  or  elliptical  canal  [central  canal),  whose  diameter  is  about 
one-twenty-fifth  of  an  inch  and  which  is  lined  by  ciliated  cells.  Near 
the  central  canal  lies  ai,hin  layer  of  gelatinous  substance.  The  rest 
of  the  gray  commissure  consists  for  the  most  part  of  extremely  fine 
nerve-fibres  devoid  of  medullary  sheath;  while  the  white  com- 
missure is  composed  of  meduUated  fibres.     The  thickness  of  the 


See  Henle,  Anatomie  des  Menschen.     Text,  p.  309. 


CEESCEISTT   SHAPE    OF   THE   HORlSrS. 


67 


commissures  is,  as  a  rule,  proportional  to  the  size  of  the  corre- 
sjDonding  nerve-roots  ;  their  form,  as  they  pass  into  the  lateral 
parts  of  the  cord,  varies  in  different  sections  of  its  length. 

§  8.  Transverse  sections  of  the  spinal  cord  show  us  that,  as  its 
external  appearance  v^'ould  indicate,  the  substance  of  which  it  is 
composed  is  arranged  in  two  symmetrical  halves,  almost,  but  not 
quite  separated  by  the  median  fissures.  This  substance,  like  that 
of  all  the  nervous  centres,  consists  of  both  white  and  gray  nervous 
matter.  The  former  is  external  and  composes  the  columns  of  the 
cord  ;  while  the  latter  is  internal  and  is  surrounded  by  the  white. 
The  relative  amount  of  the  two  kinds  of  nervous  matter  varies  in  the 
different  parts  of  the  cord.  At  its  beginning  from  the  filum  termi- 
nale  scarcely  any  white  matter  appears  ;  the  amount  of  such  matter, 
however,  increases  from  below  upward,  and  is  largest  in  the  cervi- 
cal part  of  the  cord.  The  amount  of  gray  matter  is  greatest  in  the 
ujDper  and  lower  enlargements  of  the  cord. 

The  gray  columns  on  either  side  of  the  cord,  together  with  the 
commissures  which  unite  them,  form  a  figure  somewhat  like  a  large 
Eoman     X,    with    diverging 
sides;  but  the  lateral  masses  — --'''^ 

of  these  crescent-shaped  bodies 
are  narrower  in  the  thoracic 
(or  dorsal)  region,  and  broader 
in  the  cervical  and  lumbar  en- 
largements. Sometimes  the 
figure  is  rather  like  that  of  a 
large  X,  or  a  pair  of  butterflies' 
wings.  The  two  limbs  of  each 
side  of  the  figure  into  which 
the  gray  columns  are  thus 
formed  are  called  (4)  Horns  ; 
(a)  the  anterior  horn  is  round- 
ed, (6)  the  2^osterior  long  and 
narrow.  The  division  into  an- 
terior, posterior,  and  lateral 
columns,  which  is  well  marked 
on  the  external  surface  of  the  spinal  cord,  is  gradually  lost  as  we 
pass  inward  toward  the  central  gray  substance.  Of  the  two  horns 
of  each  side,  the  anterior  has  the  appearance  of  "  spongy  sub- 
stance," the  posterior  of  a  kernel  of  such  substance  surrounded  by 
gelatinous  substance. 

§  9.  Careful  study  of  the  spinal  cord  with  the  higher  powers 
of  the  microscope  has  enabled  histologists  to  describe  with  further 


Fig.  1.5. — Transverse  Section  through  the  Spinal 
Cord.  AF,  antero-median,  and  PP,  postero-median 
fissures;  PC,  posterior,  LC,  lateral,  ami  AC,  anteri- 
or columns ;  AR,  anterior,  and  PR,  posterior  nerve- 
roots  :  C,  central  canal  of  cord,  with  its  column,. r 
endothelial  lining-.  The  pia  mater  is  shown  invest- 
ing the  cord,  sending  processes  into  the  anterior 
and  posterior  fissures,  as  well  as  delicate  prolonga- 
tions into  the  columns.  The  crescentic  arrange- 
ment of  the  gray  matter  is  shown  by  the  darker 
shaded  portion. 


68 


THE   SPINAL    COED. 


details  the  manner  in  which  the  nervous  elements,  both  fibrillar  and 
granular,  are  arranged  within  the  connective  substance. 

The  White  Substance  of  the  spinal  cord,  besides  connective  tis- 
sue and  lymph-  and  blood- 
vessels, is  composed  of 
nerve-fibres  of  compara- 
tively large  or  of  medium 
size.  The  essential  constit- 
uent of  these  fibres  is  the 
axis-cylinder,  the  diameter 
of  which  is  generally  one- 
third  or  one-fourth  of  their 
breadth.  When  fully  de- 
veloped, they  are  rarely  or 
never  without  a  medullary 
sheath,  but  probably  have 
no  neurilemma.  Their  di- 
ameter is  not  constant ; 
the  thickest  fibres  ( j-^'oir  ^^ 
"SirV^  °^  ^^^  inch)  are  found 
in  the  outer  portions  of  the 
anterior  columns,  where 
their  size  is  tolerably  uni- 
form. In  the  lateral  col- 
umns the  nerve-fibres  vary 
greatly  in  size,  the  finer 
ones  lying  inward  near  ths  gi'ay  matter.  In  the  posterior  columns 
they  increase  in  thickness  as  they  approach  the  posterior  gray  com- 
missure. In  the  upper  thoracic,  and  through  the  whole  of  the  cer- 
vical, region,  there  is  found  a  wedge-shaped  bundle  of  fine  fibres 
that  is  separated  off  from  the  posterior  columns  toward  the  middle 
line  of  the  cord  by  a  strong  seiDtum  ;  this  is  called  fasciculus  gracilis, 
or  "column  of  Goll." 

The  direction  of  some  of  the  nerve-fibres  in  the  white  substance 
of  the  cord  is  vertical,  of  others,  horizontal,  of  still  others,  oblique. 
The  vertical  fibres  are  most  abundant,  are  united  with  a  parallel 
arrangement  into  fascicles  of  various  sizes,  and  ascend  toward  the 
brain.  Horizontal  fibres  in  the  white  substance  of  the  spinal  cord 
are  of  two  kinds — commissural  fibres  and  fibres  of  the  roots.  The 
fibres  of  the  white  commissure  run  horizontally  along  the  median 
border  of  the  gray  matter  of  the  horns,  and  become  interwoven  with 
the  vertical  bundles  of  the  anterior  columns.  Most  of  them  pass 
from  the  substance  of  the  anterior  horn  of  one  side  across  to  the 


Fig.  16.— Section  of  Dorsal  Part  of  the  Spinal  Cord  phow- 
ing  the  Gray  Matter  of  the  Horns.  ^%.  (Henle.) 
Ca,  anterior  while,  and  Cr.  graj'  commissure ;  Co,  cen- 
tral canal ;  v,  vesicular  column  ;  s.  spongj'  substance  of 
the  posterior  horn,  surrounded  by  g.  gelatinous  sub- 
stance ;  Pr,  reticular  process ;  Ti,  intermedian  lateral 
tract. 


COURSE    OF   FIBRES    IN   THE    CORD. 


69 


finterior  column  of  the  other  side.  The  fibres  of  the  posterior  spi- 
nal roots  run  in  a  nearly  horizontal  direction  inward  ;  they  divide 
into  anastomosing' bundles  so  minute  and  so  intricately  interwoven 
with  the  vertical  fibres  of  the  posterior  column  that  their  course 
is  difficult  to  trace.  Part  of  them  (the  lateral  ones)  run  directly 
into  the  substantia  gelatinosa  of  the  posterior  horns,  and  are,  per- 
haps, continuous  with  the  axis-cylinder  processes  of  the  nerve-cells 
of  its  spongy  kernel ;  part  of  them  appear  to  enter  the  gray  sub- 
stance of  these  horns  only  after  curving  and  running  a  variable  dis- 


.'f^ocu 


co.l. 


Fig.  17 — Section  of  the  Spinal  Cord  at  the  Level  of  the  Eighth  Pair  of  Dorsal  Nerves,  ^jy 
(Schematic,  from  Schwalbe.)  s.a.,  anterior  fissure;  s.p.,  posterior  septum  (or  Assure);  c.a., 
anterior,  and  c.p.,  posterior,  commi>sures  ;  c.c,  central  canal :  co.a,  anterior  horn  ;  co.l.,  lateral 
horn ;  vo.p.,  posterior  horn  ;  n,  anterior  lateral,  and  6,  anterior  median  cells ;  r,  cells  of  the 
lateral  horn ;  d,  columns  of  Clai-ke  ;  e,  solitary  cells  of  the  posterior  horn  ;  r.a..  the  anterior^ 
and  r.p,,  the  posterior,  roots :  f,  bundle  of  fibres  of  the  posterior  horn  ;  and  /',  bundle  of  the 
posterior  column  ;  /",  iongirudinal  fibres  of  the  posterior  horn  ;  s.g.R.,  gelatinous  substance  of 
Rolando;  /.a.,  anterior, /.i.,  lateral,  and/.p.,  posterior,  columns. 

tance  upward,  or  perhaps  downward,  in  the  posterior  columns; 
The  fibres  of  the  anterior  roots  of  the  spinal  cord  traverse  its  white 
substance  obliquely  ;  some  of  them  enter  the  gray  matter  of  the 
anterior  horns  on  the  same  side,  where  they  probably  become  con- 
tinuous with  the  axis-cylinder  processes  of  its  large  ganglion-cells  ; 
others  of  them  pass  through  the  anterior  commissure  to  the  other 
side  of  the  cord  ;  still  others  pass  into  the  lateral  columns  and  the 
posterior  horns. 

The  Gray  Substance  of  the  spinal  cord,  in  addition  to  the   same 
constituents  as  those  of  the  white  substance,  has  numerous  nerve- 


70  THE   SPIJSTAL    CORD. 

cella  Its  nerve-fibres,  wliicli  foiin  the  chief  part  of  its  mass,  and 
are  generally  non-medullatecl,  differ  from  those  of  the  white  sub- 
stance in  that  they  frequently  subdivide  and  thus  become  attenu- 
ated into  extremely  minute  plexuses.  The  ganglion-cells  of  the 
spinal  cord  are  multipolar,  and  give  off  two  kinds  of  processes  ;  one 
an  unbranched  axis-cylinder  process  and  the  others  branching  pro- 
cesses, both  being  of  a  fibrillated  character  (comp.  Chap.  I.,  §§  28 
and  29).  The  iinbranched  processes  of  the  ganglion-cells  of  the 
anterior  horns  are  probably  continuous  with  the  axis-cylinders  of 
the  nerve-fibres  of  the  anterior  spinal  roots.  Of  most  of  the  simi- 
lar processes  from  cells  in  the  posterior  horns  we  cannot  yet  make 
the  same  afiirmation.  The  branching  processes  of  the  nerve-cells 
were  traced  by  Gerlach  '  until  he  thought  himself  able  to  affirm 
that  their  finest  ramifications  participate  in  those  plexuses  of  nerve- 
fibres  which  he  regards  as  an  essential  constituent  of  the  gray  sub- 
stance of  the  cord.  Henle  ^  and  others  consider  the  fate  of  these 
processes  to  be  still  unknown. 

Characteristic  groups  of  ganglion-cells  occur  at  various  places  in 
the  sections  of  the  gray  matter  of  the  spinal  cord.  In  the  anterior 
horns  of  the  cervical  and  lumbar  regions  are  three  groups  of  large 
cells  ;  one  of  these  is  on  the  side  of  the  horn  (lateral),  one  farther 
to  the  front,  one  on  its  median  border.  They  all  coalesce  in  the 
anterior  horns  of  the  thoracic  region.  In  the  anterior  horns  also 
occur  isolated  nerve-cells  of  different  sizes.  The  middle  part  of 
the  gray  lateral  halves  of  the  spinal  cord  contains,  in  parts  of  the 
cervical  and  thoracic  regions,  isolated  groups  of  cells  ;  one  impor- 
tant group  is  situated  at  the  inner  angle  of  the  base  of  the  posterior 
horn,  and  is  called  the  "columns  of  Clarke."  The  other  nerve-cells 
of  the  posterior  horns  are  small,  and  are  not  collected  into  groups, 
but  are  distributed  through  that  part  of  the  substance  of  the  horns 
which  is  also  traversed  by  the  above-mentioned  fine  plexuses  of 
nerve-fibres  (see  Fig.  17). 

§  10.  By  careful  counting,  E,  A.  Birge '  ascertained  the  number 
of  the  elements  in  the  spinal  cords  of  several  frogs.  From  his  con- 
clusions something  may  perhaps  be  gained  toward  forming  a  better 
conception  of  this  organ.  In  seven  cases  Bu-ge  found  that  the  num- 
ber of  fibres  in  the  anterior  roots  varied  from  5,984  in  the  smallest 
animal  to  11,468  in  the  largest ;  the  number  increasing  at  the  i-ate  of 
about  one  thousand  four  hundred  and  fifty  motor  fibres  to  each  added 
ounce  of  weight  (51.5  to  the  gram).     The  diameter  of  the  fibres  was 

'  See  in  Strieker's  Human  and  Comparative  Histology,  ii.,  pp.  352  fE. 

-  Anat.  des  Menschen.     Text,  pp.  810  ff. 

3  Archiv  f.  Anat,  u.  Physiol,  1882,  Pliysiolog.  Abtli.,  pp.  435-479. 


NERVE-TKACTS    IN   THE    COED.  71 

also  found  to  be  much  enlarged,  according  to  tlie  size  and  weight  of 
the  animal ;  and  the  average  diameter  widely  different  in  the  different 
nerve-roots.  For  example,  it  varied  from  3,550  fibres,  in  the  sev- 
enth pair  of  nerves,  to  14,133  in  the  tenth  pair,  for  a  cross-sec- 
tion one  twenty-fifth  of  an  inch  square.  So,  too,  were  the  so- 
called  motor-cells  of  the  anterior  gray  columns  found  to  vary  from 
4,871  to  11,517,  according  to  the  weight  of  the  animal.  It  was 
found  that  the  large  masses  of  cells  lie  in  two  principal  gToups, 
corresponding  to  the  cervical  and  lumbar  enlargements  of  the 
cord, 

§  11.  It  would  be  of  great  interest  to  our  inquiries  if  it  were 
possible  to  give  a  complete  descrii^tion  of  the  tracts  of  the  nerve- 
fibres  in  their  passage  along  the  spinal  cord  ;  but  it  is  impossible 
for  the  microscope  to  unravel  them,  and  the  evidence  of  physiology 
is  (as  we  shall  see  subsequently),  somewhat  doubtful  and  even  con- 
flicting. Of  late,  however,  certain  of  these  paths  have  been  traced 
with  considerable  certainty  by  combining  the  methods  of  embry- 
ological  and  pathological  observation.  In  the  development  of  the 
spinal  cord,  the  medullary  substance  of  the  nerve-fibres  along  cer- 
tain tracts  of  the  white  columns  is  formed  later,  so  as  to  render 
them  distinguishable  in  cross-sections.  Moreover,  when  the  nerve- 
fibres  are  separated  from  their  place  of  origin,  degeneration  of  their 
elements  takes  place.  The  place  of  the  degenerated  nervous  sub- 
stance is  taken  by  connective  tissue,  which  behaves  differently  un- 
der the  influence  of  staining  fluids.  By  following  the  course  of 
this  degeneration  toward  their  periphery,  the  paths  of  conduction 
in  the  nerves  may  be  traced.  Some  time  ago,  Tiirck '  attempted  to 
mark  out  certain  motor  tracts  in  the  brain  by  using  this  process  of 
degeneration  as  his  guide.  Our  great  authority  at  present  on  the 
paths  of  the  nerve-fibres  in  the  sjDinal  cord  and  brain,  as  ascer- 
tained chiefly  by  the  former  of  these  methods,  is  the  work  of 
Flechsig.' 

Two  tracts  in  the  antero-lateral  columns,  which  extend  along  the 
greater  part  of  the  spinal  cord  and  into  certain  parts  of  the  brain, 
are  thus  quite  certainly  made  out.  From  their  upper  connections 
they  have  been  named  the  i^yramidal  tract  (or  tracts)  and  the  direct 
lateral  cerebellar  tract.  The  former  is  directly  traceable  down  from 
the  anterior  pyramid  of  the  medulla  oblongata.  Most  of  the  fibres 
of  this  tract  cross  over  in  the  extreme  upper  part  of  the  cord,  and 
pass  down  it  in  the  back  part  of  the  lateral  column  as  a  compact 

'  Sitzgsb.  d.  Kaiserl.  Acad.,  vi.,  pp.  303  ff. 

■^  Die  Leitungsbaliuen  im  Gehirn  u.  Riickenmark  d,  Menschen.  Leipzig, 
1876. 


72 


THE   SPIISTAL   CORD. 


bvmdle.  This  crossed  (or  lateral)  /^ari  of  the  pyramidal  tract  can 
be  traced  as  far  as  the  third  or  fourth  pair  of  the  sacral  nerves. 
But  some  of  the  fibres  from  the  pyramids  of  the  medulla  do  not 
cross  in  the  upper  part  of  the  cord.  These 
form  the  uyicrossed  (or  anterior)  part  of  the 
pyramidal  tract ;  this  part  gradually  dimin- 
ishes as  it  passes  downward,  and  ceases  in 
the  dorsal  region  of  the  cord.  The  direct 
lateral  cerebellar  tract  lies  between  the  late- 
ral pyramidal  tract  and  the  outer  surface  of 
the  cord.  It  disappears  in  the  lumbar  re- 
gion. It  is  thought  that  the  rest  of  the  ante- 
rior column  of  the  cord,  besides  the  anterior 
pyramidal  tract,  may  be,  for  the  most  part, 
commissural  in  nature — that  is,  it  serves  to 
bind  together  the  two  halves  of  the  cord  on 
the  same  level,  or  somewhat  obliquely  those 
lying  slightly  below  or  slightly  above. 

In  the  posterior  white  column  a  tract  can 
be  traced  as  far  downward  as  the  middle  of 
the  dorsal  region  of  the  cord  ;  this  is  the 
one  already  referred  to  as  the  "tract  (or 
column)  of  Goll." 

§  12.  The  spinal  cord  is,  therefore,  shown 
to  be  a  mechanism  composed  by  combining 
the  nervous  elements  so  as  to  serve  the 
great  purpose  of  conducting  nerve-commo- 
tion and  acting  as  a  series  of  reflex  and  auto- 
matic centres.  In  it  we  find  tracts  of  con- 
nected nervous  elements  for  the  movement 
of  ascending  and  descending  nervous  im- 
pulses. It  is  also  a  column  or  pile  of  ner- 
vous centres,  each  one  of  which  may  have  a 
particular  value  for  particular  functions  ; 
but  which  are  also  all  bound  together,  up 
and  down,  right  and  left,  and  obliquely,  so 
as  to  act  unitedly  under  a  certain  control 
from  each  other  and  from  the  central  organs 
lying  above.  It  is  especially  strong  in  nerve- 
cells,  just  where  it  needs  to  be  so— namely,  at  the  enlargements, 
where  it  sends  off  nerves  to  the  upper  and  lower  limbs.  Its  paths 
for  the  passage  and  diffusion  of  molecular  disturbance  are  indefi- 
nitely numerous,  and  their  intricacy  extremely  great.    It  has  groups 


Fig.  18.— Sections  through  the 
Spinal  Cord  at  diflferent  ele- 
vations, to  show  the  tracts  of 
White  Substance.  /.,  eleva- 
tion of  the  sixth  cervical 
nerves.  //.,  of  the  third  ; 
///.,  of  the  sixth  ;  and  IV., 
of  the  twelfth,  dorsal  nerves; 
and  v.,  of  the  fourth  lumbar 
nerves ;  pr,  uncrossed  (or 
anterior)  pyramidal  tract ; 
pn,  crossed  (or  lateral)  p.\ra- 
midal  tract  ;  kn,  direct  late- 
ral cerebellar  tract  ;  g,  tract 
of  Goll. 


ELEMENTS    OF   THE   INTEECEAlSriAL   OEGAlSrS.  73 

of  nerve-elements,  such  as  belong  to  the  central  organs  generally, 
of  gangiion-celis  embedded  in  neuroglia  ;  it  has  special  local  mech- 
anisms within,  and  yet  connected  with  its  general  mechanism.  It 
is  adapted  to  do  a  large  amount  and  variety  of  work  through  its 
pairs  of  nerves,  without  calling  upon  the  higher  nervous  centres ;  it 
is  constructed  so  as  to  act  like  a  system  of  relays,  not  only  trans- 
mitting, but  also  modifying,  inhibiting,  enhancing,  and  distributing 
the  impulses  which  it  receives,  both  from  the  more  central  and  from 
the  peripheral  portions  of  the  cerebro-spinal  system. 

§  13.  The  same  elements  of  nerve-fibres  and  nerve-cells,  in  con- 
junction with  connective  tissue  and  neuroglia,  and  enveloped  in  the 
three  inclosing  membranes  (dura  mater,  arachnoid,  and  pia  raater) 
already  described,  are  combined  with  an  increased  variety  and  com- 
plexity of  arrangement  to  form  those  intercranial  central  organs 
with  which  the  upper  end  of  the  spinal  cord  is  continuous.  Here, 
too,  these  elements  are  gathered  into  fascicles  of  nerve-fibres 
which  converge,  or  diverge,  and  mn  their  courses  in  various  direc- 
tions, and  into  ganglionic  masses,  in  which,  besides  the  nerve-fibres, 
nerve-cells  and  diffused  finely  granular  substance  of  a  doubtful 
physiological  character  are  found.  Uniformity  of  elementary  parts, 
together  with  the  greatest  intricacy  of  arrangement,  prevails,  above 
all  other  regions  of  the  body,  in  the  structure  of  the  brain.  The 
significance  of  the  elements  and  elementary  parts  can,  therefore, 
only  be  understood  when  they  are  considered  in  the  localities  and 
relations  to  other  parts  which  are  assigned  them  by  this  so  intricate 
arrangement. 

§  14.  The  Encephalon,  or  Brain,  in  the  most  extended  sense  of 
the  word,  includes  all  that  portion  of  the  central  nervous  axis  which 
is  contained  within  the  cavity  of  the  skull.  This  grand  mass  of 
nervous  matter  may  be  divided  into  several  parts,  somewhat  differ- 
ently marked  off  according  to  the  point  of  view  from  which  the 
division  proceeds.  The  division  proposed  by  Meynert ' — to  which 
reference  will  be  made  later — is  based  upon  the  supposed  physio- 
logical significance  of  the  different  parts,  and  upon  their  arrange- 
ment so  as  to  discharge  the  functions  of  conduction  and  "  suscep- 
tibility to  impressions."  For,  as  this  authority  rightly  claims,  "  a 
purely  histological  description  "  is  of  comparatively  little  service 
in  comprehending  the  meaning  of  the  architecture  of  the  brain. 
We  shall,  first  of  all,  however,  describe  briefly  the  contents  of  the 
cranial  cavity,  as  it  appears  both  to  the  unaided  eye  and  under  the 
microscope,  without  reference  to  theory. 

'  In  Strieker,  Human  and  Comparative  Histology,  ii. ,  pp.  367  S. 


74 


STEUCTUKE   OF   THE   BEAIN. 


On  removing  tlie  entire  brain  from  the  skull,  the  following  foul 
divisions  of  its  mass  engage  the  attention  of  even  the  inexperienced 
observer.  Immediately  above  the  section  by  which  it  has  been  sepa- 
rated from  the  spinal  cord,  and  appearing  as  an  enlarged  prolonga- 
tion of  the  cord,  is  (I.)  the  Medulla  Oblongata.  Covering  the  ujojoer 
back  part  of  this  oi'gan,  and  extending  beyond  it  on  both  sides, 
with  its  surface  divided  into  small  lobes  by  furrows,  is  (II.)  the 
Cerebellum,  or  little  or  hinder  brain.  Swelling  out  in  front  of  and 
above  the  medulla  is  (m.)  the  Pons  Varolii,  or  so-called  "bridge" 
of  the  brain.  While  in  two  hemispheres  separated  by  a  deep  fis- 
sure, above  both  pons  and  cerebellum,  and  filling  the  larger  part 
of  the  cranial  cavity,  is  seen  (lY.)  the  Cerebrum,  or  large  brain,  or 


Fig.  19. — View  of  the  Brain  in  Profile,     y,.    (Henle.)     C6,  cerebrum;   C5?,  cerebellum  ;  Jfo,  me- 
dulla oblongata ;  P,  pons  Varolii, 

brain  proper.  These  divisions  are  all  readily  distinguishable  on 
the  external  surfaces  of  the  Encephalon. 

On  laying  the  encephalic  mass  open,  however,  certain  bodies  of 
nervous  matter  are  disclosed  that  have  been  concealed  beneath  the 
cerebellum  and  the  cerebrum,  and  that — although  ordinarily  re- 
garded as  parts  of  the  latter — are  scarcely  to  be  included  in  any  one 
of  the  four  main  divisions  of  the  brain.  We  shall  describe  in  order 
the  organs  just  named. 

§  15.  I.  The  Medulla  Oblongata  is  somewhat  pyramidal  in  form, 
about  one  and  one-fourth  inch  in  length,  from  three-fourths  to  one 
inch  broad  in  its  widest  part,  and  one-half  inch  thick  ;  it  extends 
from  the  spinal  aperture  of  the  cranial  cavity  {foramen  magnum)  to 
the  lower  border  of  the  pons  Varolii.  It  is  continuous  with  the 
spinal  cord,  and  somewhat  resembles  it  in  the  divisions  of  its  ex- 
ternal surface.     Its  anterior  pyramids  appear  superficially  continu- 


extekjstal  aspect  of  the  medulla. 


75 


Fva. 


ous  with  the  anterior  columns  of  the  cord  ;  its  lateral  area  shows 
upon  its  upper  end  an  oval-shaped  elevation  called  the  "  olivary 
body  ;  "  its  posterior  tracts  also  appear  continuous  with  the  poste- 
rior columns  of  the  cord.  Just  outside  the  upper  portion  of  each 
posterior  tract,  and  behind  the  olive,  ascends  to  the  cerebellum  a 
strong  tract  named 
the  "restiform  body." 
That  portion  of  the 
posterior  column  of 
the  upper  cord  (al- 
ready referred  to,  p. 
G8)  which  is  marked 
off  from  the  rest  by  a 
septum  of  pia  mater, 
is  continued  up  into 
the  medulla  oblonga- 
ta, and  becomes  more 
strongly  marked.  It 
is  known  as  the  fu- 
niculus gracilis  ;  and 
when  traced  still  far- 
ther upward  is  seen  to 
broaden  out  into  an 
expansion  called  the 
clava.  A  prolongation 
of  the  posterior  lateral 
column  also  gradually 
expands  as  it  ascends,  so  that  it  acquires  a  "  wedge-shape  "  form, 
and  is  accordingly  known  as  the  cuneate  funiculus. 

The  medulla  oblongata,  like  the  spinal  cord,  is  composed  of  white 
and  gray  nervous  matter  ;  it  differs  from  the  cord,  howevei",  in  hav- 
ing its  gray  matter  not  confined  to  the  central  part,  but  gath- 
ered more  into  special  masses  or  nuclei.  A  redistribution  of  the 
nerve-elements  takes  place  in  the  medulla,  and  their  arrangement 
becomes  more  complex.  An  important  part  of  this  redistribution 
is  accomplished  by  the  divergence  of  the  posterior  tracts  and  resti- 
form bodies,  which  opens  up  the  central  gray  mass,  and  lets  it 
come  to  the  surface  between  the  sides  of  the  surrounding  white 
matter.  Looking  at  this  redistribution  as  it  appears  from  below, 
the  elements  of  the  cord  may  be  said  to  be  spread  out  and  increased 
by  the  addition  of  new  elements  ;  looking  at  it  as  it  appears  from 
above,  the  tvro  great  nerve-tracts  of  the  cerebrum  (tegmentum  and 
crusta  of  the  crus  cerebri),  and  the  tract  of  the  cerebellum,  may  be 


Fig.  90. — Back  View  of  the  Medulla  Oblongata,  the  Cerebellum 
being  removed.  (Henle.)  Cq,  corpus  quadrigeminum  ;  Lc, 
locus  ccei-uleus  ;  F,  flocculus  of  the  cerebellum;  Ac,  ala  ci- 
nerea  ;  and  Ac'  Siilling's  nucleus  accessorius ;  01,  clava  ;  Fc, 
funiculus  cuneatus  ;  Fg,  funiculus  gracilis. 


76 


STKUCTURE   OF   THE   BRAIN. 


said  to  be  gathered  up  in  the  medulla,  and  compi-essed  so  as  to 
form  in  the  cord  a  continuous  and  symmetrical  medullary  invest- 
ment for  its  central  gray  matter. 

The  intimate  structure  of  this  organ  is  exceedingly  complicated  ; 
much  of  it  is  doubtful,  and  as  yet  impossible  to  make  out  satis- 
factorily. The  two  important  considerations  are  (1)  to  trace  the 
nerve-fibres  as  they  ascend  through  the  medulla  from  the  various 
columns  of  the  cord,  and  (2)  to  locate  the  particular  collections 
of  gray  matter,  whether  as  continuous  with  those  of  the  cord  or  as 
consisting  of  independent  masses. 

The  various  tracts  of  White  Matter  in  the  medulla  oblongata, 
although  they  supei-ficially  appear  to  be  prolongations  of  the  col- 


fr 


Fig.  21. — Section  showing  the  Decussation  of  the  Pyramids  at  the  point  ■where  the  Spinal  Cord 
passes  into  the  Meriulla  Oblongata.  "/, .  (Sohwalbe. )  f.l.a.,  longitudinal  anterior  fissure, 
through  which  the  bundles  of  pyramidal  fibres  (py,  lyy'),  are  crossing  over  at  d  ;  V,  anterior, 
and  S.  lateral  pyramids:  C.a.,  anterior  hnrn  with  srroups  of  ganglion-cells,  a  and  t> :  cc.  cen- 
tral canal;  /.»■.,  formatio  reticularis;  ce,  the  nick,  and  fir,  the  head,  of  the  posterior  horn; 
n.c,  nucleus  of  the  funiculus  cuneatus ;  and  w.fif.,  of  the  funiculus  gracilis ;  B',  funiculus  gra- 
cilis ;  JJ  ^,  funiculus  cuneatus ;  x,  group  of  ganglion  cells. 


umns  of  the  spinal  cord,  are  reall}^  so  to  a  small  extent  only.  This 
fact  is  most  clearly  made  obvious  by  a  comparison  of  successive 
transverse  sections.  A  large  bundle  of  fibres,  which  in  the  cord 
lies  in  the  posterior  part  of  the  lateral  column  (see  p.  71  f.),  pushes 
its  way  obliquely  through  the  gray  matter  of  the  anterior  horn,  and 
passes  in  front  of  the  central  canal  to  the  pyramid  of  the  opposite 
side.     The  crossing  of  this  bundle,  as  seen  in  the  anterior  median 


DECUSSATION"   OF   THE   PYKAMIDS.  77 

fissure  at  the  lowei*  part  of  the  medulla,  is  called  the  "  decussation 
of  the  pyramids."  The  abrupt  passage  of  so  many  fibres  through  it 
breaks  up  the  anterior  horn,  separates  part  of  it  from  the  rest,  and 
pushes  this  sej^arated  part  over  to  one  side,  so  that  it  comes  to  lie 
close  to  a  part  of  the  posterior  horn.  The  latter  also  becomes  gradu- 
ally shifted  sidewise  by  an  increase  in  the  size  of  the  posterior 
tracts,  so  that  it  comes  to  lie  almost  at  right  angles  to  the  posterior 
median  fissure  ;  its  head  enlarges  and  approaches  close  to  the  sur- 
face, where  it  forms  a  projection  (funiculus  of  Rolando),  and,  higher 
up,  a  distinct  swelling  {tubercle  of  Rolando).  Tracing  the  princi- 
]Dal  bundles  of  fibres  on  their  course  from  the  columns  of  the  spinal 
cord  upward  through  the  medulla  oblongata,  we  find  (in  accordance 
with  what  has  already  been  said)  that  the  posterior  column  forms  the 
substance  of  the  three  posterior  funiculi  of  the  medulla — namely, 
gracilis,  cuneatus,  and  funiculus  of  Rolando  :  a  considerable  part 
of  the  lateral  column  {tlie  lateral  pyra-niidal  tract,  see  p.  72)  passes 
into  the  opposite  pyramid  of  the  medulla,  and  ascends  in  it  toward 
the  cerebrum  in  company  with  a  small  part  of  the  anterior  column 
of  the  same  side  ;  while  another  part  of  the  lateral  column  (the 
direct  lateral  cerebellar  tract)  passes  at  about  the  middle  of  the 
medulla  obliquely  backward  to  the  restiform  body,  and  the  rest  of 
it  dips  under  the  olives,  and  is  continued  toward  the  corpora  quad- 
rigeminum  and  optic  thalamus.  Most  of  the  anterior  column  dips 
under  the  pyramid,  and  passes  upward  toward  the  cerebrum,  but 
part  is  continued  into- the  pyramid  of  the  same  side. 

Curved  fibres  may  also  be  seen  running  their  course  in  the  plane 
of  the  different  transverse  sections — some  superficial,  some  deep 
(arciform  or  arcuate  fibres). 

As  the  medulla  is  a  bilateral  organ,  its  halves  are  bound  together 
by  commissural  fibres,  which  run  obliquely  and  decussate  in  the 
mesial  plane,  forming  a  well-marked  band  called  raphe.  In  addi- 
tion to  the  fibres  of  the  medulla  oblongata  which  are  continuous 
Avith  those  of  the  spinal  cord,  others  originate  within  the  organ 
itself.  It  is  a  centre  of  origin  for  several  pairs  of  encephalic 
nerves. 

The  Gray  Matter  of  the  medulla  oblongata  is,  in  part,  continu- 
ous with  that  of  the  cord,  and  in  j)art  consists  of  independent  masses. 
The  former  part  is,  as  we  have  seen,  broken  up  and  rearranged  by 
the  decussation  of  the  j^yramids.  The  fate  of  the  posterior  horns 
and  of  the  central  gray  substance  has  already  been  described.  The 
substance  of  the  anterior  horns  becomes  divided  into  many  little 
masses  by  the  nerve-fibres  that  traverse  it,  so  as  to  form  a  coarse 
network  of  nervous  matter  (formatio  reticularis)  containing  nerve- 


rs 


STEUCTUEE   OF  THE  BEAIN". 


cells,  and  intersected  by  bundles  of  fibres.  In  the  upper  part  of 
the  organ  its  interior  gray  matter  appears  upon  the  floor  of  the 
fourth  ventricle,  into  which  the  central  canal  dilates.     Four  special 

kernels  or  nuclei,  of  gelatinous 
appearance  and  containing  few 
multipolar  nerve-cells,  are  to  be 
noted  in  each  half  of  the  me- 
dulla. These  are  (1)  the  nucle- 
us arciformis,  which  is  situated 
just  beneath  the  pia  mater,  at 
the  front  of  the  anterior  pyra- 
mid ;  (2)  the  nucleus  olivaris,  or 
dentate  body  (corpus  dentatum), 
which  is  within  the  inferior 
olive,  a  mass  of  gTay  matter 
folded  in  a  zigzag  or  denticu- 
lated manner,  forming  a  sort  of 
capsule  through  the  openings 
of  which  closely  packed  masses 

Fig.   22.— Section   showing  Gray  Matter  of  the  of  fibres  run  into  the  SUrrOUnd- 

Medulla  Oblongata,  in  the  region  of  the  upper  .  /o\    j.i  7  ?• 

crossing    of    the    Pyramids.     Vi-     (Schwalbe.)  lUg  SpaCC  ;     [6)    tlie  nUCieUS    OLl- 
f.l.a.,  anterior,   and   ft.lp.,   posterior,   fissures;  .  -  ■,■• 

n.XI.  i,nd  n.XII.,  nuclei  of  the  vagus  accessori-  WTIS  aCCeSSOTlUS,   a  Smaller  gray 

us  and  hypoglossal  nerves ;  d.a..  so  called  upper  „,„„„    Ivitio-    on     thp    nnt«?iVlp    nf 

crossing  of  the  pyramids;    py.    anterior  pyra-  mdbb    1^  ing     OH     UUe     OULblUe    OI 

mid  in  which  i- .*.«»•  the  nucleus  arciformis;  ^j^g  dentate  bodv  ;  and  (4)  the 

o,  beguniing  of  the  olivary  :iucleus:  oi,  acces-  J    ^  \    I         ^ 

sory  olivary  nucleus;  /^.r.  formatio  reticularis;    nUClcUS  pyramid  allS   (sOmetimCS 
{7,  substantia  gelatinosa; /.a., /.«.', /.a.-',  arci-  . 

form  fibres.  ^-Iso  Called  "  inner  accessory  nu- 

cleus "  of  the  olive),  lying  on  the  inside  of  the  same  body.  Another 
kind  of  collections  of  gray  matter  in  the  medulla  consists  of  those 
groups  of  multipolar  cells  to  which  the  nerves  that  have  here  their 
so-called  roots  of  origin  can  be  traced.  These  cells,  resemble  those 
of  the  gray  columns  of  the  cord — the  larger  ones  apparently  being 
connected  with  the  roots  of  the  motor  nerves,  the  smaller  with 
those  of  the  sensory.  It  may  be  assumed  that  some  of  their  pro- 
cesses are  continuous  with  the  axis-cylinders  of  the  fibres  of  the 
nerve-roots,  and  that  others  serve  to  place  the  medulla  in  direct 
connection  with  the  cerebrum  ;  positive  demonstration  of  these  as- 
sumptions, however,  requires  further  histological  researches.  The 
nerve-nuclei  in  the  medulla  receive  their  name  from  the  nerves 
whose  fibres  originate  in  them, 

§  16.  n.  In  the  Cerebellum,  or  Little  Brain,  the  general  arrange- 
ment of  the  two  kinds  of  nervous  matter  is  the  reverse  of  that  of 
the  spinal  cord  and  the  medulla  oblongata  :  the  gray  matter  is 
external,  the  white  internal.     More   precisely,  the  cerebellum  is 


PEDUNCLES   OF   THE   CEREBELLUM.  79 

a  white  or  medullary  mass  rising  out  of  three  large  bundles  or 
stalks  of  nerve-fibres  on  each  side,  and  enveloped  with  a  covering 
of  gray  nervous  matter.  Like  the  other  organs  of  the  cerebro- 
spinal system,  it  is  a  bilateral  structure.  These  stalks  of  nerves 
connect  the  cerebellum  with  three  other  organs,  with  parts  of 
which  they  are  continuous.  Considered,  as  connections,  they  are 
called  the  "  peduncles  "  or  crura  of  the  cerebellum.  Of  the  three 
peduncles,  (1)  one  {inferior  peduncle)  on  each  half  of  the  organ  is 
identical  with  the  restiform  fascicle  which  ascends  from  the  me- 
dulla to  the  cerebellum  ;  (2)  another  {superior  j^edunde),  similar  to 
the  first  in  size,  passes  forward,  over  the  anterior  end.  of  the  fourth 
ventricle,  and.  connects  the  cerebellum  with  the  tegmentum  of  the 
crus  ;  (3)  a  third  {middle  peduncle)  passes  down  on  each  side  into 
the  pons.  This  middle  peduncle  forms  the  larger  portion  of  the 
white  core  of  the  organ.  In  addition  to  the  fibres  from  these  three 
sets  of  peduncles,  this  core  is  in  part  constituted  by  others  which 
arise  in  the  cerebellum  itself ;  some  of  the  latter  connect  together 
the  different  regions  of  the  organ  lying  above  or  below  each  other, 
some  unite  the  opposite  and  symmetrical  regions  of  its  hemi- 
spheres. 

The  interior  relations  of  the  fibres  from  the  three  peduncles  are, 
on  account  of  the  extreme  intricacy  of  their  course,  not  yet  fully 
made  out.  United  in  the  white  core  of  the  cerebellum,  they  form 
a  rather  uniform  mass,  which  is  interrupted,  however,  by  certain 
nuclei  of  a  gelatinous  appearance.  Within  either  hemisphere,  and 
to  be  disclosed  by  cutting  through  it  a  little  to  the  outer  side  of  the 
median  lobe,  is  a  mass  of  nervous  matter  arranged  like  the  den- 
tate body  of  the  medvilla  oblongata  ;  it  is  the  corpus  dentatum  of 
the  cerebellum.  Other  smaller,  round,  or  oblate  masses  of  gray 
matter  are  found  toward  the  middle  of  the  core  from  the  dentate 
body. 

The  arrangement  of  the  gray  matter  which  forms  the  rind  or 
cortex  of  the  cerebellum  is  somewhat  peculiar ;  its  characteristics 
are  best  seen  by  examining  a  cross-section.  It  is  thus  found  that 
this  cortical  gray  substance  is  arranged  in  thin  plates,  or  lamellae, 
which  are  penetrated  by  prolongations  of  the  white  matter  of  the 
core  ;  these  prolongations  branch  off  into  the  interior  of  the  lamel- 
lae, and  give  to  the  coi'tex  the  arborescent  appearance  known  by 
the  name  of  "arbor  vitce."  The  primary  branches  of  this  tree-like 
prolongation  of  the  white  matter  of  the  core  within  the  gray  mat- 
ter of  the  cortex  stand  either  perpendicular  or  a  little  inclined  to 
the  surface  of  the  core.  The  smaller  branches  run  from  one  side  to 
another  transversely  or  forward  in  concave  curves. 


80 


STRUCTURE   OF   THE   BRAITST. 


The  external  surface  of  the  cerebellum  presents  two  hemispheres, 
or  lateral  lobes,  united  by  a  central  lobe  called  the  vermiform  pro- 
cess. This  central  lobe  on  its  upper  (or  tentorial)  surface  is  a  mere 
elevation,  but  the  "vermiform"  character  of  its  lower  (or  occipital) 
surface  is  well  defined.  The  process  here  lies  at  the  bottom  of  a 
deep  fossa  {vallecula).  From  the  middle  peduncle  of  each  hemi- 
sphere a  large  horizontal  fissure  extends  backward  along  its  outer 
border,  and  divides  the  hemisphere  into  its  tentorial  and  occipital 


Pig.  23 — Lower  Surface  of  Cerebellum.  %.  (After  Sappey. )  ],  in f prior  vermiform  process; 
2,  2,  vallecula  :  5,  flocculus ;  6,  pons  Varolii  ;  8,  middle  jieduncle  of  the  Cerebellum  :  9,  medulla 
oblongata.  Various  pairs  of  nerves  are  seen  thus:  12  and  13,  roots  of  fifth  pair  ;  14,  sixth 
pair;  15,  facial  nerve;  17,  auditory;  18,  glosso-pharyngeal ;  19,  pneumo-gastric ;  20,  spinal 
accessory  ;  21,  hypoglossal. 

surfaces.     Each  of  these  surfaces  is  divided  by  fissures  into  smaller 
lobes  or  lobules. 

In  the  gray  matter  of  the  cortex  of  the  cerebellum  three  distinct 
layers  of  nervous  substance  maj'  be  distinguished.  Of  these  the 
pure  gray  layer  is  the  most  external ;  it  is  sometimes  called  the 
"  molecular  layer."  It  consists  of  an  extremely  delicate  framework 
of  connective  tissue,  in  which,  together  with  nuclei  of  the  connec- 
tive tissue,  a  few  roundish  cells  and  minute  fi.bres  of  nervous  struct- 
ure appear.  The  middle  layer  is  cellular  and  composed  of  a  single 
irregular  row  of  large  ganglion-cells,  called  "  cells  or  corpuscles  of 
Purkinje."  Comparatively  large  processes  from  these  cells  branch 
into  and  ramify  within  the  outer  layer.  According  to  most  observers 
(Kolliker,  Deiters,  and  others)  each  of  the  cells  sends  a  single  me- 
dullated  and  unbranched  process  inward,  which  becomes  continu- 
ous with  the  axis-cylinder  of  a  fibre  of  the  medullary  portion  of  this 
organ  ;  but  according  to  Stilling  there  are  several  branches  from 
each,  which  divide  to  form  a  network  in  the  internal  layer.     This 


THE   PO]SrS   VAROLII. 


81 


layer  is  rust-colored  and  merges  gradually  into  the  white  substance 
of  the  core  ;  it  appears  to  contain  multitudes  of  granules,  with  a 
well-defined  nucleus  surrounded  by  branching  protoplasm.  The 
nature  of  the  granules  is  not  known  ;  they  have  been  considered 
by  some  as  elements  of  sustentacular  tissue,  by  others  as  lymph- 
corpuscles,  by  others  as  multipolar  nerve-corpuscles. 

The  cerebellum  is  thus  constituted  by  a  complex  arrangement 
of  the  nervous  elements  as  a  kind  of  side  mechanism  of  the  nervous 
system,  lying  out  of  the  course  of  its  direct  tracts  and  yet  bound 
by  nervous  cords  (the  peduncles)  in  all  directions  to  the  other 
oi'gans  of  the  brain. 

§  17.  in.  The  Pons  Varolii,  or  Bridge  of  the  Brain,  has  its  princi- 
pal office  in  the  mechanism  of  the  central  organs  of  the  cranial 
cavity  as  a  meeting-  and  switching-place  of  nerve-tracts  between 
other  organs  ;  but  it  is  also  itself  a  central  organ,  as  well  as  a  cen- 
tre of  origin  for  certain  nerve-fibres.     The  pons  is  really  a  thicken- 


ca> 


Fig.  24.— Median  Section  through  the  Stem  of  tTie  Brain.  (After  Reichert.)  M,  medulla  oblon- 
gata ;  of  whichPa  are  the  pyramid?,  decussating  atprf  ;  c,  central  canal ;  pp.  restiform  body  ; 
Pv,  pons  Varolii ;  F4,  fourth  ventricle,  au,  arbor  vitte  of  the  cerebellum  ;  p,  pyramid  ;  u, 
nvula  ;  re,  nodule  ;  as,  aqueduct  of  Sylvius  ;  CV,  crus  cerebri ;  Q,  corpora  quadrigemina  ;  P, 
pineal  gland  ;  Th,  optic  thalamus.  Commissures  :  ra.  the  anterior;  cm,  the  mollis  ;  and  cp,  the 
posterior.   F3,  the  third  ventricle ;  /I,  corpus  albicans;  Zc,  tuber  cinereum  ;  i,  infundibulum. 

ing  of  the  ventral  wall  of  the  fourth  ventricle,  composed  of  the  mid- 
dle peduncles  of  the  cerebellum  encircling  and  partly  blending  with 
the  continuation  upward  of  the  medulla  oblongata.  Its  superficial 
fibres  on  the  ventral  surface  are  transverse  in  their  general  direc- 
tion ;  but  the  middle  fibres  pass  directly  across,  the  lower  ascend 
sUghtly,  and  the  superior  are  more  curved,  and  descend  obliquely 
6 


82  STRUCTURE   OF   THE   BRAIN. 

to  reach  the  crus  cerebelli.  On  removing  these  superficial  fibres 
the  prolonged  fibres  of  the  anterior  pyramids  are  exposed  to  view. 
These,  as  they  ascend  through  the  pons,  are  intersected  by  the 
transverse  fibres.  At  the  low^er  part  of  the  organ,  behind  the  fibres 
from  the  anterior  pyramids,  a  special  set  of  transverse  fibres  (tra- 
riezium)  begins  at  a  collection  of  gray  matter  [superior  olivary 
nucleus)  on  one  side,  and  crosses  the  middle  line  to  ascend  to  the 
cerebellum  on  the  other  side. 

Nuclei  of  gray  matter  with  small  multipolar  nerve-cells  are  found 
everywhere  between  the  fibres  of  the  ventral  part  of  the  pons. 
Many  of  its  transverse  fibres  are  probably  connected  with  these 
cells.  The  posterior  portion  of  this  oi'gan  is  chiefly  constituted  by 
a  continuation  upward  of  the  formatio  reticularis,  and  of  the  gray 
matter  of  the  medulla  oblongata.  In  the  reticular  formation  two 
or  three  important  collections  of  nerve-cells  lie  embedded.  One 
of  these  is  the  "  superior  olivary  nucleus,"  which  lies  behind  the 
outer  part  of  the  trapezium  and  gives  origin  to  some  of  its  nerve- 
fibres.  Of  the  other  nuclei  in  this  region,  one  gives  origin  to  the 
seventh  or  facial  nerve,  and  others  to  portions  of  the  fifth  nerve. 

§  18.  IV.  The  Cerebrum,  or  Large  Brain,  much  exceeds  in  size  all 
the  other  contents  of  the  cranial  cavity  ;  but  it  surpasses  them  more 
especially  in  the  variety  and  complexity  of  the  arrangement  here 
given  to  the  nervous  elements  ;  while  its  significance  for  the  in- 
quiries of  Physiological  Psychology  is  altogether  unique. 

As  ordinarily  described,  this  nervous  mass  includes  a  consider- 
able number  of  organs,  which  vary  in  structure,  relations,  and 
physiological  functions.  Besides  the  hemispheres  of  the  cerebrum, 
and  the  great  ganglia  (corpora  striata  and  optic  thalami)  which  lie 
at  their  base,  custom  includes  in  this  term  certain  bodies  that  ap- 
pear connected  with  the  lower  surface  of  the  mass,  viz.,  the  corj)ora 
quadrigemina,  pineal  gland,  crura  cerebri,  etc. 

§  19.  The  Cerebrum  is  of  ovoid  shape  and  is  divided — above,  in 
front,  and  behind — into  two  hemispheres  by  a  deej)  median  longi- 
tudinal fissure.  If  these  hemispheres  are  drawn  asunder  by  open- 
ing this  fissure,  they  are  seen  to  be  connected  at  its  bottom  by 
a  broad  white  band  of  nervous  matter,  the  corjnis  callosum.  The 
outer  surface  of  each  hemisphere  is  convex  and  fitted  to  the  con- 
cave inner  side  of  the  bones  of  the  skull ;  the  inner  surface  along 
the  median  fissure  is  flat,  and  separated  from  the  corresponding- 
surface  of  the  other  hemisphere  by  a  process  of  the  dura  mater 
{falx  cerebri)  ;  its  under  surface  is  separated  from  the  cerebellum 
and  the  pons  by  another  process  of  the  same  membrane  [tentorium). 
From  the  front  of  the  pons  the  large  wliite  nervous  cords,  called 


BASAL   ASPECT   OF   THE   CEREBRUM.  83 

cerebral  peduncles,  or  crura  cerebri,  pass  upward  and  forward  to 
connect  the  cereln-um  with  the  organs  lying  below  it.  Around 
each  crus  winds  a  flat  band,  the  optic  tract ;  these  tracts  come  to- 
gether in  front  to  form  the  optic  commissiire  from  which  the  two 
optic  nerves  arise.  The  lozenge-shaped  space  enclosed  by  the 
crura  cerebri,  the  optic  tracts,  and  optic  commissure,  contains  a 


Fig.  25 Under  Aspect  of  the  Brain.  (Henle.)  B,  basis  of  the  crura  cerebri ;  Oca,  corpora  al- 
bican Ha  :  I',  olfactorv  bulb;  II'.  optic  tract;  Tc,  tuber  cinereum ;  Lpp,  posterior  perforated 
space  :  Ccl,  corpus  ca'llosum  ;  Let.  lamina  cinerea  terminalis  ;  Spa,  anterior  perforated  space  ; 
T,  tegmentum  ;  Tho.  thalamus  opticus;  P,  pons;  Mo,  medulla  oblongata;  I.  to  VIII.,  tirst  to 
eigrhth  pair  of  cranial  nerves. 

gray  layer  {posterior  perforated  space),  two  small  white  bodies  (cor- 
pora albicaniia),  and  a  gray  nodule  {tuber  cinereum)  which  is  joined 
to  a  small  reddish-gray  oval  mass  {pituitary  body)  by  a  conical  pro- 
cess of  gray  matter  {ivfundibulum).  In  front  of  the  optic  commis- 
sure is  a  thin  layer  of  gray  substance  (lamina  cinerea) ;  and  on  each 
side  of  the  deep  longitudinal  fissure  stretches  the  olfactory  tract, 


84 


STRUCTURE   OF   THE   BRAllSr. 


with  its  bulb.  The  intercranial  j)art  of  this  "nerve  "  is  now  known 
really  to  be  a  projecting  portion  of  the  brain.  All  these  structures, 
together  with  the  cut  ends  of  the  several  pairs  of  cranial  nerves, 
may  be  seen  upon  the  under  surface  of  the  cerebrum. 

§  20.  The  upper  surface  of  the  cerebral  hemispheres  presents  the 
appearance  of  gray  nervous  matter  arranged  in  folds  which  are 
called  "  convolutions  "  or  gyri.  These  convolutions  are  separated  by 
"fissures  "  or  sulci  of  varying  depth,  some  of  which  are  so  constant 
and  strongly  marked  that  their  presence  is  employed  to  divide  the 
surface  of  the  hemispheres  into  lobes,  while  others,  less  strongly 
marked,  separate  from  each  other  the  convolutions  of  the  same 
lobe.  It  is  the  arrangement  of  the  convolutions,  with  their  sep- 
arating fissures,  which  gives  the  hemispheres  of  the  brain  their 
characteristic  appearance,  and  which  fits  them  for  their  unique 
functions  in  the  economy  of  the  nervous  mechanism. 


FlQ.  26.— To  show  the  Right  Ventricle  and  the  Left  Half  of  the  Corpus  Callosum.  a,  transverse 
fibres,  and  &,  longitudinal  fibres  of  corpus  callosum  ;  c,  anterior,  and  d,  posterior  cornua  of  lat- 
eral ventricle  ;  e,  septum  lucidum  ;  /,  corpus  striatum  ;  (),  ttenia  semicircularis ;  h,  optic  thala- 
mus ;  k,  choroid  plexus  ;  I,  teenia  hippocampi ;  ni,  hippocampus  major ;  n,  hippocampus 
minor ;  o,  eminentia  coUateraLis. 

§  21,  By  cutting  off  successive  slices  from  the  upper  part  of  the 
hemispheres  their  general  internal  structure  may  be  seen.     It  re- 


YENTRTCLES    OF   THE   CEREBRUM. 


85 


sembles  the  plan  upon  which  the  cerebellum  is  constructed.     A 
core  of  white  nervous  matter  is  surrounded  by  a  shell  or  cortex  of 
gray  ;  the  two  lateral  halves  of  the  core  are  bound  together  by  a 
strong  band  of  fibres, 
usually  described  as 
commissural  {corpus 
callosum),    which    is 
itself  overlapped  by 
one     of     the     most 
marked  convolutions 
of   the   brain  {gyrus 
fornicatus).     By  cut- 
ting still  deeper  it  is 
found  that  the  cor- 
pus callosum   forms 
the  roof  of  a  space  in 
the  interior  of  each 
hemisphere  [the  late- 
ral ventricles).  These 
two  cavities  or  ven- 
tricles are  moistened 
by  a  serous  fluid  and 
separated  by  a  thin 
transparent  wall  {sep- 
tum  lucidum).     The 
roof  of  another  cav- 
ity, the  third  ventri-  fo 
cle,  is  formed  by  an   *-  -■ 
expanded  fold  of  the 
pia  mater  {velum  in- 
terpodtum),  the  mar- 
gins   of    which    are 
fringed   by   the    so- 
called  "choroid  plex- 
uses ; "      the     latter 
contain    the   minute 
arteries   which   sup- 
ply the  nervous  structures  of  this  region.     Each  lateral  ventricle  is 
divided  into  a  central  space  and  three  curved  prolongations  or  coi'- 
nica  ;  of  the  cornua,  one  (the  anterior)  extends  forward  and  outward 
toward  the  fi"ont  part  of  the  cerebrum  ;  one  (the  posterior^)  curves 
backward,  outward,  and  then  inward ;  and  the  third  (the  descending) 
curves  backward,  outward,  downward,  and  then  forward  and  inward. 


Fia.  27. — Basal  Ganglia  of  the  Cerebrum  seen  from  above.  (Henle.) 
Col,  genu  of  the  corpus  callosum  ;  Cs,  corpus  striatum  ;  Vsl, 
ventricle  of  the  septum  lucidum  ;  Of,  column  of  the  fornix  ;  St, 
stria  terminalis  :  Tho,  optic  thalamus  ;  and  Ts.  its  anterior  tu- 
bercle ;  Com,  middle  coiimiissure  between  the  thalami  and  over 
the  third  ventricle ;  Pv,  pulviiiar ;  On,  conarium  or  pineal 
gland  ;  Cop,  corpus  quadrigeminum. 


STRUCTUKE   OF   THE   BEAIN. 


On  the  floor  of  each  lateral  ventricle  the  exposed  portions  of  the 
great  basal  ganglia  of  the  cerebrum  are  visible.  A  large  pear-shaped 
body  of  gray  color  is  here  seen  with  its  broad  extremity  directed 
forward  into  the  anterior  cornu  of  the  ventricle  and  its  narrow 
end  outward  and  backward.'     This  body,  on  account  of  the  striped 


Fig.  28. — A  Deeper  DisEection  of  the  Lateral  Ventricle,  and  of  the  Velum  Interpositura.  a,  un- 
der surface  of  corpus  callosum,  turned  back  ;  6,  ft,  posterior  pillars  of  the  fornix,  turned  back  ; 
c,  c,  anterior  pillars  of  the  fornix  ;  d,  velum  interpositum  and  veins  of  Galen  ;  e,  fifth  ventricle  ; 
f.  f,  corpus  striatum  ;  (/,  (j,  taenia  semicircularis ;  h.  h,  optic  thalamus ;  A',  choroid  plexus  ;  /, 
taenia  hippocampi ;  m,  hippocampus  major  in  descending  cornu;  n,  hippocampus  minor ;  o, 
eminentia  collateralis. 

appearance  which  it  presents  when  cut  open,  is  called  a  "  striate 
body"  (corpus  striatum).  It  consists  of  two  masses,  the  upper  one 
of  which  (nucleus  caudatus)  projects  into  the  lateral  ventricle  ;  the 
lower  one  is  embedded  in  the  white  substance  of  the  hemisphere  and 
forms  the  principal  part  of  the  body  (nucleus  lenticiilaris).  The  two 
are  separated  by  a  layer  of  white  matter  called  the  "  internal  capsule.'' 
Between  the  diverging  portions  of  the  striate  bodies  are  the  obloug 

'  Dalton  (Topographical  Anatomy  of  the  Brain,  Philadelphia,  1885,  ii. ,  p. 
76)  and  others  speak  as  though  the  caudate  nucleus  alone  were  to  be  called 
corpus  striatum,  the  nucleus  leuticularis  by  this  name  ;  and  the  twococsidered 
as  separate  bodies. 


THE  CRUSTA  AND  THE  TEGMENTUM.         87 

oi'  somewhat  ovoid  masses  of  the  "  optic  thalami."  Each  thalamus 
rests  upon  and  partially  embraces  one  of  the  crura  cerebri  ;  its  me- 
dian surface  forms  the  side  wall  of  the  third  ventricle,  and  upon  its 
outer  and  back  part  are  two  small  elevations,  one  on  each  side  of 
the  optic  tract  {corpora  geniculata,  internum  and  externum).  In  the 
depression  between  each  striate  body  and  the  optic  thalamus  is  a 
narrow,  whitish,  semitransparent  band  of  medullary  substance 
{f.amia  semicircular  is).  Along  the  entire  length  of  the  floor  of  the 
descending  cornu  of  the  ventricle  is  a  white  eminence  {jivppocampus 
major  or  cornu  Ammonis)  which  is  the  iuuer  surface  of  the  gyrus 
fornicatus  doubled  upon  itself  like  a  horn.  An  arch-shaped  band 
of  nerve-fibres,  consisting  of  two  lateral  halves,  which,  in  front, 
form  two  pillars  that  descend  to  the  base  of  the  cerebrum  and  be- 
come the  corpora  alhicantia,  and  which  diverge  behind  into  two  pil- 
lars that  descend  with  the  descending  cornu  of  the  ventricle  and 
connect  with  a  convolution  of  the  brain  (gyrus  hippocampi),  is  situ- 
ated beneath  the  corjDus  callosum  ;  it  is  called  the  fornix.  Behind 
and  between  the  optic  thalami,  and  resting  on  the  back  surface  of 
the  crura  cerebri,  are  four  rounded  eminences  in  two  pairs,  called 
corpora  quadrlgemina ;  the  front  pair  are  the  nates,  the  back  pair, 
testes. 

§  22.  Without  mentioning  other  more  minute  subdivisions,  super- 
ficial or  internal,  in  the  structure  of  the  cerebrum  as  seen  by  the 
unaided  eye,  we  now  consider  the  arrange-                      2_ 
ment  of  the  nerve-fibres  and  nerve-cells  in               /'''^^~^^\ 
the  more  important  organs  already  named.  y^ ■^-      \. 

Of  the  fascicles  of  nerve-fibres  belonging     s^j       t     \  \ 

to  the  cerebrum,  some  connect  it  with  the     /^>v  ;       ^/^  \ 

lower  organs  of  the  encephalon  ;  some  con-  (  -p  ^s^A^x^-"'-  J 
nect  together  its  hemispheres  ;  some  join  X^  ^ /o\^  ^^ 
different  structures  in  the  same  hemisphere  ;    fig-  29.— section  through  the 

.  Mid-brain.    (Schwalhe. )     aq  , 

some  are  roots  of  origin  for  certain  nerves.       aqueduct  of  syivius;  .«.?*.,  sub- 

_-.  ^,  PIT  1      •       J.1  stantia  nigra :  p.  crusta  of  the 

The   fibres  of  the  crura  cerebri — those       cms  cerebri ;«,  tegmentum  of 

,  T  1  J!    ii         1        •       XT      i  T  the  crus  cerebri. 

strong  peduncles  oi  the  brain  that  ascend 

from  the  pons  to  the  optic  thalami  and  the  striate  bodies — are 
arranged  in  two  groups  (criista  and  tegmentum)  separated  by  the 
gray  matter  of  the  substantia  nigra.  An  important  part  of  the 
fibres  of  the  crusta,  or  front  part  (pes)  of  the  crus,  is  continuous 
with  the  longitudinal  fibres  of  the  pons  which  come  from  the 
pyramids  of  the  medulla  ;  it  receives  some  fibres  from  the  gray  mat- 
ter of  the  substantia  nigra.  Many  of  the  fibres  of  the  crusta  ter- 
minate in  the  nuclei  of  the  striate  bodies  ;  but  some  radiate  upward 
through  the  internal  capsule   directly   to  the  gray  cortex  of  the 


88  STRUCTUEE   OF   THE   BEAH^T. 

cerebrum.  (Comp.  Fig.  24.)  Some  of  the  more  diffused  fibres  of 
the  tegmentum,  or  back  and  deeper  part  of  the  crus,  are  probably 
continued  from  the  anterior  column  of  the  cord,  and  may  be  traced 
above  to  the  optic  thalami.  Others  of  its  fibres  are  collected  into 
more  well-defined  tracts  ;  one  of  the  most  important  of  which 
comes  from  the  superior  peduncle  of  the  cerebellum,  and  has  al- 
ready been  traced  as  it  passes  forward  over  the  anterior  end  of  the 
fourth  ventricle  (see  p.  79).  The  formatio  reticularis  is  continued 
into  the  tegmentum ;  the  latter,  therefore,  has  a  considerable 
amount  of  gray  matter  containing  nerve-cells.  Some  of  its  fibres 
arise  in  these  cells.  The  superior  peduncle  of  the  cerebellum  as- 
scends,  crosses  over  to  the  other  side  beneath  the  Sylvian  aque- 
duct, and  terminates  in  a  collection  of  large  pigmented  cells  (the 
nucleus  of  the  tegmentum  or  red  nudeua). 

The  intimate  structure  of  the  striate  bodies  is  not  as  yet  entirely 
made  out.  On  its  deeper  side,  which  is  turned  toward  the  internal 
capsule,  the  nucleus  caudatus  receives  from  the  capsule  several 
bundles  of  fibres.  According  to  Meynert,  some  of  these  bundles 
serve  to  connect  this  nucleus  downward  with  the  peduncle  of  the 
cerebrum,  some  upward  with  its  cortex ;  but,  according  to  Wer- 
nicke, it  is  doubtful  if  any  of  them  pass  to  the  white  matter  of  the 
hemispheres,  or  come  directly  (that  is,  without  traversing  the  len- 
ticular nucleus)  from  the  crusta.  All  parts  of  the  nucleus  lenticu- 
laris  are  pervaded  with  white  fibres.  Some  pass  into  its  inner  zone 
from  the  adjacent  part  of  the  internal  capsule  ;  some  connect  it  with 
the  caudate  nucleus  ;  some  pass  from  it  into  the  corona  radiata, 
and  then  to  the  cerebral  cortex.  These  nuclei  appear  to  have  a 
special  connection  with  the  frontal  and  parietal  lobes,  but  also  with 
some  convolutions  of  the  temporal  lobe  and  the  island  of  Keil.  The 
gray  matter  of  this  organ  is  composed  of  delicate  connective  tissue, 
with  "free  nuclei  siDaringiy  distributed  through  it."  The  nerve- 
cells  of  the  nucleus  caudatus  are  multipolar  and  of  two  sizes  ;  some 
are  about  -g-J-y  inch  in  diameter  with  many  processes,  but  most  are 
much  smaller  (y^'o-g-  inch).  Between  the  fibres  of  the  gray  matter 
of  the  nucleus  lenticularis  are  many  cells  with  yellow  pigment  in 
them. 

The  three  collections  of  gray  matter — the  locus  niger,  and  the  cau- 
date and  lenticular  nuclei  of  the  striate  body — with  the  nerve-fibres 
which  originate  in  them  and  bind  them  together,  have  been  held  to 
constitute  a  connected  chain  of  nervous  organs,  to  which  the  name 
"ganglia  of  the  crusta"  has  been  given  by  Meynert.  Eecently, 
however,  this  relation  of  the  corpora  striata  as  "basal  gangHa,"  or 
"middle-men  "between  the  spinal  cord  and  the  cerebral  cortex,  has 


COEPUS   GENICULATUM   AND   OPTIC   THALAMUS. 


89 


been  called  in  question  by  Wernicke  and  A.  Hill.  The  latter  argues, ' 
chiefly  on  morphological  grounds,  that  the  nucleus  caudatus  should 
be  separated  from  the  optic  thalamus,  and  connected  immediately 
with  the  cortex.  This  connection,  he  thinks,  is  favored  by  the  na- 
ture of  its  development,  by  its  minute  structure,  which  differs  from 
that  of  the  thalamus,  and  by  its  resemblance  to  another  nucleus 
(the  amygdaloid)  which  has  an  undoubted  origin  from  the  cortex. 
23.  Another  chain  of  nervous  organs,  leading  between  the  pons 

Yarohi  and  the  hemispheres  of  the 
brain,  consists  of  the  tegmentum  of 
the  crus  and  its  ganglia— the  red 
nucleus  (already  described),  corpus 
subthalamicon,  the  corpora  genicu- 
lata,  and  the  optic  thalami. 

The  arrangement  of  the  nervous 
elements    in    the   external  corpus 


Corpus 
taUoswii 


Sept. 
peUuctd 


Binttrer 

Iheil  des 
Nucleus 


Cornn 
posteriua 


Fig 


Fig.  31. 


These  and  the  following  two  FiRures  show  the  arrangement  of  the  white  and  gray  substance  in 
the  interior  of  the  cerebrum.     (All  four  are  from  Gegenbaur.) 

Fig  30  —Horizontal  Section  through  the  Right  Hemisphere.  _ 
Fig  31.-Frontal  Section  through  the  Cerebrum  in  front  of  the  Fornix.     Posterior  surface  of  the 

section  displayed. 

geniculatum  is  peculiar  :  it  consists  of  alternate  layers  of  white  and 
gray  matter,  as  though  occasioned  by  laying  a  lamina  of  the  gray 
between  two  medullary  lamina?,  and  then  folding  them  in  a  zigzag 
manner.  The  nerve-cells  of  this  organ  are  from  ^-J-g-  to  gfo-  of  an 
inch  in  length,  and  ^ gVo  »*  an  inch  in  breadth ;  they  are  coarsely 
granular  and  pigmented. 

The  ojMc  thalamus  is  a  mass  of  gray  matter,  with  multipolar  and 
fusiform  cells,  traversed  by  nerve-fibres.  This  gray  matter  is  par- 
tially subdivided  into  two  parts,  an  inner  and  an  outer  nucleus. 

1  The  Plan  of  tlie  Central  Nervous  System,  pp.  35  fE. 


90 


STRUCTURE   OF   THE  BRAIIf, 


Its  free  surface  (inner  and  upper)  is  covered  by  a  layer  of  white 
fibres.  On  its  outer  surface  is  the  white  matter  of  the  internal 
capsule,  formed  by  fibres  diverging  from  the  crusta  into  the  hemi- 
spheres. All  along  this  surface  fibres  radiate  from  the  interior  of 
this  organ,  and  mingle  with  those  of  the  internal  capsule  on  their 
way  to  the  cerebral  hemispheres.  Those  in  front  pass  to  the  frontal 
lobe ;  those  in  the  middle  pass  to  the  back  part  of  the  same  lobe 
and  to  the  parietal  lobe  ;  those  behind  to  the  temporo-sphenoidal 
and  occipital  lobes. 

"The  external  and  under  surfaces  of  the  thalamus  are  not  free, 
but  are  united  with  the  other  parts  of  the  brain.  The  under  sur- 
face is  united  with  the  tegmental  j^art  of  the  crus  cerebri,  while 
the  external  surface  is  covered  by  white  substance,  that  is  formed 


Fig.  32. 


FiQ.  S3. 
Fig.  32.— Frontal  Section  through  the  Right  Hemisphere  of  the  Cerebrum  in  front  of  the  Com- 

missura  Mollis.     Posterior  surface  of  section  displayed. 
Fig.  33.— Frontal  Section  through  the  Cerebrum  back  of  the  Commissura  Mollis.     Front  surface 

of  section  displayed. 

of  fibres  of  the  crusta,  which  here  diverge  into  the  substance  of  the 
hemisphere  and  pass  between  the  thalamus  and  the  lenticular  nu- 
cleus, forming  the  so-called  'internal  cajDsule""  (comp.  p.  87  f.). 
The  cells  of  its  substance  average  about  yiy-  inch  in  length  and 
^jj-g  in  breadth ;  their  long  axis  is  parallel  to  the  course  of  the 
nerve-fascicles.  According  to  a  recent  authority,"  the  thalamus 
is  the  primary  centre  of  the  optic  nerve,  and  is  also  connected  with 
the  olfactory  nerve — originally  by  way  of  the  fornix. 

The  nervous  substance  of  the  corpora  quadrigemina  consists 
mainly  of  gray  matter  covered  externally  with  a  thin  layer  of 
nerve-fibres.     In  the  interior  of  the  upper  or  front  pair  the  most 

'  Quain's  Anatomy,  ninth  edition,  ii..  p.  324. 

^  A.  Hill,  The  Plan  of  the  Central  Kervous  System,  pp.  20  ff. 


FIBRES   OF   THE   COIlOiS^A   EADIATA.  91 

characteristic  portion  of  this  organ  is  found;  it  is  a  layer  of  fine 
nerve-fibres  running  longitudinally,  between  which  are  small,  scat- 
tered nei've-cells.  In  the  external  strata  of  these  bodies  multipolar 
cells  are  abundant ;  in  their  interior,  at  the  sides  of  the  Sylvian 
aqueduct,  is  a  collection  of  gray  matter  which  forms  a  continuation 
of  the  lining  of  the  third  ventricle.  The  nerve-cells  in  the  corpora 
quadrigemina  vary  greatly  in  size.  Most  of  those  in  the  superficial 
strata  are  small ;  but  in  the  deeper  strata  some  of  them  reach  the 
maximum  of  nearly  g^^g-  of  an  inch.  The  centres  of  origin  for  the 
third  and  fourth  nerves  are  in  that  nervous  structure  of  fine  fibrils 
and  fusiform  cells  which  lies  along  the  Sylvian  aqueduct. 

§  24.  The  arrangement  of  the  nervous  elements  in  all  the  basal 
ganglia,  as  connected  with  the  cerebral  peduncles,  indicates  the  na- 
ture of  the  mechanism  of  this  region  of  the  brain.  It  is  constructed 
so  as  to  co-ordinate  all  the  nerve-tracts  of  motion  with  those  of 
sense,  and  thus  give  to  these  ganglia  important  reflex  and  auto- 
matic powers  over  the  sensory-motor  apparatus,  while  subordinating 
them  to  the  control  of  the  nervous  centres  of  the  cerebral  cortex 
that  lie  farther  above. 

To  the  highest  and  dominating  nervous  centres  in  the  cerebral 
hemispheres  the  paths  of  nervous  impulse  are  laid  from  the  basal 
ganglia  by  that  blossoming  out,  as  it  were,  of  the  nerve-fibres  on 
their  way  to  the  white  core  of  the  cerebrum,  which  is  called  the 
"  corona  radiata."  The  corona  is  formed  by  the  fibres  that  radiate 
from  the  striate  bodies,  from  the  optic  thalami,  and  the  internal 
capsule,  into  the  convolutions  of  the  lobes  of  the  hemispheres. 

§  25.  The  combination  of  the  nervous  elements  into  the  pre- 
eminently complex  mechanism  of  the  convolutions  of  the  human 
cerebrum  may  be  described  from  two  points  of  view  ;  the  first  is 
that  from  which  their  various  external  surfaces  may  be  regarded  by 
the  unaided  eye,  the  second  that  which  histology  assumes  when  it 
examines  under  the  microscope  various  sections  made  from  layers 
of  their  substance. 

The  details  of  the  external  aspect  of  the  convolutions  vary  so  much 
in  each  individual,  and  even  in  the  two  hemispheres  of  the  same  brain, 
that  the  only  chance  of  bringing  order  out  of  this  apparent  confusion 
is  to  discover  what  is  genei'al,  and  for  the  most  part  constant,  in  the 
midst  of  what  is  particular  and  subject  to  change.  In  making  such 
discovery  the  study  of  embryology  is  especially  important.  Certain 
sulci  and  their  corresponding  gyri  appear  with  a  marked  regular- 
ity in  the  earlier  and  more  fundamental  stages  of  the  development 
of  the  foetal  brain.  So,  too,  does  the  examination  of  the  surfaces 
of  the  hemispheres  of  the  adult  brain  show  certain  degi'ees  of 


92  THE   CEREBRAL   CORTEX. 

strength  with  which  the  sulci  and  gyri  are  distinguishable,  and 
thus  enable  the  investigator  to  divide  them  into  so-called  pri- 
mary, secondary,  and  even  tertiary  classes.  Bischoff,  Ecker,  and 
others  have  aptly  compared  the  primary  gyri  to  the  large  mountain 
ranges  whose  sinuosities  give  to  an  entire  region  its  characteristic 
features  ;  the  secondary  gyri  are  like  those  subordinate  ranges 
which  are  brought  into  existence  through  the  formation  of  longi- 
tudinal valleys  (secondai-y  sulci)  in  the  main  ranges ;  while  the  ter- 
tiary convolutions  may  be  compared  to  the  small  sj)urs  which  run 
out  into  the  valleys  between  the  principal  ranges  and  from  their 
sides.  Only  the  primary  gyri  are,  as  a  rule,  pretty  regularly  dis- 
posed. 

It  is  by  means  of  the  primary  sulci  that  the  surfaces  of  the  hem- 
ispheres of  the  brain  have  been  divided  by  modern  anatomy  into 
five  territories  or  Lobes. '  The  frontier  lines  of  these  lobes,  how- 
ever, are  clearly  laid  down  only  on  some  of  the  surfaces,  while  on 
other  surfaces  the  lobes  encroach  on  each  other  without  distinct 
boundaries.  The  five  lobes  are  called  Frontal,  Parietal,  Temporo- 
sphenoidal  (also  Temporal  or  Sphenoidal),  Occipital,  and  Central, 
or  Insula,  or  Island  of  Reil ;  the  latter  does  not  stand  in  immediate 
relation  with  the  walls  of  the  skull.  The  Frontal  Lobe  is  divided 
from  the  parietal  on  its  upper  and  lateral  surface  by  the  Fissure  of 
Bolando  (sulcus  centralis)  ;  and  on  its  lower  surface  from  the  tem- 
poral lobe  by  the  horizontal  branch  of  the  Fissure  of  Sylvius.  The 
Parietal  Lobe  is  divided  from  the  temporal  for  the  greater  part 
by  the  Fissure  of  Sylvius,  and  from  the  occipital — on  its  median 
surface  completely,  but  on  its  upper  surface  only  very  incompletely 
— by  the  parieto-occipital  fissure.  The  Temporo-sphenoidal  lobe 
is  distinctly  marked  off  from  the  frontal  and  parietal,  as  already 
described  ;  while  the  boundary  line  between  it  and  the  occij)ital 
lobe  is  ill  defined.  The  Island  of  Reil  lies  concealed  between  the 
frontal,  parietal,  and  temporo-sphenoidal  lobes;  its  surface,  when 
exposed  by  drawing  aside  the  margin  of  the  Sylvian  Fissure,  shows 
a  few  short  convolutions  which  radiate  forward,  upward,  and  back- 
ward from  a  central  sj^ot  on  the  lower  surface.  The  occipital,  tem- 
poro-sphenoidal, and  frontal  lobes,  all  have  three  principal  convolu- 
tions arranged  in  parallel  tiers  (superior,  middle,  and  inferior) ;  in 
the  frontal  lobes  these  three  spring  from  the  anterior  part  of  the 
ascending  convolution  just  in  front  of  the  Fissure  of  Rolando  (that 
is,  from  the  gyrus  centralis  anterior)  and  run  forward  to  the  front 
end  of  the  cerebrum. 

'  The  convolutions  are  here  described  in  dependence  upon  the  work  o.t 
Ecker,  The  Convolutions  of  the  Human  Brain.     London,  1873. 


ARRANGEMENT   OF   THE    SULCI   AND   GYRI. 


93 


§  26.  A  few  of  the  most  important  of  the  sulci  and  gyri  need 
separate  mention  ;  the  accompanying  diagrams  will   make   clear 


Fig.  34. 


Fig.  35. 

Figs.  34  and  35.— Profile  and  Vertex  Views  of  Cerebrum.  Fr,  the  frontal  lobe  ;  Par,  parietal; 
Of,  occipital ;  Ts,  temporo-sphenoidal  lobe  ;  SS,  Sylviiin  fissure  ;  RE,  fissure  of  Rolando  ;  PO, 
parieto-occipital  fissure  ;  IP,  iiitra-parietal  fissure  ;  PP,  Parallel  fissure :  SF  and  IF,  supero- 
and  infero-froutal  fissures  ;  1,  1,  1,  inferior,  2,  2,  3.  middle,  and  3,  3,  3,  superior  frontal  convo- 
lutions ;  4,  4,  ascending  frontal  convolution  :  5,  5,  5,  ascending  parietal,  5',  postero-parietal, 
and  6,  fi.  angular  convolutions ;  A,  supra-marginal,  or  convolution  of  the  parietal  eminence  ;  7, 
7,  superior,  8,  8,  8,  middle,  and  9,  9,  9,  inferior  temporo-sphenoidal  convolutions;  10,  i-uperioi, 
11,  middle,  and  12,  inferior  occipital  convolutions  ;  a,  |3,  7,  5,  four  annectent  convolutions. 

further  details  (see  Figs,  34,  35,  and  36).     Among  the  sulci  which 
bound  the  main  territories  of  the  cerebral  hemispheres  the  Fissure 


94  THE   CEKEBEAL   CORTEX. 

of  Sylvius  is  much  the  most  important.  "It  can,"  says  Ecker, 
"  in  nowise  be  considered  in  the  same  category  as  the  rest  of  the 
sulci  on  the  surface  of  the  brain."  The  other  sulci  may  be  re- 
garded as  mere  folds  of  the  cerebral  cortex  ;  the  Fissure  of  Sylvius, 
on  the  contrary,  is  made  by  folding  the  entire  hemisphere  into  an 
arch,  with  its  concave  surface  downward,  about  the  point  of  en- 
trance of  the  crus  cerebii.  This  fissure  exists  in  the  foetal  brain  at 
the  third  month.  "  It  arises,"  say  Foster  and  Balfour,'  "  at  the  time 
when  the  hemispheres,  owing  to  their  growth  in  front  of  and  be- 
hind the  corpora  striata,  have  assumed  somewhat  the  form  of  a 
bean."  The  Fissure  of  Rolando  is  also  always  present  in  the  human 
brain.  It  makes  its  appearance  in  the  foetus  as  early  as  the  end  of 
the  fifth  month.  It  is  rarely,  if  ever,  bridged  over  by  a  secondary 
gyrus  ;  it,  therefore,  forms  a  point  of  departure  in  the  examination 
of  all  the  convolutions.     It  is  botmded  for  its  entire  length  by  two 


Pig.  36. — Convolutions  of  the  Inner  and  Tentorial  Snrfaoes  of  the  Left  Hemisphere,  i.  i,  i,  cal- 
loso-marginal  fissure,  /,  I,  calcarine  fissure;  m,m,  hippocampal  fissure;  n,  n,  collateral  fis- 
sure; PO,  parieco-oocipiUI  fissure  ;  17,  17,  marginal  convolution  ;  18, 18,  gyms  fornicatus;  18', 
quadrilateral  lobule  ;  19,  hippocampal  gyrus  ;  19',  its  recurved  end  ;  25,  occipital  lobule  ;  9,  9, 
inferior  teraporo-sphenoidal  convolution. 

important  convolutions  (the  anterior  and  posterior  central  or  as- 
cending frontal  and  ascending  parietal),  which  at  both  of  its  ends 
connect  together  in  the  form  of  an  arch.  The  fissure  which  sepa- 
rates the  parietal  from  the  occipital  lobe  [parieto -occipital)  and  the 
one  which  runs  from  before  backward  through  the  parietal  lobe 
(intra-parietal)  are  also  to  be  mentioned  among  the  more  important. 
The  intraparietal  fissure,  on  the  convexity  of  the  parietal  lobe,  in- 
cludes, between  it  and  the  median  line,  the  upper  parietal  convolu- 
tion, and  embraces  in  its  downward  and  outward  bend  the  angular 
convolution.  The  latter  convolution,  and  the  marginal  convolution 
form  the  inferior  parietal  lobule. 

>  Elements  of  Embryology,  p.  384.     London,  18S3, 


THE   FIVE   LAMINA   OF   THE   CORTEX.  95 

Besides  the  superior,  middle,  and  inferior  convolutions  of  the 
frontal,  temporo-sphenoidal,  and  occipital  lobes,  and  the  two  cen- 
tral convolutions  on  each  side  of  the  Fissure  of  Rolando,  the  follow- 
ing, which  belong  to  the  median  aspect  of  the  hemispheres,  ai'e 
to  be  noted  in  particular.  The  convolution  which  arches  around 
the  corpus  callosum,  and  is  separated  from  the  median  aspect 
of  the  first  frontal  convolution  by  a  deep  and  constant  fissure 
(the  sulcus  calloso-marginalis)  is  called  from  its  shape,  gyrus  forni- 
catus.  The  back  end  of  this  convolution  curves  downward  and  then 
forward,  under  the  name  of  gyrus  hippocampi,  to  the  inner  tip  of 
the  temporal  lobe.  The  passage  of  the  former  convolution,  without 
break,  into  the  latter,  Ecker  considers  one  of  the  most  important 
differences  between  the  hemispheres  of  the  brain  of  man  and  those 
of  the  ape. 

§  27.  Although  the  general  arrangement  of  gray  nervous  matter 
upon  the  surface,  and  of  white  matter  within,  is  adhered  to  in  all 
parts  of  the  cerebral  cortex,  the  form  and  disposition  of  the  cells 
in  the  gray  matter  differ  in  different  regions,  and  also  in  different 
layers  of  the  same  regions.  But  its  most  common  form,  which  is 
that  seen  in  the  convolutions  of  the  parietal  lobe,  corresponds  to 
what  Meynert '  has  called  "  the  general  or  five-laminated  type  of 
the  cortex  of  the  cerebrum."  There  are,  as  a  rule,  that  is  to  say, 
five  layers  or  laminae  to  be  discovered  in  the  gray  matter  of  the 
cerebral  cortex.  The  thickness  of  the  entire  cortex,  thus  com- 
posed, is,  in  the  adult,  from  -^^  to  \  of  an  inch.  The  first  of 
the  layers  consists  of  a  matrix,  in  which  delicate  nerve- fibrils  run 
parallel  to  the  surface  and  interlace  with  a  few  small  globular  or 
elongated  branching  nerve-cells  scattered  here  and  there.  The  na- 
ture of  this  matrix  has  been  the  subject  of  dispute  ;  by  some  it  is 
looked  upon  as  connective  tissue  (Kolliker),  by  others  as  neuroglia 
(Virchow).  The  second  and  third  layers  contain  a  large  number 
of  pyramidal,  or  spindle-shaped  cells  ;  of  these  layers  the  third  is 
the  broadest,  and  contains  the  largest  (but  fewest)  cells.  The  cells 
of  the  second  layer  are  about  -j-g^u^o  of  an  inch  in  diameter,  and  are 
closely  pressed  together  to  form  its  substance  ;  but  in  the  third 
layer  they  augment  gradually  in  size  until  they  reach  a  diameter  of 
tt/oF'  ^o  perhaps  gi^  of  an  inch,  with  their  long  axes  perpendicu- 
lar to  the  cortical  surface.  The  fourth  layer  contains  large  num- 
bers of  small,  globular,  and  irregularly-shaped  and  branching  cells  ; 
the  fifth,  spindle-shaped  bodies  with  long  tapering  processes,  and 
also  a  certain  number  of  smaller  irregular  cells.  This  innermost 
layer  consists  chiefly  of  a  compact  accumulation  of  cells  which  give 
'  In  Strieker's  Human  and  Comparative  Anatomy,  11.,  p.  381. 


96 


THE   CEEEBEAL   COETEX. 


off  lateral  processes.  Gerlach  discovers  here,  as  in  the  spinal  cord 
(see  §  9),  a  very  minute  network  with  which  these  processes  are 
apparently  continuous.  It  is  also  an  assumption,  verified  by  direct 
observation  of  some  cases,  and  by  the  general  analogy  of  the  nervous 
system,  that  many  of  the  extremely  attenuated  nerve-fibrils  which 


El  i  ! 


,'W.  ^ii  ''■',.■' 


3C 


Fig.  37. — Section  through  the  Cerebral  Cortex  of  Man,  prepared  with  Osmio  Acid  ^sy^^ 
(Schwalbe.)  /,  principal  external,  and  //.  internal,  layer  ;  x,  laj'er  lying  as  a  limit  between  the 
two  ;  »M,  medullary  substance  sending  out  bundles  of  nerve-tibres  into  //;  i,  layer  poor  in  cells, 
but  with  an  external  plexus  of  nerve-fibres  {Id)  ;  ^,  layer  of  small,  and  3,  of  large,  pyramidal 
cells ;  k,  inner  layer  of  small  nerve-cells. 

radiate  from  the  white  core  of  the  convolutions  are  continuous  with 
the  basal  axis-cylinder  processes  of  the  cells  in  the  layers  of  gray 
substance.  Small  rounded  corpuscles  and  small  stellate  cells,  so 
pellucid  that  they  seem  to  be  only  free  nuclei,  are  contained  in  the 
neuroglia  of  the  gray  substance  of  the  cerebral  cortex.     It  is  doubt- 


WHITE   SUBSTAjSTCE   OF   THE   HEMISPHERES.  97 

ful  whether  these  are  true  nervous  elements  or  not.  The  number 
of  nerve-cells  in  the  cortical  substance  is  very  great.  In  a  portion 
of  this  substance,  only  one  millimeter  square  and  J^-  millimeter 
thick,  100  to  120  have,  on  an  average,  been  counted.' 

Modifications  of  the  arrangement  which  prevails  in  most  of  the 
gray  substance  of  the  hemisjpheres  of  the  brain  are  found  in  certain 
regions.  In  the  cortex  of  the  occipital  lobe  the  number  of  layers 
is  increased  by  the  intercalation  of  additional  granule  layers  to 
seven  or  eight.  In  the  cortex  of  the  Island  of  Eeil,  and  of  the  con- 
volutions bounding  the  Fissure  of  Sylvius,  a  large  proportion  of 
fusiform  cells  is  found.  In  the  fourth  layer  of  the  cerebral  cortex 
of  the  dog,  in  the  region  which  Hitzig  considei'ed  to  be  motor, 
Betz  discovered  certain  cells  lying  in  scattei-ed  groups,  with  two 
large  and  several  small  processes  ;  these  cells,  on  acccount  of  their 
great  size,  he  called  "  giant-cells:"  Similar  cells,  have  been  found 
by  him  in  certain  regions  of  the  human  cerebral  cortex — namely,  in 
the  entire  anterior  central,  and  the  upper  end  of  the  posterior  cen- 
tral convolutions,  and  along  the  lobe  which  is  prolonged  backward 
from  the  two. 

§  28.  The  white  substance  of  the  hemispheres  of  the  brain  may 
all  be  considered  as  originating  in  its  cortical  gray  substance  ;  but 
the  nerve-fibres  of  which  it  is  composed  constitute  three  classes, 
according  to  the  destination  of  the  fascicles  into  which  the  fibres  are 
gathered.  These  three  are  the  down-going  or  peduncular,  the  com- 
missural, and  the  arcuate  (or  fibres  2droprice).  It  is  the  business  of 
the  peduncular  system  to  connect  the  cerebrum  with  the  lower  parts 
of  the  encephalon.  This  system,  called  the  corona  I'adiata,  is  nar- 
rowed into  the  internal  capsule  and  continued  downward  to  the 
crura  cerebri ;  its  diminished  size  shows  that  a  considerable  por- 
tion of  its  fibres  have  entered  into  the  optic  thalami  and  striate 
bodies.  But  it  is  also  probable  that  many  fibres  of  the  crusta  pass 
directly  into  the  brain's  medullary  centre,  and  through  this  to  its 
gray  cortex,  without  entering  these  ganglia.  Of  such  tracts  the 
best  known  is  the  loyramidal  (probably  motor).  According  to 
Flechsig  and  others,  this  is  traceable  through  the  internal  capsule 
and  corona  radiata  to  certain  frontal  and  parietal  convolutions. 
Another  tract,  traceable  directly  to  the  convolutions  of  the  cortex, 
passes  from  the  external  part  of  the  crusta  into  the  white  matter 
of  the  occipital  lobe  (so-called  direct  sensory  tract).  The  fibres 
which  come  from  the  tegmentum,  and  are  lost,  for  the  most  pai-t,  in 
the  thalamus  and  the  subthalamic  region,  stream  outward  from  the 
other  side  of  this  organ,  join  the  general  system  of  the  corona  radi- 
'  See  Luys,  The  Brain  and  its  Functions,  p.  17.  New  York,  1883. 
7 


98  THE    CEREBRAL    CORTEX, 

ata,  and  diverge  to  nearly  every  part  of  tlie  hemispheres  ;  but  espe- 
cially to  the  temporo-sphenoidal  and  occipital  lobes  (probably  sen- 
sory). 

The  commissural  system  of  fibres  has  hitherto  universally  been 
supposed  to  connect  the  two  hemispheres  of  the  brain  ;  but  Pro- 
fessor Hamilton,  of  xiberdeen,  and  others,  have  recently  called  this 
statement  in  question.  The  principal  tract  of  such  fibres  is  in  the 
coi-pus  callosum.  Since  this  commissure  lies  in  a  plane  above  that 
of  the  corona  radiata,  the  two  systems  of  fibres  intersect  each  other 
on  their  way  to  the  convolutions  of  the  cerebral  hemispheres.  A 
smaller  commissure  (the  anterior)  passes  below  the  lenticular  nuclei 
of  the  striate  bodies  and  connects  the  convolutions  around  the  Syl- 
vian fissure — binding  together  the  right  and  left  temporo-sphen- 
oidal lobes  ;  it  also  furnishes  a  root  of  origin  for  the  olfactory 
nerve. 

The  arcuate  fibres  extend  over  more  or  less  territory  on  the 
same  side,  and  connect  the  gray  matter  of  adjacent,  or  more  or 
less  distant,  convolutions  in  the  same  hemisphere — "  a  garland-like 
interweaving  "  of  two  convolutions  around  the  sulcus  between  them. 
In  certain  localities,  where  the  fascicles  into  which  these  fibres  are 
gathered  are  strongly  marked,  they  have  received  special  names  ; 
such  are  the  fasciculus  uncinatus  which  crosses  the  bottom  of  the 
Sylvian  fissure  and  connects  the  convolutions  of  the  frontal  with 
those  of  the  temj)oro-splienoidal  lobe  ;  the  fillet  of  the  gyrus  forni- 
catus,  extending  longitudinally  in  that  convolution  ;  the  longitudi- 
nal inferior  fasciculus,  connecting  the  convolutions  of  the  occipital 
and  temporo-sphenoidal  lobes.  Such  fibi-es  are  sometimes  called 
longitudinal  or  collateral  fibres.  It  is  by  the  commissural  and  arcu- 
ate fibres  that  the  innumei-able  ganglion-cells  and  nerve-granules  of 
the  cortex  are  bound  into  a  unity  of  form  and  of  function.  The  pro- 
cesses of  the  cells  anastomose,  and  are  thus  united  with  immedi- 
ately adjoining  cells  by  means  of  a  gray  fibre-plexus.  The  axis- 
cylinder  processes  become  continuous  with  the  meduUated  fibres, 
which,  gathered  into  bundles  (the  fasciculi  of  the  arcuate  fibres), 
line  as  a  continuous  layer  the  inner  surface  of  the  cortex.  In  this 
manner  the  nervous  elements  of  that  crowning  mechanism,  which 
is  known  as  the  chief  glory  of  man's  nervous  system,  are  made  to 
exhibit  a  manifoldness,  and  at  the  same  time  a  unity  of  structure, 
suggestive  of  a  common  service  joined  with  diversity  of  mode  in 
Avhich  the  service  is  rendered. 

§  29.  The  view  of  Meynert — to  which  reference  has  already  been 
made  (p.  73) — regards  the  gray  masses  and  converging  and  diverg- 
ing tracts  of  the  cerebro- spinal  nervous  mechanism  as  a  "  Projec- 


MEYIS'EET'S   PEOJECTIOJST   SYSTEMS. 


99 


tion  System  "  (or  rather  as  a  series  of  "projection  systems"),  wliich 
is  capped  and  dominated  by  the  hemispheres  of  the  cerebrum.  The 
sensory  nerves  may  thus  be  figuratively  described  as  the  "  feelers," 
and  the  motor  nerves  as  the  "  arms  "  of  its  cortical  gray  matter. 
This  matter  is  both  a  "sensory  shell,"  upon  which  the  centripetal 
nerve-commotions  gather  and  dispose  themselves  ;  aud  is  also  the 
"motor  shell"  in  which  certain  centrifugal  motions  originate.  It 
is,  therefore,  an  internal  "  Projection  Field  "  for  the  muscular  sys- 


Ccl'    ^'"ft 


Fig.  3S. — Median  Section  of  the  Brain.  A,  aqueduct  of  Sylvius :  Cba,  white  commissure  ;  Cbl, 
cerebellum  ;  Oca,  corpus  albicans  ;  Ccl,  corpus  cailosum,  of  which  the  different  parts  are  Ccl', 
rostrum,  CcP,  the  genu,  Ccls,  the  body,  and  Ccl^,  splenium  ;  On,  conarium,  or  pineal  gland; 
Coa,  anterior.  Com,  middle,  and  Cop.  posterior,  commissures ;  PM,  foramen  of  Monro ;  Fta, 
the  anterior,  and  Ftii,  the  posterior,  transverse  fissures ;  Let,  lamina  cinerea  terminalis ;  and 
Lq,  lamina  of  the  corpora  quadrigemina  :  Mo,  medulla  oblongata  :  P,  pons  Varolii ;  SI,  septum 
lucidum ;  SM,  sulcus-  of  Monro ;  Tc,  tuber  cinereum  ;  Vma.  anterior  velum  medullare  ;  V, 
fourth  ventricle ;  II,  optic  nerve  ;  II',  chiasm  of  the  optic  nerve. 

tern.  The  gray  masses  of  the  brain  below  its  hemispheres  (with 
the  exception  of  the  internal  tubular  mass)  may — according  to 
Meynert — be  described  as  either  (a)  "Interruption  Masses"  of  the 
projection  system,  or  as  belonging  to  (b)  the  "  Region  of  Reduc- 
tion "  of  the  mass  of  this  system.  It  is  in  these  lower  gray  masses 
that  the  great  bulk  of  the  nerve-tracts  (the  corona  radiata)  coming 
from  the  cortex  of  the  cerebrum  are  not  only  broken  and  inter- 
rupted in  their  course,  but  are  also  greatly  reduced  in  size.'     The 

'  For  a  clear  and  concise  summary  of  Meynert's  entire  view,   see  Quain's 
Anatomy,  ninth  edition,  ii.,  pp.  370  ff. 


100 


NERVES   OF   THE   CEREBRO-SPINAL   SYSTEM. 


functional  significance  of  this  relation  in  which  the  cerebral  cortex 
stands  to  all  the  rest  of  the  nervous  mechanism  will  appear  more 
clearl}'  further  on  in  the  discussion. 

§  30.  The  cerebro-spinal  axis,  or  central  nervous  mechanism  of 
the  cavit}^  of  the  spinal  column  and  skull,  is  connected  with  the 
end-organs  of  motion  and  of  sense  by  thirty-one  pairs  of  Spinal, 
and  twelve  pairs  of  Cranial  or  Encephalic  Nerves. 

The  thirty-oue  pairs  of  Spinal  Nerves  originate  in  the  spinal 
cord  and  pass  out  of  the  spinal  canal  through  the  openings  called 

C 


Fig.  39.— Posterior  View  of  the  Spinal  Cord  with  its  Nerven.  }4.  (After  Sappey. )  I- VIII  in  A 
are  cervical :  I,  II,  and  III  in  A,  and  IV-XII  in  U,  dor.sal  ;  the  last  in  B,  and  down  to  V  in  C, 
lumbar:  I-V  in  C,  Bacnil  ;  lu,  in,  origin  of  the  posterior  roots;  11,  11,  posterior  median  tis- 
sure  ;  12,  19,  spinal  pan^lia  :  i;j,  13,  united  i).  rve  ;  15,  tapering  of  the  lower  end,  becoming  16, 
10,  the  filum  terininale  ;  IT,  caudii  equina. 

"intervertebral  foramina."  Of  the  entire  number — enumerating 
from  above — eight  pairs  are  cervical,  twelve  thoracic  or  dorsal, 
five  lumbar,  five  sacral,  one  coccygeal.  Each  nerve  arises  from  the 
side  of  the  cord  by  two  roots,  an  anterior  and  a  posterior.  The 
posterior  root  has  a  swelling  or  ganglion  upon  it,  the  anterior  has 
none  ;  the  former  is  composed  of  sensory  nerve-fibres,  the  latter. 


THE  TWELVE   PAIRS    OF   CRAlSriAL  NEEVES.  101 

of  motor  nerve-fibres.  The  ganglion  of  the  posterior  roots  contains 
unipolar  nerve- cells.  The  roots  themselves  vary,  in  the  different 
regions  of  the  cord,  both  as  respects  direction  and  length.  Imme- 
diately outside  the  ganglion  the  anterior  root  joins  the  posterior, 
and  the  united  nerve — containing  a  mixture  of  motor  and  sensory 
fibres — soon  after  separates  into  two  divisions,  that  are  formed  of 
elements  from  each  root  and  that  are  distributed,  one  upon  the 
back  and  the  other  upon  the  front  and  sides,  to  all  parts  of  the 
trunk  and  limbs. 

Of  the  twelve  pairs  (adopting  the  Continental  instead  of  the 
English  division)  of  Cranial  Nerves,  which  arise  fi-om  the  base  of 
the  encephalon  and  pass  thi'ough  the  openings  (foramina)  in  the 
floor  of  the  cranial  cavity,  three  groups  may  be  distinguished  :  (a) 
the  sensor}'  nerves,  or  nerves  of  special  sense  ;  (b)  the  motor  nerves  ; 
(c)  the  mixed  nerves,  which  contain  both  sensory  and  motor  fibres. 
To  the  first  grouj)  belong  the  olfactory  nerve  (first  pair),  the  optic 
(second  pair),  and  the  auditory  (eighth  pair) ;  to  the  second  group 
belong  the  nerves  that  supply  the  principal  muscles  of  the  eyeball 
(oculo-motor,  third  pair),  the  superior  oblique  (trochlear,  foui'th 
pair),  and  external  rectus  (abducent,  sixth  pair),  muscles  of  the  eye, 
the  muscles  of  facial  expression  (seventh  pair),  the  muscles  of  the 
tongue  (hypoglossal,  twelfth  pair),  and  the  spinal  accessory  nerve 
(eleventh  pair)  ;  to  the  third  group  belong  the  three  nerves  which 
are  so  widely  distributed  over  the  mucous  membranes  and  muscles 
of  the  face,  tongue,  pharynx,  and  internal  organs — namely,  the  tri- 
geminus (fifth  pair),  the  glossoj)haryngeal  (ninth  pair),  and  the  pneu- 
mogastric  or  vagus  (tenth  pair). 

§  31.  It  is,  then,  by  a  process  of  differentiation  of  a  few  compara- 
tively simple  elements,  and  of  infinitely  varied  arrangement  and 
combination  of  the  elements  thus  differentiated,  that  the  elaborate 
mechanism  of  the  human  nervous  system  is  constructed,  and  made 
fit  for  the  great  variety  of  interconnected  functions  which  it  is 
called  upon  to  jDerform.  Material  atoms  are  chemically  united  into 
the  comjDlex  and  unstable  molecules  of  which  nervous  matter  is  com- 
posed. These  molecules  are  arranged  into  the  structural  forms  of 
nerve-fibres  and  nerve-cells  ;  and  the  lattei",  at  least,  are  modified 
in  form  according  to  their  location,  and  perhaps  also  function. 
The  elements  are  combined  into  conducting  cords,  end-organs,  and 
central  organs,  according  to  the  threefold  plan  of  a  nervous  sys- 
tem ;  and  the  organs  are  arranged,  in  the  case  of  man,  with  an  in- 
tricacy of  relations  which  can  be  only  very  inadequately  described. 

The  description  of  the  mechanism  being  finished,  we  consider 
more  in  detail  what  it  can  do. 


CHAPTER  III. 
THE  NERVES  AS  CONDUCTORS. 

§  1.  In  that  threefold  economy  of  organs  which  characterizes  the 
developed  nervous  mechanism,  the  office  of  propagating  the  neural 
process  between  the  central  organs  and  the  end-organs  has  been 
assigned  to  the  nerves.  The  power  to  originate  this  process  under 
the  action  of  external  stimuli,  although  experiment  shows  that  it 
belongs  to  the  nerves,  is  not  exercised  by  them  while  in  their  nor- 
mal place  within  the  mechanism.  It  is  the  office  of  the  end-organs 
to  transmute  the  physical  molecular  processes,  which  are  their  stim- 
uli, into  the  physiological  and  neural  process,  and  hand  it  over,  as  it 
were,  to  these  conducting  cords.  But  the  office  of  the  nerves  as 
conductors  is,  of  course,  not  like  that  of  a  tube  which  conducts  along 
its  channel  some  kind  of  fluid,  nor  is  it  like  that  of  the  wire  or  bell- 
metal  which  is  thrown  into  vibration  throughout.  It  is  a  molecular 
commotion  which,  when  started  at  any  point  in  the  nerves,  moves 
in  both  directions  from  point  to  point  along  its  course.  The 
intimate  connection  between  the  two  functions  of  excitation  and 
conduction  becomes,  then,  at  once  apparent.  Indeed,  excitation 
may  be  considered  as  the  setting  uj)  of  the  process  of  conduction  ; 
conduction  as  the  uninterrupted  continuance,  or  propagation  from 
point  to  i^oint,  successively,  of  the  process  of  excitation.  Each 
minute  subdivision  of  the  nerve,  then,  must  be  regarded  as  consti- 
tuting, in  some  soi't,  a  source  or  centre  of  stimulation  with  respect 
to  its  neighboring  subdivisions.  If  the  nerve-commotion  is  to 
move  along  the  nerve  N,  between  two  distant  portions  of  its  struct- 
ure, a  and  z,  then  a  must  act  upon  its  neighbor  6  as  a  stimulus,  b 
upon  c,  and  so  on  successively  until  y  is  found  stimulating  z,  and 
the  process  of  progressive  excitation  or  conduction  is  complete. 

§  2.  It  follows  from  what  has  just  been  said  that,  in  considering 
the  nerves  as  conductors,  the  conditions  and  laws  of  the  origination 
of  that  process  of  excitation  which  they  conduct  must  be  taken  into 
account.  It  is  neither  necessary  nor  convenient,  however,  to  carry 
throughout  a  distinction  between  the  two  functions — the  excitabil- 
ity and  the  conductivity — of  the  nerves ;  it  is  better  to  regard  them 


QENERAL   PHYSIOLOGY   OF   NERVES.  103 

as  one  process  from  somewhat  different  points  of  view.  The  arising 
and  progressive  movement  of  a  unique  molecular  commotion  con- 
stitutes the  distinctively  neural  action  or  function  of  the  nerves. 
And  since  this  so-called  nerve-commotion  has  eluded  all  the  at- 
tempts hitherto  made  to  discover  its  more  intimate  nature,  and  to 
bring  it  under  a  strict  theory,  we  must  be  content  with  describing 
the  following  three  classes  of  facts  :  (1)  The  Conditions  of  the  pro- 
cess ;  (2)  the  Phenomena  evoked  with  it,  or  as  part  of  it,  by  differ- 
ent kinds  of  stimuli ;  (3)  the  Laws  of  its  propagation. 

What  is  called  "  the  genei'al  physiology  of  nerves "  attempts  to 
consider  their  action  while  excluding  the  influence  upon  it  from 
the  central  organs  aud  the  end-organs.  That  is,  the  function  of  the 
nerves,  as  we  now  consider  it,  is  exercised  under  ahnormal  conditions. 
It  has  been  objected  to  the  view  which  regards  each  element  of 
the  nerve  as  the  stimulus  of  neighboring  elements,  that  the  ef- 
fects of  direct  artificial  stimulation  must  differ  in  important  respects 
from  those  obtained  by  stimulation  in  the  normal  way.  For  exam- 
ple, Ziemssen  and  others  have  shown  that  the  crushed  nerve  of  an 
animal,  or  the  paralyzed  nerve  of  a  man,  may  be  made  to  set  up  a 
nerve-process  hy  reflex  stimulation  when  it  will  no  longer  respond 
to  stimulation  applied  directly  to  its  trunk.  And  Grtinhagen  af- 
firms that  after  a  stretch  of  nerve  has  been  reduced  by  the  effects 
of  carbonic  acid  to  a  lower  degree  of  excitability  under  direct  stim- 
ulation, it  will  still  propagate  through  itself  the  excitation  set 
up  elsewhere  with  undiminished  force.  Such  facts,  however,  only 
prove  that  the  application  of  stimuli  to  the  nerve  for  purposes  of 
experiment  is  a  very  rough  and  ineffective  way  compared  with  nat- 
ure's method  of  preparing  the  stimuli  by  the  modifying  influence 
of  the  nervous  tissues  themselves.  They  do  not  prove  that  the 
neural  process  is  not  fundamentally  the  same  in  whatever  way  it  is 
brought  about.  On  the  contrary,  there  is  abundant  evidence  to 
show  that  this  abnormal  activity,  when  carefully  studied,  will  give 
us  the  key  to  the  normal  function  of  the  nerves.  The  advantages 
of  simplifying  the  problem  by  experiments  upon  isolated  nerves 
are  too  great,  and  the  fund  of  valid  information  thus  obtained  is 
too  important  for  us  to  neglect  the  method  proposed.  The  science 
called  "  genei'al  physiology  of  the  nerves  "  is,  indeed,  very  largely 
built  upon  experiments  with  the  motor  nerves  of  frogs  ;  and,  of 
course,  it  may  be  said  that  frogs,  with  respect  to  their  nervous  sys- 
tems as  otherwise,  are  very  unlike  men.  But  with  respect  to  the 
character  of  that  specific  molecular  process  which  is  set  up  in  the 
nerve  when  excited,  frogs  apjDcar  to  be  essentially  the  same  as  men. 
At  any  rate,  we  have  no  physical  means  adequate  for  detecting  any 


104  THE  NERVES   AS   CONDUCTORS. 

essential  differences.  In  other  words,  nerves  are  nerves  the  world 
over  ;  and  what  they  do  as  nerves  simply,  is  essentially  one  thing  in 
all  cases.  What  they  do  in  their  vastly  different  arrangements  and 
connections  with  central  organs  and  end-ox"gans  differs  vastly  in 
different  cases. 

§  3.  The  view  that  each  element  of  every  nerve,  irrespective  of 
its  kind  or  specific  place  in  the  animal  mechanism,  can  only  stimu- 
late its  neighbor  and  be  stimulated  by  its  neighbor,  suggests  an- 
other interesting  inquiry.  Is  this  stimulus  of  the  nerve-elements, 
this  effect  in  exciting  contiguous  elements,  aniologous  to  any  of  the 
so-called  external  stimuli  ?  Or,  in  other  words,  the  inquiry  may  be 
raised :  Is  the  process  of  nerve-commotion  in  the  nerves  similar  to, 
or  identical  with,  any  of  those  molecular  processes  which  act  as  in- 
direct stimuli  upon  the  nerves  through  the  end  organs  ?  In  answer- 
ing this  question  it  has  long  been  customary  to  ally  nerve-commo- 
tion with  electricity.  In  a  posthumous  work  b}''  the  mathematician 
Hansen,  in  1743,  it  was  first  proposed  to  consider  the  efficient 
j)rinciple  of  nervous  action  as  identical  with  that  of  the  electrical 
machine.'  Exactly  a  century  later  (1843)  du  Bois-Reymond  an- 
nounced the  discovery  of  an  electrical  current  in  unexcited  nerves 
(the  so-called  "  current  of  rest ").  Since  then  the  phenomena  of  this 
current,  of  the  negative  variation  of  the  nerve,  and  of  electrotonus 
— all  discovered  almost  simultaneously  by  the  same  investigator — 
have  been  the  subject  of  much  painstaking  research.  This  research 
has  resulted  in  showing  that  important  differences  exist  between 
the  neural  process  and  that  of  the  electrical  current,  and  in  making 
more  and  more  clear  the  impossibility  of  forming  a  purely  electri- 
cal theory  of  the  nervous  functions.  On  the  other  hand,  it  has  also 
revealed  many  important  similarities  between  the  two.  It  is  by 
experiment  with  the  effect  of  electrical  currents,  of  different  kinds 
and  directions,  and  under  varying  conditions,  that  the  science  of 
general  physiology  of  the  nerves  has  been  built  up. 

§  4.  In  order  to  understand  the  general  results  of  experiment 
upon  the  nerves,  the  nature  and  use  of  the  so-called  Nerve-muscle 
Ilachine  must  be  understood. 

A  "nerve-muscle  preparation"  consists  of  muscle  freshly  taken 
from  the  living  animal  with  its  attached  nerve  dissected  out ;  for 
example,  the  gastrocnemius  muscle  of  the  frog  with  the  attached 
sciatic  nerve.  Such  a  preparation  may  be  kept  alive  for  some  time 
in  a  moist  chamber.     By  the  simple  contrivance  of  connecting  the 

'  See  in  du  Bois-Reymond's  great  work  the  history  of  opinions  on  this 
point :  Untersucltuiigen  iiber  thieriache  Electricitiit,  11. .  i.  ,pp.  209  ff.  Berlin, 
Vi49. 


THE   IN'EEVE-MUSCLE   MACHINE.  105 

end  of  the  muscle  with  a  lever,  arming  the  lever  with  some  means 
of  making  a  mark — either  pen,  or  bristle,  or  needle — and  bringing 
its  point  thus  armed  to  bear  on  a  rapidly  travelling  surface  (plain 
paper,  or  smoked  paper,  or  glass),  the  time  and  amount  of  the  con- 
tractions of  the  muscle  may  be  recorded.  The  most  refined  means 
for  noting  the  exact  instant  when  the  stimulus  is  applied,  and  also 
the  state  of  the  effects  produced  at  every  succeeding  instant  of  their 
duration,  are  of  first  importance.  The  nerve  may  be  stimulated 
with  different  kinds,  degrees,  and  directions  of  the  electrical  cur- 
rent (or  with  other  forms  of  stimuli)  at  any  points  preferred  in  its 
stretch,  and  under  a  great  variety  of  conditions  with  respect  to  tem- 
perature, moisture,  mechanical  pressure  or  stricture,  integrity  and 
vitality  of  its  structure,  etc.  ;  and  the  effects  of  such  stimulations 
upon  the  contractions  of  the  muscle  may  be  noted  and  compared 
as  they  have  been  recorded.  Means  for  testing  the  most  delicate 
and  rapid  changes  in  the  electrical  or  thermometric  conditions  of 
the  nerve  may  be  applied  to  it  at  any  point  of  its  stretch.  Varia- 
tions and  refinements  of  experiments  essentially  the  same  may  be 
almost  indefinitely  multiplied  ;  the  experiments  may  be  repeated, 
and  verified  or  corrected,  by  the  same  observer  or  by  others.  In- 
asmuch as  the  preparation  is  both  muscle  and  nerve,  an  acquaint- 
ance with  the  behavior  of  the  muscle,  and  with  the  laws  of  its  con- 
traction, is  necessary  in  order  that  it  may  be  known  how  much  of 
the  complex  phenomena  is  to  be  ascribed  to  the  functional  activity 
of  muscle,  how  much  to  that  of  nerve.  But  into  a  statement  of  the 
general  laws  of  contractile  tissues,  and  of  the  nature  and  explana- 
tion of  the  behavior  of  muscle  when  irritated,  we  cannot  enter.' 

Certain  terms  in  constant  use  to  describe  the  methods  and  results 
of  experiments  with  the  nerve-muscle  machine  also  require  a  brief 
explanation.  The  line  traced  by  the  armed  end  of  the  lever,  as  it 
rises  and  falls  with  the  contractions  of  the  muscle,  is  known  as  the 
"  muscle-curve."  In  so  far  as  it  shows  changes  that  are  due  to  the 
condition  of  the  attached  nerve,  or  to  the  quality,  intensity,  and 
order  of  the  stimulations  applied  to  that  nerve,  this  curve  is  a 
measure  of  the  process  of  neural  excitation  and  conduction.  If 
the  electrical  current  flows  with  the  course  of  the  motor  nerve- 
stretch — that  is,  from  the  central  toward  the  'oeripheral  parts — it 
is  called  "  descending,"  or  direct  ;  if  in  the  opposite  direction 
"  ascending,"  or  inverse.     The  current  to  be  detected  in  an  unex- 

'  For  a  description  of  the  method  and  results  of  experimenting  with  the 
nerve-muscle  preparation,  more  accessible  to  the  general  reader  than  the  books 
to  which  reference  will  chiefly  be  made,  see  Foster's  Text-book  of  Physiology, 
pp.  43  ff. 


106  THE  NERVES   AS   CONDUCTOKS. 

cited  nerve  (a  nerve,  that  is,  whose  functional  activity  is  not  at  the 
time  in  exercise  on  account  of  the  appHcation  of  any  kind  of  stim- 
lus)  is  called  a  "  natural  current,"  or  a  "  current  of  rest."  The  cur- 
rent produced  by  stimulating  the  nerve,  and  so  calling  into  exer- 
cise its  physiological  function,  is  a  "current  of  action."  When 
a  single  induction-shock,  or  a  number  of  such  shocks  repeated 
at  sufficient  intervals,  is  sent  through  a  nerve-stretch,  the  contrac- 
tile spasm  of  the  muscle  in  response  to  each  shock  shows  that 
a  single  "nervous  impulse  "  is  passing  along  the  nerve.  When  the 
single  stimulations  are  repeated  with  sufficient  rapidity,  the  single 
spasms  fuse  into  one  apparently  continuous  effort,  known  as  "  tet- 
anus," or  "tetanic  contraction."  The  term  "tetanus"  applies 
primarily  to  the  muscle  only  ;  but  the  application  of  rajDidly  re- 
peated shocks  to  the  nerve,  such  as  would  produce  "tetanic  con- 
traction "  of  the  muscle,  may  be  called  the  "  tetanization  of  a  nerve." 
The  contraction  which  follows  the  closing  of  the  current  is  called 
the  "making  contraction,"  or  "closing  contraction;"  that  which 
follows  its  opening,  the  "bi'eaking"  or  "opening"  contraction. 

§  5.  Of  the  conditions  under  which  alone  the  nerve  is  capable  of 
exercising  its  function  of  neurility  the  most  important  are  these 
three  :  Vitality,  Oxygen,  and  Recovery  from  previous  exhaustion. 

A  nerve  cannot  act  as  a  conductor  of  the  neural  process  unless 
it  is  vital ;  but  the  death  of  the  nerve  is  not  necessarily  simultane- 
ous with  that  of  the  body  from  which  it  is  taken,  or  of  the  muscle 
to  which  it  is  attached.  On  the  contrary,  by  careful  treatment  with 
respect  to  moisture  and  temperature,  and  by  guarding  it  from 
mechanical  or  chemical  injury,  it  may  be  preserved  alive  for  some 
time  after  excision.  The  indirect  irritability  of  the  muscle  through 
the  excised  nerve  attached  to  it  frequently  continues  in  warm- 
blooded animals  and  in  high  temperature  not  longer  than  about 
an  hour  ;  in  the  frog  and  in  a  low  tempei'ature  it  may  last  for  sev- 
eral days.  The  nerves  of  the  summer  frog  are  much  more  perish- 
able than  those  of  the  same  animal  in  winter.  A  nerve  is,  of  course, 
alive  as  long  as  it  will  excite  the  muscle  to  contract.  But  the  nerve 
is  not  necessarily  dead  when  the  attached  muscle  no  longer  resjDouds 
to  its  excitation  ;  the  failure  may  be  due  to  the  death  of  the  very 
sensitive  and  perishable  end-organs  which  connect  the  two.  Her- 
mann *  considered  that  the  existence  of  electrical  phenomena  in  the 
nerves  of  rabbits  showed  the  nerves  to  be  alive  for  several  hours 
after  they  would  no  longer  stimulate  the  muscle,  and  also  after  the 
muscle  itself  could  not  be  irritated  directly.  Nerves  may  even  be 
alive  after  they  cease  to  exhibit  electrical  phenomena  that  can  be 
1  Handb.  d.  Physiol.,  II.,  i.,  p.  120. 


VITALITY    AT^D  DYING   OF   THE   NERVE.  107 

eletected  by  the  most  delicate  tests  available.  It  is  possible  that 
the  capacity  for  excitation  may  linger  after  the  capacity  for  con- 
ducting the  excitation  is  lost.  Since  the  nerve,  unlike  the  muscle, 
has  no  death-rigor,  we  cannot  say  just  when  it  is  wholly  dead. 

During  the  stages  of  dying,  nerves  exhibit  two  interesting  changes 
of  excitability.  Immediately  after  it  is  severed  from  the  body 
the  irritability  of  the  nerve  increases  temporarily,  and  afterward 
diminishes  by  successive  degrees  until  it  is  wholly  lost.  The 
course  of  these  changes  in  its  irritability  is  found  to  be  different 
for  different  parts  of  the  same  nerve-sti*etch.  It  was  discovered  by 
Valli  and  Ritter  '  that  a  nerve  which  has  once  ceased  to  stimulate 
its  attached  muscle  to  contract  will  again  excite  muscular  contrac- 
tion if  the  electrodes  be  applied  farther  down  its  stretch  ;  there- 
fore the  lower  portion  of  the  nerve-stretch  seems  to  preserve  a 
given  degree  of  vitality  for  the  longest  time.  From  this  fact  "  Valli's 
principle "  has  been  derived :  Nerves  die  from  the  centre  to  the 
periphery.  The  temporary  increase  of  the  irritability  of  the  ex- 
cised nerve  belongs  indeed  to  its  entire  stretch  ;  but  it  appears  first 
in  the  upper  part.  This  fact  is  connected  with  the  important  in- 
fluence which  the  cross-section  of  a  nerve  has  upon  its  electrical 
and  neural  condition.  As  to  the  reason  for  this  increase  of  nervous 
excitability  which  accompanies  the  first  stage  in  the  dying  of  the 
nerve,  we  are  quite  in  the  dark. 

§  6.  Closely  allied  to  the  foregoing  changes  are  those  which  take 
place  in  the  structure  and  functional  activity  of  a  nerve  that  re- 
mains in  the  living  animal  organism  after  having  been  separated 
from  the  central  organs.  Such  a  nerve,  after  a  time,  completely 
loses  its  irritability.  Two  investigators,  Giinther  and  Schon,"  found 
this  time  to  be,  in  the  case  of  rabbits  or  dogs,  about  three  or  four 
days  ;  in  a  cold-blooded  animal  like  the  frog,  the  time  may  be  pro- 
longed to  a  week,  or  even  more.  The  law  of  increased  irritability, 
produced  in  the  entire  nerve-stretch,  but  first  manifested  in  the 
portion  nearest  the  cross-section,  immediately  after  separation  from 
the  central  organ,  holds  good  for  most  observations  on  nerves  cut 
in  situ  ;  its  application  is  obvious,  however,  only  to  the  case  of  the 
motor  nerves.  In  1850  Waller  announced  '  the  discovery  that  the 
anatomical  changes  (a  fatty  or  granular  degeneration)  which  take 
place  in  the  nerve-fibres  after  being  severed  from  the  central  organs 
proceed  fi.-om  the  place  of  section  to  the  extreme  peripheral  portion 

1  See  in  du  Bois-Rejinond's  Untersuchungen,  etc.,  i.,  pp.  321  ff. 

2  See  the  Archiv  f.  Anat.  Physiol.,  etc.,  1840,  p.  270. 

^  In  Philosophical  Transactions,  1850,  ii.,  p.  423;  and  see,  also,  Archiv  f. 
\nat.  u.  Physiol.,  1852,  p.  392. 


108  THE   NERVES   AS   CONDUCTORS. 

of  the  fibre ;  and  that  the  sensory  nerves  do  not  degenerate  in  theii 
peripheral,  but  in  their  central  portion,  when  the  posterior  roots 
are  cut  above  the  ganglion.  The  central  portion  of  the  nerve,  when 
cut  at  a  point  lying  toward  the  periphery  from  the  ganglion,  may 
be  shown  (in  the  case  of  the  sensory  nerves,  which  alone  admit  of 
being  experimented  upon  for  this  purpose)  to  retain  its  irritability 
for  a  long  time,  although  it  finally  loses  it  through  lack  of  exercise. 
A  cut  nerve  remaining  in  situ  may  be  regenerated,  and  so  regain  its 
functional  jDowers.  Regeneration  takes  place  by  the  axis-cylinders 
growing  out  from  the  central  portion  and  running  into  and  between 
the  sheaths  of  Schwann  of  the  peripheral  portion  ;  it  is  accom- 
plished, then,  by  the  influence  of  the  central  organs.  The  irrita- 
bility of  the  nerve  returns  as  its  structure  is  regenerated.  Accord- 
ing to  some  investigators  its  conductivity  is  regained  earlier  than 
its  power  of  local  irritability.  Duchenne  '  and  others  claim  that 
the  influence  of  the  will  is  the  first  form  of  stimulus  to  regain  con- 
trol of  regenerated  motor  fibres. 

§  7.  Oxygen,  as  furnished  by  the  circulation  of  the  arterial  blood, 
is  the  second  condition  for  the  performance  by  the  nerves  of  their 
distinctive  functions.  But  nerves,  as  compared  with  the  central 
organs  or  end-organs  of  the  nervous  system,  or  even  with  the  mus- 
cles, are  relatively  independent  of  the  presence  of  oxygen.  Indeed, 
since  the  muscle  is  so  much  more  sensitive  to  changes  in  the  qual- 
ity of  the  blood,  and  is  supplied  by  the  same  arteries  that  supply 
the  attached  nerves  ;  and  since  the  irritability  of  the  nerve  is  tested 
by  the  vital  contraction  of  the  muscle — it  is  difiicult  to  determine 
by  experiment  the  exact  effect  upon  the  nerves  of  withdrawing 
from  them  the  oxygen  of  the  blood.  The  irritability  of  the  nerves 
continues  about  as  long  in  a  moist  vacuum,  or  in  indifferent  gases, 
as  in  the  air.  What  little  is  known  of  the  chemical  processes 
which  take  place  ir.  the  nerves  confirms  the  view  that  they  are  rel- 
atively independent  of  the  presence  of  oxygen  ;  and  the  experi- 
ments of  Severini,  who  thinks  that  he  has  discovered  a  restorative 
effect  of  ozone  (if  not  of  ordinary  oxygeu)  upon  these  organs  when 
dying,  are  not  yet  fully  confirmed.  It  may  be  argued,  however, 
from  the  marked  dependence  of  the  other  forms  of  nervous  tissue 
upon  a  supply  of  arterial  blood,  as  well  as  from  the  general  theory 
of  the  nervous  system,  that  the  presence  of  some  oxygen  is  a  nec- 
essary condition  of  the  functional  activity  of  the  nerves. 

§  8.  Exhaustion  is  a  condition  of  the  nerves  recovery  from  which 
is  necessary  in  order  that  they  may  exercise  their  normal  functions  ; 
but  exhaustion  of  the  nerves  is  difiicult  to  distinguish  experimen- 
'  Traitu  de  I'clectrisatiou  localisee,  second  edition.     Paris,  1861. 


MECHAlSriCAL   PROPERTIES   OF   NERVES.  109 

tally  from  exhaustion  of  the  central  organs  or  of  the  end-organs. 
The  experiments  of  du  Bois-Eeymond  upon  the  negative  varia- 
tion of  the  nerve-current  under  repeated  irritation  give  us  the 
first  item  of  the  desired  proof.  The  variation  under  these  circum- 
stances becomes  constantly  weaker.  By  ingeniously  separating  the 
proofs  of  exhaustion  in  the  muscle  from  those  of  exhaustion  in  the 
nerve,  Bernstein  '  has  shown  that  the  latter  comes  on  much  more 
slowly  than  the  former ;  and  that  by  far  the  greater  amount  of 
the  effects  attributed  to  exhaustion  in  the  nerve-muscle  macliine 
belong  to  the  muscle-element  of  this  machine.  When  tired,  how- 
ever, the  nerve  recovers  more  slowly  than  the  muscle.  Nerve- 
cells — and  therefore  the  central  oi-gans  and  end-organs  of  the  ner- 
vous mechanism — tire  much  more  easily  and  quickly  than  nerve- 
fibres.  Indeed,  according  to  Hermann,"  it  is  conceivable  that  all 
the  phenomena  of  exhaustion  which  take  place  in  the  normal  expe- 
rience of  the  nervous  system  belong  really  to  the  organs  connected 
with  the  nerves  rather  than  to  the  nerves  themselves.  When  we 
are  tired  nervously,  it  is  not  ordinarily  the  nerves  that  are  tired. 
And  yet  the  law  of  the  exhaustion  and  recovery  of  functional  ac- 
tivity doubtless  belongs  to  normal,  as  it  does  to  excised,  nerve-fibres. 

§  9.  The  various  classes  of  phenomena  which  are  evoked  in  con- 
nection with  the  starting  and  propagation  of  nerve-commotion 
along  a  nerve-stretch  will  be  considered  from  two  points  of  view  : 
First,  as  regards  their  dependence  upon  the  character,  amount,  and 
method  of  the  application  of  the  stimuli  which  are  used  ;  and,  sec- 
ond, as  indicative  of  certain  processes — chemical,  thermic,  electri- 
cal, etc. — ^set  up  in  the  nerves  themselves.  We  shall  thus,  as  far 
as  possible,  avoid  repetition. 

§  10.  The  mechanical  properties  of  the  nerves  are  of  little  inter- 
est to  psycho-physical  researches  ;  and  comparatively  little  con- 
cerning their  physiological  functions  has  been  learned  by  the  ap- 
plication to  them  of  mechanical  stimuli.  The  elasticity  of  nerves 
in  the  dead  body  was  found  by  Wertheim  to  follow  the  same  laws 
as  that  of  the  muscle — their  absolute  ductility  is  less  than  that  of 
muscle  ;  their  cohesion  greater.  All  kinds  of  mechanical  attacks  on 
the  nerves  excite  them,  and  are  followed  by  pain  in  the  case  of 
sensory  nerves,  contraction  of  the  muscles  in  the  case  of  motor 
nerves.  By  rapid  shocks  of  this  kind — for  example,  with  a  toothed 
wheel  or  a  hammer — tetanus  may  be  produced.  A  certain  sudden- 
ness of  influence  is,  in  general,  necessary  to  the  effect.  Yet  Pon- 
tana  succeeded  in  cutting  nerves  very  quickly  with  a  sharp  knife 
without  producing  any  muscular  conti-action.     Pi'essure  of  a  neiwe 

'In  Pfliiger's  Arcliiv,  xv.,  p.  289  f.  "Handb.  d.  Physiol.,  II.,  i.,  p.  135. 


110  THE   NERVES   AS   CONDUCTORS. 

may  be  increased  very  gradually  to  a  high  degree  without  exciting 
it ;  but  its  jDower  of  conductivity  is  thus  temi^orarily  suspended. 
Veiy  moderate  jDressure  or  slight  traction  of  the  nerve  has  been 
found  by  several  investigators  to  increase,  at  least  for  a  moment, 
the  irritability  of  the  nerve  ;  and  perhaps,  also,  the  speed  of  con- 
duction in  it.  All  neural  function  is,  of  course,  destroyed  by  any 
considerable  mechanical  injury  of  the  nerve,  such  as  often  happens 
by  stricture  or  pressure  from  a  swelling. 

§  11.  IViermfc  influences  upon  the  phenomena  of  the  neural  pro- 
cess are  very  marked  and  important.  On  the  other  hand,  almost 
nothing  is  known  as  to  the  specific  heat  of  nerves  or  as  to  their 
power  to  conduct  heat.  Hermann  thinks  it  probable  that  the 
latter  is  different  in  the  two  main  directions  of  the  fibres.  The 
results  of  experiment  differ  as  to  the  degree  of  heat  which  is  neces- 
sary to  act  upon  the  nerves  as  a  stimulus.  Valentin,  the  first  ob- 
server in  this  line,  found  that  clipping  the  motor  nerves  of  frogs 
in  water  heated  to  about  100°  Fahr.  (38°  C.)  caused  contractions ; 
but  Eckhard  obtained  such  results  only  from  temperatures  above 
150.8°  to  154.4°,  or  below  25°  to  22°— that  is,  temperatures  that 
are  either  deadly  or  permanently  injurious  to  the  nerve.  Nor, 
according  to  the  latter,  is  the  nerve  excited  by  changes  in  tempera- 
ture as  it  is  by  changes  in  the  electrical  current.  Slighter  changes 
near  the  dead-line  may  have  an  effect  to  excite  the  nerve  ;  but  con- 
siderable changes  in  the  medium  temperatures,  as  a  rule,  have  no 
such  effect.  It  is  the  opinion  of  some,  however,  that  such  thermic 
changes,  when  marked  and  sudden,  may  act  as  a  stimulus  to  mo- 
tor nerves.  It  Avas  shown  by  E.  H.  Weber '  that  heat  and  cold  have 
no  effect  in  producing  sensations  when  applied  directly  to  the  sen- 
sory nerve-trunks  of  man. 

While  there  is  little  evidence,  then,  to  show  the  direct  excitatory 
effect  of  heat  upon  the  nerves,  there  is  no  doubt  whatever  as  to 
the  importance  of  thermic  influences  upon  their  excitability  and 
conductivity.  High  degrees  of  temperature  may  destroy  the  pow- 
er of  the  nei've  to  perform  its  functions,  but  without  killing  it. 
Warmth  increases  the  immediate  expenditure  of  energy  in  an  ex- 
cised nerve,  and  so  hastens  its  death ;  cold  delays  this  expenditure, 
and  so  conserves  the  nerve.  The  limit  of  this  increased  irritability 
of  the  nerve  under  the  influence  of  heat  is  reached  at  about  122° 
Fahr.  ;  as  the  degree  of  heat  applied  rises  from  this  point  toward 
150°,  its  effect  is  rapidly  felt  in  causing  the  death  of  the  nerve. 
Sudden  cooling  from  about  68°  down  to  50°  may  produce  a  tem- 

'  In  Wagner's  Handworterb.  d.  Physiol.,  III.,  ii.,  pp.  496,  578  ;  and  Archiv 
f.  Anat.,  Physiol.,  etc.,  1847,  p.  342,  1849,  p.  273. 


EFFECT   OF   CHEMICAL   INFLUENCES.  Ill 

porary  rise  of  irritability  ;  but,  in  general,  cooling  below  59°  di- 
minishes the  irritability  of  nerves.  The  effect  of  temperature  upon 
the  speed  of  conduction  will  be  referred  to  elsewhei-e. 

§  12.  Chemical  influences  have,  for  the  most  part,  surprisingly 
little  effect  upon  the  irritability  and  conductivity  of  the  nerves, 
especially  in  view  of  their  great  sensitiveness  to  other  external  in- 
fluences. Such  indifference  is  probably  due  to  the  protection  of 
the  nerve  by  its  membranes.  The  effect  of  most  chemical  agents, 
when  long  continued,  is  to  destroy  the  nerve  without  irritating  it ; 
but  some  agents  in  a  concentrated  form  act  upon  it  as  stimuli. 
The  researches  of  Eckhard,  KoUiker,  and  Ktlhne  have  given  us 
most  of  the  information  we  have  upon  this  matter.  Only  two 
points  need  mention  here.  First :  Changes  of  the  amount  of  water 
in  the  substance  of  the  nerve  affect  its  functional  activity.  Drying 
the  nerve  produces  contractions  ending  in  tetanus  ;  although,  ac- 
cording to  some  authorities,  these  effects  do  not  follow  if  the  dry- 
ing be  very  sudden.  A.  slight  amount  of  drying  raises  temporarily 
the  irritability  of  the  nerve.  The  amount  of  the  decrease  of  water 
necessary  to  produce  contractions  in  the  attached  muscle  is  given 
by  Birkner  at  four  to  eight  per  cent,  of  the  weight  of  the  nerve ; 
irritability  ceases,  although  the  dried  nerve  is  not  dead,  with  a 
loss  of  forty  per  cent.  Others,  however,  give  the  latter  figure  as 
between  eight  per  cent,  and  nineteen  per  cent.  Swelling  the  nerve 
in  water  or  other  indifferent  fluids  decreases  its  irritability  slowly 
to  the  point  of  entire  cessation. 

Second :  The  effect  of  certain  acid  and  alkaline  solutions  upon 
the  nerve  is  much  hke  that  of  drying  it.  Various  neutral  salt  so- 
lutions, and  free  alkalies  in  solution,  produce  strong  muscular  con- 
tractions, ending  in  tetanus  and  death.  Certain  organic  sub- 
stances in  concentrated  solutions — for  example,  urea,  sugar,  and 
glj^cerine — irritate  the  nerve  ;  so,  according  to  most  observers,  does 
alcohol  of  from  ninety  per  cent,  to  eighty  per  cent.  The  law  seems 
to  be,  that  all  chemical  stimulation  of  the  nerves  is  closely  connected 
with  the  destruction  of  the  nervous  tissue. 

§  13.  The  phenomena  evoked  by  applying  the  stimulus  of  elec- 
tricity to  the  nerve-muscle  machine  are  very  numerous  and  diffi- 
cult of  disentanglement,  since  they  depend  upon  such  a  variety  of 
changing  conditions.  Following  is  a  y&cj  brief  statement  of  some 
of  the  more  important  of  such  phenomena,  in  as  far  as  they  relate 
to  the  direct  excitatory  effect  of  this  stimulus,  and  also  to  its  effect 
in  modifying  the  excitability  of  the  nerve.' 

'  Here,  as  throughout  the  subject  of  the  general  physiology  of  the  nerves, 
the  chief  reliance  has  been  placed  upon  Hermann,  Handb.  d.  Physiol.,  II.,  i. 


112  THE  ISTERVES   AS    CONDFCTOES. 

The  resistance  which  living  nerves  oifer  to  the  electrical  current 
does  not  differ  much  from  that  of  living  muscle  ;  it  is  given  by 
most  authorities  as  somewhat  greater.  According  to  Weber's  in- 
vestigationp  its  resistance  is  about  50,000,000  times  as  great  as 
that  of  copper  wire.  According  to  Harless,  the  conductivity  of  the 
nerve  is  on  the  average  about  14.86  times  that  of  distilled  water. 
Hermann  found  the  conductivity  to  be  much  greater  in  the  longi- 
tudinal than  in  the  transverse  direction  of  the  nerve. 

As  to  the  direct  excitatory  effect  upon  the  nerve  of  constant 
currents  and  of  their  variations,  the  main  principle  is  that  formu- 
lated by  du  Bois-Reymond  in  1845.*  This  principle  may  be  stated 
as  follows  :  The  excitatory  effect  of  the  constant  current,  as  judged 
by  the  contraction-curve  of  the  muscle,  does  not  correspond  to  the 
absolute  value  of  the  intensity  of  the  current  at  each  moment, 
but  to  the  change  in  this  value  from  one  moment  to  another  ;  and 
the  effect  is  greater  the  less  the  time  in  which  changes  of  the  same 
magnitude  in  the  current  occur,  or  the  greater  their  magnitude  in 
the  same  length  of  time.  The  essential  fact  is  that  constant  cur- 
rents, while  they  remain  constant,  do  not  irritate  the  nerve  ;  vari- 
ations in  such  currents  do  irritate  it.  The  variation  may  be  either 
frovi  zero  or  to  zero  (the  making  or  the  breaking  of  the  current), 
but  it  must  have  a  certain  degree  of  suddenness  to  be  of  any  effect. 
Hence  induction-shocks  are,  relatively  to  their  actual  strength, 
much  more  effective  than  the  constant  current  in  exciting  the 
nerve.  Great  difficulties,  however,  stand  in  the  way  of  stating 
definitely  the  relations  that  exist  between  variations  in  the  strength 
of  the  constant  current  and  changes  in  the  excitation  of  the  nerve 
produced  by  these  variations ;  Hermann,  indeed,  pronounces  the 
difficulties  "insuperable." 

It  is  not  absolutely  certain  that  the  constant  cvxrrent  itself,  apart 
from  variations  in  its  strength,  has  any  excitatory  effect  upon  the 
sensory  nerves.  The  sensory  effects  produced  bj  such  a  current, — 
for  example,  pain  in  the  skin,  roaring  in  the  ears,  sensations  of 
light  and  color,  electrical  taste,  giddiness  (as  when  the  current  is 
passed  transversely  through  the  head  at  the  mastoid  processes), 
etc. — are  due  to  the  end-organs  and  the  central  organs.  It  is  per- 
haps probable  that  such  a  current  itself  may  produce  tetanus  in 
certain  nerves  ;  but  the  effect  is  very  small  compared  with  that 
produced  by  variations  of  this  current,    Pfluger  found  tetanus  pro- 

'  In  a  paper  communicated  to  the  Physiological  Society  in  Berlin,  August 
8th,  of  that  year ;  see,  also,  his  Untersuchungen  uber  thierische  Electricitat, 
I.,  p.  25». 


DIRECTIOlSr    OF  THE   CURRENT. 


113 


duced  by  weak  currents  of  about  tlie  order  of  the  so-called  muscle- 
current  ;  but  not  by  strong  ones. 

§  14.  The  excitatory  effect  of  the  constant  current  is  dependent 
upon  its  direction.  If  three  grades  of  strength  are  assigned  to  all 
sacli  currents — namely,  weak,  medium,  and  strong — the  results  of 
all  the  experimenters  will  be  found  to  agree  as  to  the  dependence 
of  the  effect  of  medium  and  strong  currents  upon  their  direction  ; 
as  to  the  case  of  weak  currents,  authorities  differ.  The  following 
table,  given  by  Pfliiger,'  states  the  conclusion  agreed  to  by  the 
larger  number  of  observers  : 


Ascending  Current. 

Descending  Current. 

Making. 

Breaking. 

Making. 

Breaking. 

Weak 

Medium 

Contraction. 
Contraction. 
Rest. 

Rest. 

Contraction. 

Contraction. 

(Contraction. 
Contraction. 
Contraction. 

Rest. 
Contraction. 

Strong 

Rest  or  weak 

contraction. 

The  results  here  tabulated  are  obtained  by  experimenting  with 
the  excised  motor  nerves  of  frogs.  In  experiments  with  the  sen- 
sory nerves,  or  with  any  of  the  nerves  while  remaining  in  the  liv- 
ing animal,  the  conditions  become  so  complicated  that  satisfactory 
results  in  confirmation  of  Pfliiger's  conclusions  have  not  yet  been 
reached. 

§  15.  The  excitatory  effect  of  the  constant  current  is  also  depend- 
ent upon  its  absolute  strength.  Du  Bois-Reymond,  after  discovering 
his  law,  proceeded  to  raise  the  inquir}^  whether  the  height  of  the 
current  upon  which  the  variation  is  piled  up,  as  it  were,  has  any 
influence  upon  its  effect.  Various  attempts  to  answer  the  inquiry 
have  been  made  ;  but  the  discovery  of  Pfliiger's  laAv  of  electvotonus 
has,  according  to  Hermann,''  changed  the  form  of  the  question  to 
the  following :  What  influence  upon  the  excitatory  effect  of  in- 
creasing catalectrotonus  and  diminishing  anelectrotonus  does  the 
absolute  amount  of  existing  electrotonus  have  ?  In  this  form  it  will 
be  referred  to  again. 

§  16.  The  excitatory  effect  of  the  electrical  current  is  influenced 
by  the  length  of  the  nerve-stretch  through  which  it  flows.  From 
the  beginning  of  electro-physiology  the  opinion  has  prevailed  that 
the  excitatory  effect  is  increased  by  the  length  of  the  nerve-stretch. 
This  view  accords  theoretically  with  deductions  from  Pfluger's  law 
of  electrotonus.  The  experimental  proof,  however,  is  somewhat 
vacillating ;    in  part,  doubtless,  on  account  of    the   admixture  of 

'  See  Untersuchungen  iiber  die  Physiologie  d.   Electrotonus,  p.  453.     Ber- 
lin, 1859.  ^  Haudb.  d.  PliysioL,  II.,  i.,  p.  76. 
8 


114  THE   ]srERVES   AS   COE^DUCTORS. 

different  local  conditions  where  different  considerable  lengths  of  a 
nerve  are  passed  through.  Different  investigators  have  found  the 
increase  of  irritability  in  the  nerve,  as  dependent  upon  its  length, 
confined  within  different  limits ;  one  has  fixed  the  limit  at  from 
jig  to  ^  inch,  another  at  from  ^  to  f  inch.  Willy  found  the  rule, 
in  general,  to  hold  good  only  for  descending  currents. 

§  17.  The  excitatory  effect  of  a  constant  current  is  influenced  by 
the  angle  between  the  axis  of  the  nerve  and  the  direction  of  the 
current.  After  considerable  experimentation,  Avith  varying  results, 
the  more  modern  researches  have,  according  to  careful  experiments 
made  by  Albrecht  and  A.  Meyer,  in  the  laboratory  of  Hermann,' 
confirmed  the  opinion  of  Galvani :  The  electrical  current  does  not 
excite  the  nerve  when  it  flows  precisely  at  right  angles  to  the 
nerve's  axis. 

§  18.  The  duration  of  the  current  also  influences  its  effect  as  a 
stimulus. 

Attention  has  already  been  called  to  the  exhausting  effects  of 
long-continued  stimulation  of  the  nerve,  whether  by  electricity  or 
otherwise.  But  can  a  shock  be  so  brief  as  not  to  stimulate  the 
nerve  at  all?  The  reason  why  vei-y  brief  currents,  on  breaking  the 
circuit,  are  not  followed  by  a  contraction  of  the  muscle  is  obvi- 
ously to  be  found  in  the  fact  that  the  condition  of  anelectrotonus, 
on  which  the  breaking  conti'action  depends,  has  not  had  time  to 
develop  itself.  But  J.  Konig,  working  under  Helmholtz's  direc- 
tion, found  that  currents  which  would  produce  the  making  but  not 
the  breaking  contraction,  j)rovided  they  had  sufficient  duration,  pro- 
duced no  contractions  at  all  if  they  lasted  only  0.001  of  a  second. 
On  increasing  the  duration  of  the  current  the  strength  of  the  con- 
tractions increased  also,  until  at  0.017-0.018  of  a  second  they 
reached  the  same  height  as  that  of  the  contraction  produced  by  the 
corresponding  constant  ciu'rent.  It  may  be  said,  then,  that  the 
electrical  current  must  act  uj)on  a  nerve  for  at  least  about  0.001^ 
of  a  second  in  order  to  excite  it.  The  nerve  on  being  cooled 
becomes  more  sluggish  in  its  resj)onse  to  the  stimulus  ;  at  the 
freezing-point  it  requires  a  duration  of  nearly  0.02  of  a  second  for 
the  stimulus  to  start  it  into  action. 

§  19.  Besides  the  direct  excitatory  effect  upon  the  nerve  of  elec- 
trical currents,  we  have  to  consider  their  effect  in  modifying  the 
action  of  the  nerve  under  stimuli,  whether  electrical  or  of  some 
other  kind.  If  a  nerve-stretch  is  under  the  influence  of  a  constant 
current  which  is  being  passed  through  it,  the  effect  of  stimuli, 
when  applied  to  any  part  of  the  nerve  and  judged  by  sensation  or 
'  See  his  Handb.  d.  Physiol,,  II.,  i.,  p.  81  f. 


pfluger's  law  of  electrotontjs.  116 

muscular  contraction,  is  increased.  This  changed  condition  of  the 
nerve  with  respect  to  its  excitabihty,  which  the  electrical  current 
produces,  is  called  "  Electrotonus."  The  term  was  introduced  into 
physiology  by  du  Bois-Eeymond,  who  was  preceded  in  his  in- 
vestigations by  Kitter,  Nobili,  and  Matteucci,  and  followed  by 
Valentin,  Eckhard,  and  others.  It  is  Pfliiger,  however,  who  is  en- 
titled to  have  his  name  permanently  attached  to  the  law  of  elec- 
trotonus; for  it  is  he  who  most  thoroughly  analyzed  the  facts, 
separated  the  variables  from  the  constants,  and  gave  scientific  form 
to  the  result.  It  is  found  that  the  modified  excitability  of  the 
electrotonized  nerve  (that  is,  of  the  nerve  which  has  been  thrown 
by  the  passage  of  the  electrical  current  into  this  modified  condition 
of  excitability)  is  not  uniform  through  its  entire  stretch,  but  is 
greatest  in  the  immediate  region  where  the  electrodes  are  applied. 
Moreover,  it  differs  at  the  two  electrodes — the  condition  at  the 
anode  (or  positive  pole)  from  that  at  the  cathode  (or  negative  pole). 
It  differs,  also,  for  that  part  of  the  stretch  which  lies  between  the 
electrodes  as  compared  w^ith  that  which  is  outside  of  the  electrodes. 
Pfluger's  law  states  the  whole  case  as  follows  :  The  excitability  of  a 
nerve  under  the  action  of  the  constant  current  is  increased  in  the 
catelectrotonized  region  (that  is,  on  both  sides  of  the  negative  elec- 
trode), and  diminished  in  the  anelectrotonized  region  (that  is,  on  both 
sides  of  the  positive  electrode).  This  law  is  declared  by  Hermann ' 
to  hold  good  of  all  kinds  of  stimulus,  and  in  all  cases — with  the  only 
ajDparent  exception  of  the  suprapolar  region  of  an  ascending  current. 
This  electrotonic  eifect  of  the  constant  current,  like  its  direct 
excitatory  effect,  is  influenced  by  the  strength  of  the  current,  by  its 
making  and  breaking,  and  by  the  length  of  the  stretch  through 
which  it  flows.  The  change  in  the  excitability  of  the  electrotonized 
nerve  increases  with  the  strength  of  the  current,  from  the  low- 
est observable  point  until  it  soon  reaches  a  maximum ;  after  this 
maximum  is  reached,  further  increase  of  electrotonus  is  to  be  rec- 
ognized only  by  the  expanding  of  this  condition  over  the  extra- 
polar  parts  of  the  nerve-stretch.  Electrotonus  increases  also  with 
the  length  of  the  nerve-stretch  affected ;  but  this  relation  also 
finally  reaches  a  maximum.  Electrotonic  changes  in  the  catelec- 
trotonic  region  occur  immediately  upon  making  the  current ;  they 
then  speedily  but  slightly  increase,  and  more  slowly  diminish  again. 
The  anelectrotonic  condition  develops  and  extends  itself  compar- 
atively slowly,  reaches  a  maximum,  and  then  gradually  falls  off 
again.  The  immediate  consequence  of  breaking  the  current  is  to 
increase  the  electrotonic  condition  of  the  nerve  in  the  anelectrotonic 
'  Handb.  d.  Physiol.,  II.,  i.,  p.  43. 


116  THE   NERVES    AS    CONDUCTORS. 

region,  and  very  briefly  to  decrease  it  in  tlie  catelectrotonic  region  5 
the  former  increase  gradually  vanishes ;  the  latter  decrease  is  fol- 
lowed, after  a  few  seconds,  hj  an  increase  which  lasts  from  one- 
half  a  minute  to  fifteen  minutes. 

The  so-called  "laws  of  electrotonus "  are  almost  wholly  based 
"upon  esjDeriments  with  the  motor  nerves  of  frogs.  Great  and  even 
insuperable  difficulties  stand  in  the  way  of  proving  experimentally 
its  application  to  sensory  nerves,  or  to  the  nerves  of  living  and  self- 
conscious  man.  The  conditions  of  influence — from  the  central 
organs  and  end-organs,  from  sensation  and  will — upon  the  nerves 
in  such  cases  are  so  complicated  as  to  bafile  all  attempts  to  analyze 
them  by  means  of  direct  experimentation. 

Further  consideration  of  electrotonus,  and  of  its  bearing  upon 
a  mechanical  theory  of  the  nerves,  must  be  for  the  present  post- 
poned. 

§  20.  The  phenomena  evoked  in  connection  with  the  starting 
and  propagating  of  nerve-commotion  along  a  nerve-stretch  may  be 
presented — in  the  second  place  (see  §  9) — as  indicative  of  certain 
Processes  set  up  within  the  nerves  themselves.  That  the  effect 
of  a  constant  current  is  not  exhausted  in  direct  excitation  of  the 
nerve  is  proved  by  the  changed  condition  of  excitabiUty  which  it 
also  produces. 

No  mechanical  process  that  can  be  made  directly  appreciable  by 
the  senses  or  accurately  measured  by  mechanical  means,  like  that 
which  takes  place  in  the  contracting  muscle,  occurs  in  the  nerve 
when  excited  to  its  physiological  activity  by  means  of  appropriate 
stimuli.  Whatever  changes  then  take  place  in  it  are  invisible  and 
impalpable. 

§  21.  Nor  are  we  much  better  able,  on  the  ground  of  experi- 
mental tests,  to  affirm  the  existence  of  any  thermic  process  in 
connection  wdth  the  excitation  of  the  nerves.  If  any  rise  of  tem- 
perature in  the  nerve  is  caused  by  the  application  of  stimulus,  it 
is  exceedingly  small.  Helmholz,^  in  connection  with  his  investiga- 
tions into  the  heating  of  the  muscle  when  in  a  state  of  tetanus, 
could  detect  no  development  of  heat  in  the  nerve,  although  his 
means  would  have  revealed  a  change  of  only  a  few  thousandths  of 
a  degree.  On  the  other  hand,  Schiff  and  Heidenhain  both  de- 
tected a  rise  of  temperature  in  the  brain  due  to  nervous  excitation. 
But  it  is  still  a  question  how  far  this  fact  indicates  anything  more 
than  change  in  the  distribution  of  the  arterial  blood.  Moreover, 
the  former  of  the  two  observers  failed  to  obtain  any  evidence  of 
heating  in  the  cerebellum  by  sensory  excitation.  The  ease  of  the 
'  Archiv  f.  Anat,  Physiol.,  etc.,  1848,  p.  158. 


THE   KATUEAL   ISTERVE-CURRENT.  Il7 

conducting  nerve-cords  and  that  of  the  cellular  tissue  of  the  cen- 
tral organs  may  very  likely  be  different  in  this  regard. 

§  22.  Nor  have  any  chemical  processes  been  indubitably  proved 
to  occur  in  the  nerves  as  an  accompaniment  or  result  of  the  exez'- 
cise  of  their  physiological  function.  The  only  experimental  evi- 
dence of  such  a  process  is  the  change  of  reaction  which  some  ob- 
servers have  found.  Funke  and  others  have  asserted  that,  not  only 
a  certain  time  after  death,  but  also  after  exertion  as  caused  by 
cramping  produced  with  strychnine-poisoning,  the  nerves  show  an 
acid  reaction.  But  Heidenhain  and  other  observers  contest  this 
alleged  fact.  Other  assertions  of  chemical  changes  set  up  in  the 
nerves  by  exciting  them  are  even  more  uncertain.  Eanke's  theory 
of  a  "respiration  of  the  nerves"  is  quite  without  any  sufficient  ex- 
perimental proof  ;  and  so  is  his  claim  that  an  absorption  of  the 
water  of  the  nervous  tissue  results  from  tetanus.  If  any  chemical 
changes  are  produced  in  the  nerve  by  exciting  it,  they  are  like  the 
thermic — exceedingly  small.  This  fact  is  proved  by  the  almost 
comjDlete  independence  of  the  nerve  with  respect  to  the  oxygen 
of  the  arterial  blood,  and  by  the  absence  of  any  observable  changes 
in  its  temperature  when  functionally  active.  But  here  again  we 
must  distinguish  between  the  case  of  the  nerves  as  conductors  and 
that  of  the  nervous  tissue  of  the  central  organs. 

§23.  Evidence  of  the  electrical  j^rocess  in  nerves  functionally  ac- 
tive is  not  wanting.  It  was  not,  however,  until  the  discovery  of  du 
Bois  Eeymond,  announced  in  1843,  that  any  experimental  evidence 
had  been  obtained  to  show  the  existence  of  electrical  currents  in 
the  nerves,  although  it  had  previously  been  conjectured  that  the 
distinctively  neural  process  is  a  phase  of  electricity.  This  ex- 
perimenter found  that  in  the  case  of  the  nerve,  as  in  that  of  the 
muscle,  the  cross- section  artificially  made  is  negative  toward  the 
longitudinal  surface  of  the  nerve-stretch.  Weak  longitudinal  cur- 
rents also  show  themselves  between  the  two  cross-sections  of  a 
nerve-stretch  thus  prepared.  The  current  outside  the  nerve-stretch 
may  be  considered  as  completed  by  a  current  in  the  nerve-stretch 
from  its  cut  end  to  the  equator.  This  current  (called  "natural 
nerve-current,"  or  "  current  of  rest ")  is  the  same  in  the  sensory, 
the  motor,  and  the  mixed  nerves  of  the  same  animal  ;  but  its  elec- 
tro-motive force  is  greater  the  larger  and  thicker  the  nerve.  Its 
absolute  strength  in  the  sciatic  nerve  of  the  frog  is  given  by  du 
Bois-Eeymond  as  0.022  of  a  Daniell's  cell,  but  by  Engelmann  as 
0.046.  It  gradually  becomes  extinct  in  the  nerves  of  the  dead 
body,  but  it  continues  for  some  time  after  their  irritability  is  lost. 

The  same  discoverer,  du  Bois-Eeymond,  found  that  the  current 


118  THE   NERVES   AS    CONDUCTOES. 

of  rest  is  diminished  in  energy  by  tetanizing  the  nerve-stretch  with 
an  electrical  current.  That  is,  if  when  one  of  the  electrodes  is  placed 
at  the  equator,  and  the  other  at  the  cut  end  of  a  nerve-stretch,  the 
needle  of  the  galvanometer  indicates  the  passage  of  a  so-called  cur- 
rent of  rest,  and  then  the  muscle  to  which  the  nerve  is  attached  be 
tetanized  by  passing  an  interrupted  current  through  the  nerve,  the 
needle  will  swing  back  toward  zero.  This  variation  is  called  the 
"negative  variation  "  of  the  nerve-current.  It  may  be  produced  by 
chemical  and  mechanical,  as  well  as  by  electrical,  stimulation ;  and 
when  the  nerve  is  no  longer  irritable  the  negative  variation  sinks 
to  zero.  It  shows,  therefore,  that  the  electro-motive  force  of  the 
nerve  is  diminished  by  the  nerve  being  excited ;  and  the  degree 
of  the  negative  variation  is  a  measure  of  this  diminution,  although 
it  does  not  wholly  nullify  the  so-called  current  of  rest.  The  nega- 
tive variation  of  the  electrical  current  in  the  nerve  is  closely  con- 
nected with  the  nerve-commotion  which  is  started  and  conducted 
in  the  nerve.  Since  the  excitation  of  the  nerve  is  known  to  be 
progressive,  or  of  a  wave-like  character,  the  nature  of  this  connec- 
tion, according  to  Hermann,  may  be  more  definitely  stated  as  fol- 
lows :  The  electrical  condition  of  each  excited  place  in  a  nerve- 
stretch  is  negative  toward  all  the  places  of  the  same  nerve-fibre 
that  are  unexcited.  Hence,  between  any  two  points  in  a  nerve- 
fibre,  while  the  nerve-commotion  is  passing  over  the  distance,  two 
phases  of  the  current  of  action  occur  ;  the  first  phase  is  in  the 
same  direction  as  the  course  of  the  wave  of  excitation,  the  second 
is  in  the  opposite  direction. 

§  24.  The  Laws  which  are  known  to  govern  the  starting  and  prop- 
agation of  nerve-commotion  along  the  nerves  as  conductors  are 
few  in  number  ;  they  deal  chiefly  with  relations  between  the  mag- 
nitude of  the  stimulus  and  the  amount  of  the  resulting  impulses, 
and  with  the  conditions  for,  and  speed  of,  the  unbroken  propaga- 
tion of  these  impulses. 

The  relations  which  exist  between  the  magnitude  of  the  stimulus 
applied  to  the  nerves  in  their  normal  condition  and  the  amount  of 
resulting  nervous  impulse  cannot  be  given  with  accuracy.  For,  in 
the  first  i^lace,  there  is  no  absolute  measure  for  either  of  the  two 
values  which  it  is  desired  to  compare.  Of  the  various  stimuli 
which  act  upon  the  nerve-fibres,  electricity  is  the  only  one  that  ad- 
mits of  even  a  fairly  approximate  measurement  as  an  excitant  of 
these  fibres  ;  and  the  excitatory  effect  of  electricity  does  not  vary 
in  direct  proportion  to  the  strength  of  the  current,  but  in  propor- 
tion to  the  changes  in  its  strength.  With  reference  to  attaining  a 
direct  measurement  of  the  amount  of  the  process  set  up  in  the 


EFFECT   OF   SEVERAL   EXCITATIOISTS,  119 

nerve  by  the  stimulus,  we  seem  to  be  in  a  yet  more  helpless  con- 
dition. The  effect  of  this  process  is  almost  wholly  manifested-  in 
the  organs  with  which  the  nerve  is  connected  rather  than  in  the 
nerve  itself.  There  is  evidence  in  the  case  of  the  nerves,  however, 
as  in  that  of  the  muscles,  that  their  excitation  consists  in  the  set- 
ting free,  by  the  stimulus,  of  potential  energy  due  to  the  molecular 
constitution  of  the  nerve  itself.  But  the  exact  nature  of  this  en- 
ergy, and  of  its  mathematical  relations,  both  to  the  stimulus  and  to 
the  resulting  energy  called  forth  in  the  organs  connected  with  the 
nerve,  we  shall  probably  never  discover.  Still  further,  as  Griitzner ' 
and  others  have  shown,  the  same  kind  and  degree  of  stimulus  pro- 
duces different  effects  when  applied  to  different  nerves. 

§  25.  Allowing  for  the  uncertain  factors,  however,  some  approxi- 
mate statement  may  be  ventured  as  to  the  i*elation  between  the 
magnitude  of  the  stimulus  and  that  of  the  resulting  nerve-commo- 
tion. Measuring  the  amount  of  the  process  in  the  nerve  by  the 
resulting  contraction  in  the  muscle,  Hermann  °  found  that  this 
amount  increases,  at  first  rapidly  and  then  more  slowly,  with  the 
increase  of  the  stimulus.  According  to  Fick,^  the  height  to  which 
the  lever  is  raised  by  the  contractions  of  the  muscle  varies,  within 
certain  limits,  in  direct  proportion  to  the  amount  of  the  stimulus. 
The  last-mentioned  observer  also  noted  two  remarkable  phenom- 
ena :  (1)  On  increasing  the  amount  of  the  stimulus  beyond  the 
point  necessary  to  produce  the  first  maximum  contraction,  another 
stage  is  reached  in  which  the  effect  further  increases,  in  proportion 
to  the  stimulus,  until  a  second  maximum  is  gained.  (2)  In  some 
circumstances,  after  reaching  the  first  maximum,  the  effect  dimin- 
ishes with  the  increase  of  the  stimulus,  then  rises  on  further  in- 
crease, until  it  attains  a  second  maximum. 

The  effect  of  several  excitations  may  be  supposed  to  pass  along 
the  nerve  as  separate  waves  of  nerve-commotion  ;  but  in  order  to 
keep  the  waves  separate  the  interval  between  them  must  be  more 
than  about  yro  °^  ^  second  (the  fraction  differing  for  different 
nerves,  different  animals,  etc.),  otherwise  they  fuse  in  the  muscle 
and  tetanus  results.  The  combined  effects  of  stimulations  havine 
the  requisite  interval  may  be  piled  up,  or  summed  up,  in  the 
nerve,  and  be  seen  in  superimposed  contractions  of  the  muscle. 
Two  simultaneous  excitations  of  the  same  jplace  of  the  nerve-stretch 
are  thus  "summed  up  "  as  long  as  the  maximum  of  excitation  is 
not  reached ;  the  two  are,  in  fact,  one.     If  the  cathodes  of  the  two 

'  Pfluger's  Arcliiv,  xvii.,  pp.  215  ff. ;  and  xxv.,  pp.  255  ff. 

2  See  Archiv  f.  Anat.  u.  Physiol.,  1861,  p.  392. 

3  Untersuchungen  iiber  electrische  Nerveiireizung.     Braunschweig,  1864. 


120  THE  NERVES  AS  CONDUCTORS. 

exciting  currents  unite,  the  same  effect  takes  place.  A  similar  re- 
sult may  be  gained  by  combining  the  effects  of  two  different  kinds 
of  stimuli — as,  for  example,  electricity  and  the  drying  oft'  of  the 
nerve. 

§  26.  In  a  rough  way  the  specific  excitability  also  of  different 
nerves,  or  of  different  localities  in  the  same  nerve,  may  be  dis- 
covered. Harless  found  that  the  excitability  of  the  nerves  of  the 
frog  is  twenty-two  times  as  great  in  winter  as  in  summer.  In  the 
cut  nerve  it  is  greater  near  the  artificial  cross-section.  Many 
observers  have  contended  that  the  excitability  of  the  normal  nerve 
diminishes  toward  its  peripheral  portion.  Matteucci  investigated 
the  subject  of  local  differences  of  excitability  in  the  sensory  nerves ; 
moi-e  recently  Eutherford '  discovered  that  the  reflex  effects  of 
stimulating  a  sensory  nerve  are  greater  the  nearer  the  central 
organ  the  stimulus  is  applied.  Finall}',  Helmholtz "  and  Hermann ' 
observed  that  the  lower  part  of  the  nerve-stretch  is  more  excitable 
under  the  action  of  an  ascending,  the  upper  under  that  of  a  de- 
scending induction-current. 

§  27.  The  Speed  with  which  the  process  of  conduction  takes 
place  in  the  nerves  has  been  determined  with  considerable  accu- 
racy, under  a  variety  of  circumstances  ;  this,  notwithstanding  the 
fact  that  the  physiologist  Joh.  Miiller'  declared  it  to  be  forever 
impossible  no  longer  ago  than  1844.  In  only  1850,  however, 
Helmholtz  ^  announced  that  he  had  succeeded  in  measuring  the 
speed  of  nervous  impulses  in  the  motor  nerves  of  the  frog.  The 
rate  he  found  to  be  26.4  meters,  or  about  86.6  feet,  per  second. 
Another  series  of  investigations,  in  which  the  pendulum-myograph 
was  used,  gave  a  result  about  3  feet  larger  (27.25  m.).  Subsequent 
investigators  have  substantially  confirmed  the  figures  of  Helm- 
holtz. Bernstein,  by  a  still  different  method  of  measurement,  found 
that  the  speed  of  conduction  in  the  nerves  varies  between  25  and 
33  meters.  In  the  motor  nerves  of  man  the  number  was  still  later 
fixed  by  Helmholtz  and  Baxt  at  33.9  meters,  or  about  111  feet,  per 
second.  Von  Wittich  found  it  to  be  about  98.5  feet  per  second. 
The  complexity  of  the  elements  which  enter  into  the  measurement 
of  the  speed  of  nervous  impulses  in  the  sensorij  nerves  makes  it  neai'- 
ly  impossible  to  obtain  satisfactory  results  by  experiment.  And  so 
far  as  the  calculations  take  into  account  changes  produced  in  the 

1  See  Journal  of  Anat.  and  Physiol.,  1871,  v.,  pp.  329  ff. 

''Archiv  f.  Anat.  u.  Physiol.,  1850,  p.  337. 

^  Pflager's  Archiv,  viii.,  p.  261;   and  xvi.,  p.  262. 

*See  his  Handbuch  der  Physiologie,  i.,  pp.  581  fE.     Coblenz,  1844. 

""See  Archiv  f.  Anat.  u.  Physiol.,  1850,  pp.  276-364. 


.SPEED    OF   NERVOUS   IMPULSES.  121 

nervous  centres  with  accompanying  phenomena  of  sensation  and 
attention,  their  discussion  belongs  elsewhere.  Of  the  four  factors 
that  enter  into  the  entire  time  ("reaction-time")  Avhich  elapses 
between  the  application  of  stimulus  to  a  sensory  nerve  and  the 
resulting  contraction  of  the  muscle — namely,  (1)  time  of  conduction 
in  the  sensory  nerve  ;  (2)  processes  in  the  central  organs  ;  (3)  time  of 
conduction  in  the  motor  nerve  ;  and  (1)  latent  period  of  the  muscle 
— it  is  difficult  to  disentangle  the  factor  (No.  (1)  )  required  by 
the  attempt  at  analysis.  Hirsch,  by  experimenting  with  stimuli  ap- 
plied to  the  skin  at  different  distances  from  the  brain,  found  the 
speed  of  conduction  in  the  sensory  nerves  of  man  to  be  about  111.5 
feet  per  second— a  result  in  exceedingly  close  agreement  with  the 
figure  obtained  by  Helmholtz  for  the  motor  nerves.  Schelske 
used  another  method  of  measurement ;  by  applying  the  stimulus 
to  the  groin  and  the  foot,  and  recording  the  difference  of  time  in 
the  two  classes  of  cases,  he  obtained  results  varying  between 
25.294  and  32.608  meters  per  second.  Others  have  given  figures 
differing  more  or  less  widely  from  those  just  stated.  The  general 
conclusions,  however,  favor  numbers  lying  between  98  and  131 
feet  per  second  as  giving  the  speed  of  conduction  in  the  sensory 
nerves  of  man. 

The  speed  of  conduction  in  all  nerves  depends  upon  several  va- 
rying conditions,  such  as  their  temperature,  the  strength  of  the 
stimulus,  length  of  the  nerve-stretch,  and  its  electrical  condition. 
Experiments  in  winter  give  different  results  from  those  in  summer. 
In  the  motor  nerves  of  man  the  rate  can  be  made,  by  changes  of 
temperature,  to  vary  from  about  98  feet  to  295  feet  per  second. 
It  has  been  disputed  by  different  observers  whether  the  speed  of 
conduction  is  dependent  in  any  degree  uj)on  the  strength  of  the 
stimulus  ;  and  even  Hermann  considers  the  question  undecided. 
But  Vintschgau  '  has  recently  shown,  as  the  result  of  a  large  number 
of  carefully  conducted  experiments,  that  as  soon  as  the  stimulus 
rises  above  a  certain  limit  of  intensity,  the  speed  of  the  nervous 
impulses  increases  with  the  increase  of  the  intensity  of  the  stimulus. 
This  limit  depends,  however,  upon  the  direction  of  the  current,  upon 
whether  it  is  a  making  or  a  breaking  current,  upon  the  animal 
chosen  for  experiment,  etc.  Whether  the  speed  of  the  nervous  im- 
pulses is  directly  dependent  upon  the  length  of  the  nerve-stretch 
is  scarcely  decided  beyond  doubt.  The  effort  of  the  science,  gen- 
eral "nerve-physiology,"  is  directed  toward  showing  how  these 
variations  in  speed,  as  experimentally  determined,  may  be  explained 
from  the  laws  of  Electrotouus. 

>  In  Pfliiger's  Archiv,  1883,  xxx.,  pp.  17  fE. 


122  THE   NERVES   AS   CONDUCTORS. 

§  28.  Finally,  it  sliould  be  remembered  that  the  fact  of  any 
propagation  of  nervous  impulses  whatever  presupposes  the  con- 
tinuity, integrity,  and  isolation  of  the  nerve  tract  along  which  the 
impulses  move.  The  slightest  separation  of  the  substance  of  the 
nerve  by  cross-section,  even  when  the  cut  ends  are  left  in  the 
closest  mechanical  contact,  destroys  the  unity  of  the  nerve's 
phj^siological  function.  The  ancients  knew  that  tying  the  nerve 
prevented  its  action  ;  they  explained  the  fact  by  saying  that  the 
flow  of  nervous  fluid  was  thus  hindered.  So  also  does  the  fineness 
of  the  localization  which  belongs  to  the  organs  of  motion,  but 
especially  to  those  of  sense,  as  well  as  the  fact  that  partial  section 
of  a  nerve  only  lames  part  of  the  field  cared  for  by  that  nerve, 
indicate  the  physiological  isolation  of  the  nerve-fibre  during  its 
course  between  end-organs  and  central  organs.  Since  the  result  of 
stimulating  a  given  nerve  is  in  quality  invariably  the  same,  it  would 
seem  that  the  law  of  the  "  specific  energy  "  of  each  nervous  element 
(to  which  we  shall  leier  elsewhere)  is  connected  with  the  assump- 
tions necessary  to  explain  the  phenomena  attendant  upon  the 
starting  and  propagating  of  nervous  impulses  in  the  conducting 
nerves. 

§  29.  Inasmuch  as  the  central  organs  are  to  a  large  extent  com- 
posed of  nerves,  a  complete  account  of  the  nerves  as  conductors 
should  include  a  description  of  the  nature  of  that  nerve-commotion 
which  is  propagated  from  point  to  point  along  the  nervous  ele- 
ments within  these  organs,  and  of  the  paths  or  tracts  along  which 
it  passes.  But  unfortunately  our  knowledge  upon  these  matters  is 
exceedingly  scanty  and  uncertain.  This  is  in  part  due  to  the  fact 
that  the  influence  of  the  ganglion-cells,  with  which  the  nerve-fibres 
are  mixed  to  form  the  central  organs,  profoundly  modifies  the 
neural  processes  of  excitation  and  conduction.  The  subject  be- 
longs, then,  to  a  consideration  of  the  functions  of  the  central  or- 
gans rather  than  of  the  nerves  alone.  Certain  statements,  how- 
ever, may  most  fitly  be  given  in  this  connection. 

"When  speaking  of  conduction  in  the  spinal  cord  or  brain  we 
are  not  to  think  of  a  nerve-commotion  as  always  moving  along  one 
fixed  path,  after  the  analogy  of  the  far  simpler  case  of  the  nerve  in 
the  nerve-muscle  machine.  It  is  true  that  the  nerve-fibre  in  its 
normal  place  in  the  body  runs  insulated,  as  it  were,  between  the 
spinal  cord  and  the  end-organ  at  the  periphery.  But  the  spinal 
cord  itself  does  not  act  as  a  perfectly  isomorphic  medium.  The 
very  complex  structure  of  this  organ,  in  which  nerve-fibres  and 
nerve-cells  are  intricately  interwoven,  has  already  shown  us  that  it 
is  not  adapted  to  act  as  such  a  medium.     The  case  of  the  brain  is 


IMPULSES   IN   THE   SPINAL  COED.  123 

even  clearer.  It  accords,  therefore,  with  the  structure  of  all  central 
organs,  that  we  should  find  the  speed  of  conduction  slower  in  them 
than  in  the  peripheral  nerves.  Exner '  calculated,  from  thie  delay 
which  sensory  impulses  experience  in  the  cord  of  man,  that  their 
speed  there  is  not  more  than  about  26|-  feet  (8  meters)  per  sec- 
ond. The  speed  of  the  motor  impulses  in  the  cord  he  gives  doubt- 
fully as  varying  between  36  feet  and  49  feet  (11  to  12  and  14  to  15 
meters).  These  numbers  are  substantially  confirmed  by  the  con- 
clusions of  Burckhardt  (8  to  14  meters).  The  latter  also  maintains 
that  the  speed  of  the  impulses  which  occasion  sensations  of  touch  is 
greater  than  that  of  those  which  occasion  pain  (as  27  to  50  meters 
compared  with  8  to  14).  It  has  also  been  observed  that,  in  some 
cases  of  persons  with  disease  of  the  posterior  strands  of  the  spinal 
cord,  sensations  of  pain  arise  in  consciousness  notably  later  than 
those  of  touch.  But  the  interpretation  of  all  these  phenomena  is 
complicated  with  questions  of  the  cerebral  functions  ;  for  sensations 
of  pain  are  pre-eminently  of  cerebral  origin.  Moreover,  we  can 
have  but  meagre  confidence  in  our  ability  to  tell  with  any  pre- 
cision the  length  of  the  paths  by  which  nervous  impulses  travel  in 
the  spinal  cord  of  man.  The  fact  observed  by  du  Bois-Reymond, 
that  the  vibrations  of  the  muscle  tetanized  through  the  cord  are 
less  than  would  be  expected  from  the  number  of  shocks  given  by 
the  stimulus,  and  the  fact  discovered  by  Helmholtz,  that  muscle 
when  tetanized  by  an  act  of  will  has  a  uniform  tone  indicating 
nineteen  vibrations  to  the  second  (the  rate  of  vibration  into  which 
the  muscle  is  thrown  by  direct  stimulation  of  the  motor  nerve,  on 
the  contrary,  corresponding  to  the  number  of  shocks),  show  the 
profound  effect  of  the  central  organs  over  the  nervous  impulses. 
Although,  then,  the  experimental  evidence  is  not  perfectly  conclu- 
sive, it,  on  the  whole,  confirms  what  we  should  expect  from  the 
anatomical  structure  of  the  spinal  cord,  as  to  the  complexity  and 
relative  slowness  of  conduction  in  this  organ. 

§  30.  Various  attempts  have  been  made  by  experimental  physi- 
ology to  demonstrate  the  paths  of  conduction  in  the  spinal  cord. 
The  evidence  from  histology  on  this  difiicult  subject  has  already 
been  given  (p.  71  f.).  It  is  not  always  easy  to  make  the  two  lines 
of  evidence  coincide.  As  to  one  point  of  experimental  physiology^ 
however,  no  doubt  has  existed  since  the  "  epoch-making  discov- 
ery "  of  Sir  Charles  Bell  and  Magendie.  The  sensory  fibres  en- 
ter the  spinal  cord  by  the  posterior  root,  the  motor  fibres  by  the 
anterior.  The  demonstration  of  this  fact  is  performed  by  dividing 
these  roots,  respectively,  and  observing  the  results.  When  a  pos- 
'  Pfliiger's  Arcliiv,  vii.,  pp.  632  ff.  ;  and  compare  Ibid.,  viii.,  pp   532  ff. 


124  PATHS    OF   ISTERVOUS   CONDUCTIOl^T. 

terior  i^oot  is  divided  all  the  structures  supplied  by  the  same  nerve 
lose  their  sensibility  ;  while  the  muscles  supplied  by  its  correspond- 
ing anterior  root  continue  to  be  thrown  into  action  by  the  will 
and  b}^  reflex  stimulation.  Moreover,  stimulation  of  the  central 
end  of  the  posterior  root  thus  divided  produces  sensory  effects,  but 
stimulation  of  its  peripheral  end  produces  no  motion.  When  an 
anterior  root  is  divided,  on  the  contrary,  the  muscles  supplied  by 
its  nerves  cannot  be  made  to  act  either  by  volition  or  by  reflex 
stimulation  ;  but  no  sensory  paralysis  is  produced.  Moreover, 
stimulation  of  the  peripheral  end  of  the  nerve  will  now  throw  the 
muscles  into  contraction,  but  stimulation  of  the  central  end  will 
produce  no  effects.  An  exception  to  the  exclusively  motor  effects 
of  the  peripheral  end  occurs  in  certain  cases  of  so-called  "recurrent 
sensibility;"  the  sensibility  shown  in  these  cases  is  probably  due 
to  the  fact  that  a  few  sensory  fibres  from  the  posterior  root,  after 
running  a  short  distance  in  the  mixed  nerve,  turn  back  and  run 
upward  in  the  anterior  root.  The  proof  is  then  complete,  so  far 
as  the  direct  motor  paths  to  the  striated  muscles,  and  the  specifi- 
cally sensory  paths  which  conduct  impulses  to  the  cerebral  hemi- 
si^heres,  are  concerned.  According  to  Sigmund  Mayer  '  it  does 
not  necessarily  follow,  however,  that  onhj  centripetal  impulses  are 
conducted  by  the  posterior,  and  only  centrifugal  by  the  anterior 
roots. 

§31.  The  general  aiTangement  of  the  motor  paths  in  that  part 
of  the  spinal  cord,  on  the  same  side,  where  they  enter  by  the  an- 
terior roots  of  the  nerves,  and  of  the  sensory  paths  in  the  posterior 
part  of  the  cord,  is  maintained  throughout.  In  man,  that  is  to 
say,  the  impulses  pass  up  or  down  the  cord  in  that  region  of  it 
at  which  they  leave,  or  by  which  they  enter  with,  the  anterior  or 
the  posterior  roots.  But  histology  shows  that  the  two  halves  of  the 
cord  are  anatomically  connected  by  the  commissures,  and  that  every 
part  of  each  half  is  bound  with  other  parts  of  the  same  half,  both 
up  and  down  and  to  and  fro.  Physiology,  too,  indicates  that  the 
paths  of  sensory  impulse  undei'go  a  partial  crossing  from  right  to 
left,  and  from  left  to  right.  For,  after  complete  section  of  one  lat- 
eral half  of  the  cord,  complete  loss  of  sensibility  of  either  side  in 
that  part  of  the  body  which  is  supplied  by  those  nerves  of  the  same 
side  that  enter  the  cord  below  the  place  of  section  does  not  re- 
sult. The  effects  that  do  result  depend  upon  the  animal  chosen 
for  experiment,  and  upon  the  height  at  which  the  section  is  made. 
Experiments  upon  the  lower  animals  seem  also  to  show  that  in 
their  case  a  partial  crossing  of  the  motor  paths  takes  place  in  the 
'  Hermann's  Handb   d.  Physiol.,  II.,  i.,  p.  217. 


PATHS   IN   THE   SPINAL   COLUMNS.  125 

spinal  cord  ;  the  evidence  from  pathology  makes  it  doubtful  whether 
in  man  any  crossing  from  side  to  side  occurs  in  the  voluntary 
motor  paths,  at  least  below  a  point  very  high  up  in  the  neck.  All 
the  evidence  shows  that  in  the  lateral  columns  both,  sensory  and 
motor  paths  are  to  be  found. 

§  32.  In  addition  to  the  general  statement  just  made,  experi- 
mental physiology  has  little  to  say  confirming  or  correcting  the  con- 
clusions of  histology  (see  p.  71  f.)  as  to  the  paths  of  neural  impulses 
in  the  spinal  cord  of  man.'  Experiments  which  attempt  to  make 
a  section,  either  of  all  the  fibres  in  the  anterior  columns,  leaving  all 
the  other  fibres  intact,  or  of  all  the  other  columns,  leaving  the  fibres 
in  the  anterior  columns  intact,  can  never,  indeed,  be  quite  sure  of 
their  success.  But,  on  the  whole,  their  resvilts  are  confirmatory  of 
the  statements  made  in  the  last  article.  Some  investigators  have 
endeavored  to  solve  the  same  problem  by  directly  stimulating  the 
fibres  of  the  different  columns  in  such  manner  as  to  confine,  as  far  as 
possible,  the  influence  of  the  excitatory  current  (or  other  stimulus) 
to  certain  definitely  selected  fibres,  and  so  to  exclude  all  reflex  ac- 
tion. It  is  found  that  no  reaction,  indicative  of  any  sensory  im- 
pulses whatever,  follows  the  stimulation  of  the  central  ends  of  the 
anterior  white  columns  of  the  spinal  cord  ;  but  stimulation  of  the 
peripheral  ends  of  these  same  columns  may  be  followed  by  muscu- 
lar contraction,  sometimes  (so  Longet  and  Kiirschner  found)  when 
mechanical  stimuli  are  used,  but  oftener  with  weak  electrical  cur- 
rents. .  Careful  cutting  of  these  columns  is  followed  by  no  signs  of 
pain. 

On  the  other  hand,  stimulation  of  the  central  cut  ends  of  the 
posterior  columns  produces  signs  of  pain,  and  other  sensory  effects ; 
for  this  pui-pose  Longet  has  used  electrical,  and  Eigenbrodt  and 
Schiff  mechanical  stimulation.  According  to  Schiff  and  others  the 
entire  cord  can  be  cut  through  from  before  back  to  the  posterior 
columns,  and  if  these  are  left  the  animal  will  retain  the  sense  of 
feeling.  As  to  a  further  differentiation  of  the  sensory  function  of 
these  columns,  different  experimenters  do  not  agree.  Some  would 
confine  their  function  to  impulses  that  give  rise  to  sensations  of 
touch,  on  the  ground  that  animals,  the  substance  of  whose  cord  has 
been  entirely  cut  through  with  the  exception  of  the  posterior  col- 
umns, retain  their  sensations  of  touch,  but  loose  their  susceptibil- 
ity to  pain  from  impressions  made  on  the  surfaces  whose  nerves 
enter  the  cord  below  the  place  of  section.     Impulses  which  give 

'  Comp.  the  generalizations  of  Eckliard  in  tlie  chapter  on  "  Verlauf  d.  mo- 
torischen  u.  seusiblen  Innervatiouswege  im  Riickenmarke,"  Hermann,  Handb. 
d.  Physiol.,  II.,  ii.,  pp.  148  ff. 


126  PATHS    OF   l^ERVOUS    CONDUCTION. 

rise  to  sensations  of  pain  must  therefore  pass  elsewhere  than  by 
the  posterior  strands  ;  that  is,  chiefly  by  the  gray  matter  of  the 
cord.  According  to  others,  however,  these  strands  conduct  sen- 
sory processes  only  in  so  far  as  they  serve  for  the  passage  through 
them  of  the  nerves  from  the  sensory  roots  ;  it  is,  then,  the  gray  sub- 
stance of  the  cord  which  conducts  these  processes  along  upward. 
In  addition  to  the  more  marked  sensory  effects  of  stimulating  the 
posterior  columns,  some  experimenters  get  effects  which  they  in- 
terpret as  showing  the  presence  of  motor,  and  even  of  voluntary- 
motor,  paths  in  these  columns.  Stilling,  for  example,  found  that 
voluntary  motions  occurred  after  one  entire  anterior  half  of  the 
cord  had  been  cut  through.  But  in  the  absence  of  proof  that 
no  motor  paths  in  the  lateral  columns  were  left  intact  by  his  ex- 
periments, and  in  view  of  the  fact  that  a  crossing  of  such  paths 
may  take  place  in  some  of  the  animals,  the  evidence  is  not  conclu- 
sive. Moreover,  Ttirck  and  others  have  found  that  the  posterior 
white  columns  may  be  entirely  cut  through  without  causing  motor 
disturbances. 

In  the  lateral  columns  of  the  cord,  paths  of  both  motor  and  sen- 
sory impulses  are  probably  to  be  found.  As  to  the  case  of  motor 
paths  there  is,  indeed,  no  reasonable  doubt — at  least  there  is  no  dis- 
pute. Ludwig  and  "Woroschiloff  found  that,  in  the  case  of  the  rab- 
bit, voluntary  movements  of  the  hinder  extremities  took  place  even 
after  section  of  the  anterior  and  posterior  strands,  and  of  the  gray 
matter  of  the  cord  in  the  cervical  region.  As  to  the  proofs  of  sen- 
sory paths  in  the  lateral  columns,  the  evidence  is  somewhat  con- 
flicting. Longet  and  Stilling  discovered  no  proof  of  their  existence  ; 
Schiff  pronounces  the  matter  doubtful ;  Tiirck  found  that  unmistak- 
able signs  of  pain  followed  the  cutting  of  these  portions  of  the  cord. 
Experiments  upon  animals  and  pathological  observation,  however, 
on  the  whole,  confirm  the  view  that  the  sensory  are  mixed  with  the 
motor  paths  in  the  lateral  columns.  As  Wundt '  expresses  the  ap- 
parent truth — in  the  side  strands  of  the  coi'd  a  part  of  the  system  of 
motor  fibres  is  shoved  off  toward  the  limits  of  the  posterior  columns 
and  surrounded  on  all  sides  by  branches  of  the  sensory  tract. 

It  must  be  borne  in  mind  that  the  function  of  neither  the  motor 
nor  the  sensory  tracts  is  such  that  a  nerve-commotion,  when  started 
in  one  of  the  columns,  must  necessarily  run  its  course  by  the  short- 
est path  in  that  one  column,  or  else  not  be  propagated  at  all  to  its 
destination.  Both  histology  and  physiological  experiment  indi- 
cate that  the  interlacing  of  the  nerve-fibres,  and  the  interruption  of 
theu'  course  with  nerve-cells,  provide  various  secondary  paths  in 
'Grundziige  d.  pliysiolog.  Psjchologie,  i.,  p.  101,     Leipzig,  1880. 


PATHS  IN"   THE   BRAIN.  127 

addition  to  that  which  may  be  called  the  primaiy  or  chief.  More- 
over, the  gray  substance  of  the  cord  not  only  distributes,  but  also 
carries  forward  the  nervous  impulses.  After  entire  half- section  of 
the  cord  the  sensory  tracts  of  the  other  half  still  seem  able,  in  a 
partially  substitutionary  way,  to  accomplish  the  work  normal  to 
both  sides.  And  even  in  the  case  of  the  voluntary  motor  tracts  in 
man's  spinal  cord,  though  such  a  work  of  substitution  does  not  take 
place,  we  cannot  affirm  that  the  paths  of  voluntary  innervation 
for  a  definite  set  of  muscles  are  invariably  the  same  through  their 
entire  length.  A  certain  latitude  of  movement  from  the  straight- 
forward course  of  the  impulse  undoubtedly  exists  even  in  such  a 
case. 

§  33.  Difficult  as  it  is  for  experimental  physiology  to  deal  with 
the  tracing  of  those  paths  along  which  the  sensory  and  motor 
impulses  flow  in  the  spinal  cord,  it  is  much  more  so  within  the 
nervous  mass  which  fills  the  cranial  cavity.  Both  the  structure  and 
the  functions  of  the  cerebrum,  as  a  group  of  chief  central  organs, 
make  it  nearly  impossible  experimentally  to  distinguish  between 
paths  of  voluntary  and  paths  of  merely  reflex  motion  ;  or  even  to 
conjecture  where,  within  its  substance,  impulses  that  have  been 
moving  along  some  more  clearly  defined  tract  may  not  divide  and, 
subdivide  indefinitely,  or — conversely — impulses  that  enter  along- 
several  converging  paths  be  concentrated,  as  it  were,  into  one  or  two 
that  are  more  definitely  fixed. 

The  evidence  by  which  histology  has  succeeded  in  tracing  cer- 
tain tracts  through  the  brain,  from  the  medulla  oblongata  to  the 
convolutions  of  the  cerebral  cortex,  has  been  presented  at  sufficient 
length  in  the  last  chapter  (see  pp.  76  f.,  87  f.,  and  97  f.).  The  fuller 
discussion  of  the  evidence  from  experimental  physiology  concerning 
the  same  subject  will  more  properly  appear  in  subsequent  chapters 
upon  the  automatic  and  reflex  functions  of  the  central  organs  and 
upon  the  localization  of  cerebral  function.  Certain  tracts  which  pass 
directly  from  the  crusta  through  the  internal  capsule,  without  en- 
tering the  basal  ganglia,  into  the  frontal  and  parietal  convolutions 
have  already  been  referred  to  as  probably  motor.  Others  which 
come  from  the  tegmentum,  enter  the  thalamus  and  subthalamic 
region,  and  emerge  after  being  redistributed  to  find  their  way  es- 
pecially to  the  tempero-sphenoidal  and  occipital  lobes,  have  been 
declared,  in  all  probability,  to  be  sensory.  With  this  statement, 
so  far  as  the  motor  tracts  are  concerned,  we  shall  see  that  the  con- 
ckisions  of  experimental  physiology  accord  very  well. 

§  34.  But  our  assured  knowledge  from  experiment  concerning  the 
paths  by  which  sensory  impulses  travel  in  the  brain  is  exceedingly 


128  PATHS   OF   NEEVOUS   CONDUCTIOlSr. 

meagre.  These  paths  are  probably  much  more  numerous  and  in- 
tricate than  those  along  which  the  motor  impulses  are  propagated. 
Moreover,  we  can  seldom  draw  conclusions  with  safety  conceriung 
the  sensations  of  the  lower  animals  ;  we  therefore  largely  lose  our 
help  fi'om  experiment  upon  them  to  determine  these  sensory  paths. 
The  phenomena  connected  with  all  sensory  disturbances  are  exceed- 
ingly complicated,  and  the  conclusions  they  seem  to  warrant  are 
often  conflicting.  For  example,  the  effect  of  destroying  a  sensory 
nerve-tract  in  the  head  does  not  consist  simply  in  the  destruction 
or  laming  of  some  one  definite  function.  On  the  contrary',  if  a 
sensory  cranial  nerve  is  severed,  the  various  different  functions  of 
feeling  pain,  of  pressure,  and  temperature,  and  the  power  of  localiz- 
ing, in  the  region  supplied  by  the  nerve  are  all  lost.  But  disease 
of  the  cerebro-spinal  axis  may  impair  one  or  more  of  these  func- 
tions, and  leave  the  others  intact,  in  a  given  region  of  the  periph- 
ery. Anaesthetics  also  may  obliterate  the  sense  of  pain  while  leav- 
ing that  of  contact  relatively  unimpaired. 

Still  more  difficult  of  comprehension  from  the  point  of  view  fur- 
nished by  the  general  physiology  of  the  nerves  are  the  degrees  of 
tenacity  with  which  different  sensory  functions,  even  when  adminis- 
tered by  the  same  sensory  nerve,  are  combined.  Loss  of  the  sense 
of  temperature  and  of  the  muscular  sense  rarely  or  never  occur 
separately  ;  but  muscular  sense  not  infrequently  disappears  and 
the  sensitiveness  of  the  skin  to  pressure  is  retained.  Upon  such 
phenomena  we  have  little  clear  light  to  throw.  It  can  simply  be  said 
that  the  distribution  of  the  sensory  nerves  within  the  centi'al  or- 
gans must  be  enormously  complicated,  and  that  we  have  absolute- 
ly no  knowledge  as  to  any  differences  in  the  kinds,  or  velocity,  or 
paths,  of  the  nerve-commotions  there,  that  will  help  us  to  account 
for  the  facts.  Yet  such  differences  in  the  sensations  doubtless  rest 
upon  differences  in  the  nerve-commotion  that  causes  them,  within 
that  inner  projection  system  of  sensory  impressions  which  is  fur- 
nished by  the  cortex  of  the  cerebrum. 

It  has  already  been  seen  that  the  paths  of  sensory  imjDulses  cross 
over  more  or  less  completely  within  the  spinal  cord.  They  also, 
like  the  paths  of  motor  impulses,  cross  in  the  region  where  the 
nerve-fibres  in  general  decussate — namely,  in  the  pons  varolii  and 
medulla  oblongata.  Experiment  and  pathology  both  show  that 
the  principal  paths  of  sensory  impulses  from  all  the  peripheral 
parts  of  the  trunk  of  the  body  and  from  its  mucous  membrane  lie 
close  to  those  of  the  motor  impulses  in  the  white  nervous  substance 
surrounding  the  basal  ganglia.  Effusions  of  blood  in  this  region 
not  only  cause  hemiplegia,  but  also  produce  more  or  less  impair- 


PATHS   IN   THE   BASAL   GANGLIA.  129 

ment  of  the  different  modifications  of  touch,  both  in  the  skin  and 
in  the  mucous  membrane.  According  to  some  authorities,  lesions 
in  the  same  region  often  so  impair  the  muscular  sense  that  the 
contraction  of  the  muscles  which  is  produced  by  electrical  stimula- 
tion is  no  longer  felt.  Veyssiere  and  others  suppose  that  injuries 
to  the  white  fibrous  matter  of  the  crura  cerebri,  the  internal  cap- 
sule, and  the  foot  of  the  corona  radiata,  invariably  produce  a  loss 
of  sensibility  on  one  side  of  the  body  ;  while  those  which  are  more 
definitely  confined  to  the  striate  body  have  this  effect  only  imper- 
fectly and  for  a  time — the  amount  of  the  effect  depending  upon  the 
amount  of  the  adjoining  white  substance  which  is  involved  in  the 
injury.  This  view,  like  many  others  on  the  general  subject,  is 
doubtful. 

§  35.  Attempts  have  been  made  to  localize  the  paths  of  sensory 
impulses  in  the  optic  thalami  and  those  of  motor  impulses  in  the 
striate  bodies  ;  and  in  connection  with  this  view  it  has  been  held 
that  the  former  are  chiefly  concerned  in  the  elaboration  of  sensory 
impulses  (as  sensory  ganglionic  centres),  and  the  latter  in  the 
elaboration  of  motor  impulses  (as  motor  centres).  This  theory  has 
been  wrought  out  (with  much  rhetoric  and  conjecture)  by  J. 
Luys.*  Luys  finds  in  the  optic  thalami  four  centres  which — lying- 
in  order,  one  behind  the  other  in  an  antero-posterior  line — conduct 
and  "  condense "  respectively  the  olfactory,  the  visual,  the  tact- 
ual, and  the  auditory  impressions  ;  the  corpora  striata  perform 
a  similar  ofiice  for  the  motor  impulses.  The  sensory  impressions 
which  come  from  the  periphery,  therefore,  all  run  through  the  op- 
tic thalami,  according  to  this  theory,  in  order  that  they  may  be 
"intellectualized"  (whatever  that  may  mean);  the  motor  through 
the  striate  bodies,  in  order  that  they  may  be  "materialized."  It 
is  enough  in  this  connection  to  say  that  no  such  comjjlete  dis- 
tinction of  function  in  the  basal  ganglia,  whether  as  conductors 
or  as  central  organs,  has  yet  been  made  out.  It  is  true,  however, 
that  the  paths  in  the  crusta  and  in  and  surrounding  the  striate 
bodies  are  probably  mainly  motor,  while  those  in  the  tegmentum 
and  in  and  around  the  optic  thalami  are  mainly  sensory.  The 
tendency  of  the  most  recent  investigation  is  toward  placing  more 
emphasis  upon  the  fibrous  nei-ve-matter  surrounding  these  organs 
as  furnishing  paths  for  the  conduction  of  both  kinds  of  impulses. 

^  Recherches  anatomiques,  physiologiques,  et  pathologiques  sur  les  Centres 
Nerveux,  1865  ;  and  The  Brain  and  its  Functions,  New  York,  1883. 
9 


CHAPTER  lY. 

AUTOMATIC   AND   KEFLEX   FUNCTIONS   OF   THE   CENTEAL 

OEGANS. 

§  1.  When  a  physiological  function  is  occasioned  in  a  peripheral 
nerve,  independently  of  a  so-called  act  of  will,  by  the  stimulation 
of  some  other  peripheral  nerve,  this  function  is  said  to  be  "  reflex." 
Such  a  reflex  function  of  the  nerve  is  regularly  brought  about,  how- 
ever, by  the  mediation  of  a  collection  of  ganglion-cells  and  inter- 
lacing nerve-fibres,  known  as  a  central  orgav.  In  other  words,  the 
secondary  stimulation  of  one  peripheral  nerve,  through  a  central 
organ,  as  a  result  of  a  primary  stimulation  of  some  other  periph- 
eral nerve,  is  a  reflex  action  of  the  nervous  elements.  The  entire 
cerebro-spinal  axis  is  a  pile  of  nervous  centres,  increasing,  on  the 
whole,  in  complexity  of  structure  and  of  function  from  below  up- 
ward, which,  with  the  nerve-tracts  running  into  and  out  of  it,  con- 
stitutes a  complicated  mechanism  capable  of  an  indefinite  variety 
of  such  reflex  functions.  But  the  spinal  cord  and  the  medulla 
oblongata  are  the  special  seat  of  many  such  functions.  On  the 
other  hand,  all  excitations  of  the  nervous  system  which  originate 
in  the  nervous  centres  themselves — that  is  as  distinguished  from 
being  called  out  there  by  the  nerve-commotion  brought  to  them 
through  the  afferent  nerves — are  called  "  automatic."  The  word 
automatic  must  doubtless  often  be  used  to  conceal  our  ignorance 
of  the  real  origin  of  a  neural  process.  And  doubtless,  also,  many 
processes  which,  on  first  inspection,  appear  to  be  automatic,  may 
be  discovered,  or  suspected,  to  be  in  reality  reflex.  But,  as  far  as 
our  information  goes  at  present,  not  only  movements  of  the  mus- 
cles through  the  stimulating  of  the  efferent  nerves  connected  with 
them,  but  also  the  inhibiting  of  such  movements,  and  the  rise  of 
sensations,  must  be  ascribed  to  the  automatic  action  of  the  central 
organs.  Changes  in  the  vital  conditions  to  which  these  organs  are 
subjected  by  their  immediate  surroundings,  and  especially  changes 
in  the  condition  of  the  blood  with  which  they  are  supplied,  ordina- 
rily constitute  the  internal  stimuli  to  which  they  respond  by  exer- 
cising their  peculiar  functions.  Automatic  activities  belong  dis- 
tinctively to  the  central  ganglia  of  the  brain  ;  it  is  more  difficult  to 


KINDS    OF   REFLEX   ACTIOIST.  131 

vindicate  tlieir  existence  in  the  spinal  cord.  In  general,  it  is  by  no 
means  easy  confidently  to  distinguish  between  the  purely  reflex 
and  the  purely  automatic  action  of  particular  central  organs.  The 
two  forms  of  action  are  doubtless  uniformly  blended  ;  so  that  what 
is  accomplished  by  any  central  organ  depends  both  upon  its  own 
internal  condition  and  molecular  activity  at  the  moment  when  the 
sensory  impulse  reaches  it,  and  also  upon  the  character  of  that  im- 
pulse. Inasmuch  as  it  is  a  vital  molecular  mechanism  connected 
by  an  indefinite  number  of  ties  with  other  similar  mechanisms,  the 
central  organ  constantly  acts  both  reflexly  and  automatically. 

§  2.  It  follows,  therefore,  that  several  kinds  of  reflex  action  are 
theoretically  supposable  in  the  nervous  system.  When  motor 
nerves  are  stimulated  in  a  secondary  way  through  a  central  organ, 
by  ajDjDlying  stimulus  to  the  sensory  nerve-endings,  the  effect  may 
be  called  reflex-motor.  If  an  excitation  of  a  motor  nerve  were 
transferred,  without  action  of  the  will,  to  one  or  more  sensory  paths, 
such  a  conversion  of  nervous  action  might  be  called  reflex-sensory. 
In  this  way  the  attemjDt  has  been  made  to  explain  the  feeling  of 
weariness  in  the  muscles  when  they  have  been  overexerted,  or  the 
feeling  which  we  describe  as  that  of  a  limb  being  "asleep."  It  has 
also  been  pi'oposed  to  speak  of  "co-motor  reflexes,"  in  cases  where 
two  motor  nerves  are  assumed  to  be  reciprocally  combined  in  their 
influence,  through  a  centi'al  organ;  or  of  "co-sensory,"  in  cases 
Avhere  the  same  relation  is  sustained  by  two  sensory  nerves.  As  an 
example  of  the  latter,  attention  has  been  called  to  the  sensation 
which  is  felt  in  the  nose  when  trying  to  look  at  the  sun.  Examples 
of  the  three  last  classes  of  alleged  reflex  functions  of  the  nervous 
system  are,  however,  for  the  most  part  very  doubtful ;  or  they 
admit  of  explanation  by  recognized  causes  in  another  way.'  It  is. 
only  concerning  the  laws  of  the  first  class  of  reflex  actions — the 
reflex-motor  or  sensory-motor — that  we  have  assured  scientific 
evidence.  The  reflex  function  of  a  central  organ  may  be  defined, 
then,  as  being  (at  least  in  its  simplest  form)  the  "  conversion  "  or 
"reflexion"  of  a  sensory  impulse  into  a  motor  excitation.  We 
must  guard  ourselves  carefully,  however,  against  the  misconception 
that  lurks  in  these  words :  the  eftect  of  the  central  organ  is  never 
that  of  merely  converting  or  reflecting  a  nerve-commotion  from  one 
perfectly  definite  sensory  path  to  an  equally  definite  motor  path. 
No  such  simple  figure  of  speech  will  serve  to  describe  its  function, 

§  3.  The  spinal  cord — complex  as  its  structure   and  functions 
are — is  much  the  simplest  and  most  accessible  for  experimental 
purposes  of  any  of  the  organs  of  the  cerebro- spinal  system  ;  it  is 
'  Comp.  Eckhard  in  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  pp.  33  tL 


132         THE  COED  AS  A  CENTRAL  ORGAN. 

pre-eminently  the  seat  of  unconscious  reflex-motor  functions.  It  is 
a  column  or  pile  of  centres,  bound  together  for  the  reception  of 
sensory  impulses  by  its  posterior  roots  and  for  redistributing  them, 
as  modified  by  its  own  molecular  structure  and  condition,  through 
the  efferent  fibres  of  the  anterior  roots.  Such  is  its  office  as  an 
organ  of  reflex  action  in  distinction  from  its  ofiice  as  an  organ  for 
conducting  neural  impulses.  We  consider,  then,  in  the  first  place, 
the  Sj)inal  Cord  as  a  Central  Organ. 

§  4.  As  the  "nerve-muscle  machine"  is  a  preparation  for  testing 
experimentally  the  laws  of  the  action  of  the  nerves  as  conductors, 
so  preparations  may  be  made  for  testing  the  laws  of  the  reflex  and 
automatic  functions  of  the  spinal  cord,  by  separating  that  organ 
from  the  brain  by  section  below  the  medulla  oblongata.  For  the 
purpose  of  experiment,  the  "brainless  frog  "  is  the  most  convenient 
of  such  preparations  and  the  most  fruitful  of  results.'  If  the  flank 
of  such  a  frog  be  lightly  touched,  the  resulting  reflex  motion  will 
be  limited  to  a  slight  twitching  of  the  muscles  that  lie  immediately 
beneath  the  spot  on  the  skin  thus  stimulated.  If  its  legs  be 
stretched  out  and  one  of  them  j)inched,  all  the  segments  of  the 
limb  thus  irritated  will  be  rapidly  flexed  in  the  definite  purposeful 
way  necessary  to  withdraw  it  from  the  irritation.  If  the  skin  of 
the  region  near  the  anal  orifice  be  pinched,  a  new  combination  of 
muscular  contractions  will  take  place  and  a  different  form  of  defen- 
sive movements  will  result :  the  feet  will  be  drawn  up  toward  the 
spot  irritated  and  the  legs  brusquely  extended,  as  though  to  push 
away  the  irritating  agent.  If  the  stimulus  applied  to  the  skin  of 
one  hind  leg  be  increased  by  forcibly  pinching  it,  the  resulting 
reflex  motions  may  involve  the  fore  leg  of  the  same  side,  then  the 
hind  leg  and  fore  leg  of  the  opposide  side,  and  finally  almost  all 
the  muscles  of  the  body.  Moreover,  changes  in  the  chai-acter  of 
these  reflex  motor  activities  take  place  which  are  plainly  adapted  to 
provide  for  changes  in  the  animal's  circumstances.  For  if  the 
right  flank  of  a  brainless  frog  be  irritated  with  a  drop  of  acid,  and 
at  the  same  time  the  right  leg  be  held  (the  member  which,  if  un- 
hindered, would  be,  almost  without  exception,  used  in  the  attempt 
to  remove  the  irritation),  or  the  right  foot  cut  off,  the  left  foot 
may  be  used  for  the  same  purpose  of  defence. 

.  Phenomena,  similar  to  those  obtained  in  the  case  of  the  frog, 
are  obtained  from  other  brainless  animals.  Thus  the  decapitated 
salamander,  when  the  skin  of  one  of  its  sides  is  pinched,  Avill  bend 
this  side  into  concave  shape  in  order  to  withdraw  it.    Not  succeed- 

'  For  detailed  information  see  Vulpian,  Le90iis  sur  la  Physiologic  du  Sys- 
tume  Nerveux,  pp.  311-465. 


REFLEXES   OF   THE   SPINAL   CORD.  133 

ing  in  this  way,  it  will  make  a  movement  with  its  foot  as  though  to 
push  away  the  cause  of  the  irritation.  In  the  case  of  the  higher 
animals  the  reflexes  of  the  spinal  cord  appear,  on  first  inspection, 
to  be  comparatively  feeble  and  lacking  in  purposeful  character. 
The  mammal,  for  a  relatively  long  time  after  the  division  of  the 
cord  from  the  brain,  exhibits  only  very  imperfect  reactions  in  parts 
of  the  body  supplied  by  nerves  which  spring  from  the  cord  below 
the  point  of  its  section.  But  if  the  animal  be  kept  alive  for  some 
time,  and  even  without  any  physiological  union  of  the  severed  jDarts, 
more  strong,  varied,  and  complex  movements  will  follow  upon  the 
stimulation  of  the  sensory  nerves  of  those  parts.  Immediately 
after  the  spinal  cord  of  a  dog  is  divided  low  down  in  the  dorsal 
region,  the  hind  limbs  hang  limp  and  motionless  ;  irritating  the 
skin  calls  forth  only  feeble  and  irregular  movements,  or  none  at  all. 
But  after  some  weeks  or  months  have  elapsed,  reactions  resembling 
those  already  described  in  the  case  of  the  frog  (taking  into  account, 
of  course,  the  difference  in  the  structure  and  normal  functions  of  the 
two  animals)  begin  to  appear.  The  hind  limbs,  instead  of  remain- 
ing motionless,  will,  when  the  animal  is  held  so  that  they  are  pen- 
dent, be  drawn  up  and  let  down  again  with  a  kind  of  regular  rhythm, 
as  a  result  of  the  constant  stimulation  of  their  motor  nerves  by  the 
sensory  nerves,  through  the  spinal  cord.  Moreover,  it  is  found  that 
the  breed,  age,  sex,  and  training  of  the  animal  determine  the  charac- 
ter of  these  brainless  reflex  movements.  That  is  to  say,  the  spinal 
cord,  as  a  nervous  mechanism,  embodies  in  its  very  structure  and 
functions  all  the  peculiarities  due  to  these  causes.  And  when  its 
activities  are  elicited  through  the  stimulus  which,  arising  in  many 
various  regions,  flows  in  upon  it  along  the  sensory  nerve-tracts,  or 
through  some  stronger  but  limited  impulse  occasioned  by  the  a]>- 
plication  of  stimulus  to  a  particular  spot  on  the  skin  with  a  definite 
degree  of  energy,  these  activities  bear  the  character  both  of  the 
stimulation  and  of  the  mediating  central  organ. 

§  5.  Little  need  be  added  to  what  has  already  been  said  (Chap. 
n.,  §  9),  in  description  of  that  mechanism  of  the  cord  to  which 
the  foregoing  remarkable  functions  are  referred.  Earlier  investi- 
gators '  assumed  the  existence  of  a  special  sj'stem  of  sensory  and 
motor  nerve-fibres,  with  connecting  nerve-cells,  designed  and  apjjro- 
priated  solely  for  executing  these  reflex-motor  activities.  That  the 
motor  tracts  for  reflex  movements  are  to  a  certain  extent  distinct 
in  the  spinal  cord  from  those  devoted  to  sj)ecifically  voluntaiy  ac- 
tivities, there  seems  to  be  good  reason  for  affirming  ;  but  the  older 

'  For  example,  Marshall  Hall,  in  liis  New  Memoir  on  tlie  Nervous  System. 
London,  1848. 


134        THE  CORD  AS  A  CENTEAL  ORGAN. 

supposition,  that  there  are  double  tracts, — one  connected  with  con- 
scious and  voluntary  reaction  upon  sensation,  and  one  connected 
with  unconscious  and  involuntary,  or  merely  reflex-motor,  reac- 
tion,— between  the  spinal  cord  and  the  end-organs  of  sensation 
and  motion,  is  almost  certainly  incorrect.  It  seems  antecedently 
very  improbable  that  every  spot  of  the  skin  should  be  equij)ped 
with  such  a  twofold  outfit  of  both  kinds  of  nerve-fibres.  No  par- 
ticular nerves  which  serve  merely  for  reflex-motor  functions,  and 
which  have  no  connection  either  with  conscious  sensation  or  with 
voluntary  motion,  can  be  pointed  out. 

"What  happens  with  respect  to  conscious  sensation — the  rise  of 
it  or  its  failure  to  rise — depends  rather  upon  the  effect  of  the 
stimulus  on  the  end-organ,  and  upon  the  condition  in  which  that 
stimulus  finds  the  central  organ  on  its  arrival  there.  In  consider- 
ing that  mechanism  of  the  spinal  cord  which  comes  into  use  when 
it  acts  as  a  central  organ  in  all  the  reflex-motor  activities  belonging 
to  it,  the  ofl&ce  of  the  ganglion-cells  is  usually  made  prominent. 
And  it  can  be  definitely  proved  that  these  cells  are  an  important 
part  of  the  reflex  mechanism  of  the  cord.  But  the  extremely  del- 
icate network  of  interlacing  nerve-fibres  in  which  the  processes 
of  these  cells  lose  themselves  also  bears  an  important  part  in  the 
same  functions.  Precisely  what  elements  of  the  central  substance 
alone  act,  and  precisely  how  the  elements  act  that  do  act,  it  is  im- 
possible to  say. 

§  6.  The  following  laws  embody  the  most  important  general  re- 
sults of  experiment  upon  the  reflex-motor  functions  of  the  spinal 
cord,  as  applied  to  a  variety  of  animals  under  a  great  number  of 
chan":ing  conditions  and  circumstances. 

The  primary  stimulation  of  the  sensory  nerves  must  have  a  cer- 
tain degree  of  strength  and  suddenness  in  order  to  produce  a  sec- 
ondary excitation  of  the  motor  nerves  through  the  centres  of  the 
spinal  cord.  This  is  true  of  all  the  different  kinds  of  stimuli  by 
application  of  which  spinal  reflexes  can  be  obtained..  Continuous 
irritation  of  the  skin,  if  very  slowly  increased,  may  be  carried  to 
the  extent  necessary  to  destroy  its  sensitive  surface,  without  giving 
rise  to  any  reflex  movements  ;  but  a  less  degree  of  stimulus,  if 
suddenly  applied,  will  call  forth  such  movements.  Different  chem- 
ical substances,  when  used  as  irritants,  j)roduce  effects  dependent 
upon  the  strength  of  the  solution.  Thus  a  weak  solution  {\-\  fo) 
of  sulphuric  acid  is  recommended  by  some  exj^erimenters  ;  and 
it  is  asserted  that  in  this  way  exactly  the  same  reflex  move- 
ments, as  respects  kind  and  degree,  can  be  repeatedly  got  from  the 
same  nerve-preparation,  with  a  machine-like  regularity.    Each  chem- 


SPEED   OF   REFLEX   PROCESSES.  135 

ical  stimulus  lias  its  lower  limit  of  concentration  which  will  produce 
any  reflex  movement,  and  also  its  latent  period.  The  time  of  the 
latent  period  for  weak  solutions  of  sulphuric  acid  is  said  by  Baxt ' 
to  increase  nearly  in  geometrical  ratio,  while  the  concentration  of 
the  acid  diminishes  in  ai'ithmetical  ratio.  The  chemical  stimulus, 
like  the  mechanical,  can  be  so  slowly  increased  in  strength  as  to 
produce  no  effect.  The  same  thing  is  also  true  of  thermic  stimu- 
lus. A  decapitated  frog  may  be  placed  in  water,  and  the  water 
gradually  heated  to  the  point  at  which  heat- rigidity  sets  in,  without 
showing  any  reflex  activity.  This  fact,  however,  may  be  in  part 
ascribed  to  the  direct  effect  of  the  heat,  diffused  from  the  skin 
upon  the  central  organ.  The  same  law  which  renders  stimulus 
inoperative,  when  very  gradually  increasing  in  strength,  applies  to 
the  use  of  the  electrical  current.  Repetition  of  the  shocks  is  much 
more  effective  than  a  slow  increase  in  the  strength  of  the  current. 
Single  induction-currents  are  relatively  powerless,  and  produce  no 
effect  unless  they  have  a  high  degree  of  strength.  Frequent  inter- 
ruptions greatly  increase  the  efficiency'  of  the  constant  current  in 
producing  reflex  movements.  It  Avould  seem,  then,  that  a  kind  of 
summation  of  afferent  impulses  may  take  place  in  the  spinal  cord  ; 
that  is  to  say,  the  repeated  excitation  of  the  nervous  centre  starts 
a  nerve-commotion  in  its  substance,  which  gathers  intensity  until 
it  breaks  over,  as  it  were,  into  the  adjoining  motor  tracts.  We  can 
scarcely  affirm,  however,  that  such  summation  of  many  impulses  is 
necessary  to  start  off  the  nervous  centre,  as  it  were,  since  the  sin- 
gle making  of  the  constant  current,  or  a  single  strong  induction- 
shock,  may  be  followed  by  a  number  of  reflex  movements. 

§  7.  The  speed  of  reflex  processes  is  apparently  increased  by 
increasing  the  strength  of  the  stimulus.  We  have  already  spoken 
(p.  123)  of  the  delay  which  the  process  of  conduction  suffers  in  the 
spinal  cord  when  passing  longitudinally.  The  time  of  cross-con- 
duction also  in  the  cord  seems  to  be  a  function  of  the  strength  of 
the  stimulus,  Exner  °  calculated  by  an  experiment,  which  con- 
sisted in  causing  one  eyelid  to  move  by  stimulating  the  other,  that 
the  time  consumed  in  the  specifically  central  operations  of  the  re- 
flex act  can  be  made  to  vary  between  0.055  and  0.047  of  a  second 
by  increasing  the  strength  of  the  stimulus.  Rosenthal  ^  and  others 
have  found  that  the  time  for  any  reflex  act  diminishes  cousiderabl}'^ 
with  the  increase  of  the  strength  of  the  stimulus  ;  is  greater  in  trans- 
verse than  in  longitudinal  conduction  ;  and  is  much  increased  by  ex- 

'  Quoted  in  Hermann,  Handb.  d.  Physiol.,  II.,  ii.,  p.  29. 

^  See  Pflliger's  Archiv,  viii.,  p.  530  ff. 

3 Mooatsbericlit  d.  Berlin.  Acad.,  1873,  p.  104. 


138  THE   COED   AS   A   CENTEAL   OEGAI<r. 

haustion  of  the  cord.  With  veiy  strong  stimuli  it  becomes  almost 
too  brief  for  observation.  Wundt, '  however,  denies  that  the  time  of 
the  reflex  act  is  dependent  upon  the  strength  of  the  stimulus  ;  on  the 
contrary,  he  affirms  that  the  time  is  either  very  little  or  none  at  all 
affected  by  changes  in  strength  of  the  stimulus,  or  else  is  even 
changed  in  the  contrary  direction  to  that  required  by  the  alleged 
law  of  Exner  and  Rosenthal. 

§  8.  The  condUion  of  the  sjyinal  cord,  at  the  time  when  it  re- 
ceives the  impulses  of  the  sensory  nerves,  undoubtedly  determines 
to  a  large  extent  the  character  of  the  resulting  reflex  motions. 
Lesion  increases  the  excitability  of  the  part  below  the  lesion,  and 
this — for  example,  in  the  case  of  reflex  movements  of  the  posterior 
limbs — according  to  the  amount  of  the  cord  removed  from  the  por- 
tion of  it  lying  anterior  to  its  nervous  connections  with  these  limbs.^ 
Marked  effects  are  also  produced  by  certain  drugs,  as  strychnine, 
chloroform,  aconite,  quinine,  etc.  Of  these  drugs,  some  heighten 
and  some  depress  its  excitability.  In  an  animal  slightly  poisoned 
with  strychnine,  the  excitability  of  the  cord  is  more  or  less  height- 
ened ;  and  in  cases  of  strong  poisoning  with  the  same  drug,  the 
least  stimulation  may  call  forth  a  condition  of  tetanus  or  convul- 
sive cramping  extending  to  the  whole  body.  Two  ways  of  exjDlain- 
ing'  this  effect  upon  the  mechanism  of  the  central  organ  are  pos- 
sible :  one,  that  the  excitability  of  those  portions  of  this  organ 
which  mediate  between  the  sensory  and  motor  impulses  is  so  much 
increased  by  the  poison  that,  on  being  stimulated,  they  explode 
their  molecular  energy,  as  it  were,  and  cause  it  to  be  diffused  with 
great  strength  into  unaccustomed  paths  ;  the  other,  that  the  effect 
of  the  poison  is  to  diminish  the  resistance  along  all  the  network 
of  paths,  both  habitual  and  unaccustomed,  in  the  spinal  cord. 
Between  these  two  explanations  Eckhard  ^  Avill  not  decide  ;  Rosen- 
thal seems  to  prefer  the  former,  Foster'  and  others  the  latter. 
Chloroform  and  various  other  anaesthetics  diminish  the  reflex  ac- 
tion of  the  cord.  As  to  the  effect  of  changes  in  temperature,  and 
in  electrical  condition,  upon  the  spinal  reflexes,  the  conclusions  of 
different  experimenters  are  somewhat  divergent.  This  power  of 
the  nervous  mechanism  is,  as  we  have  already  seen,  retained  longer 
in  low  than  in  high  temperatures.  According  to  Cayrade,  Avhen 
the  temperature  of  the  whole  cord  is  raised,  the  reflex  movements, 
however   produced,  become  more    energetic  and  the  single  con- 

1  Mechanik  d.  Nerven,  abth.  ii.,  pp.  14  ff.     Stuttgart,  1876. 

"  Vulpian,  Leyoiis,  etc.,  p.  438. 

•'In  Hermann,  Haudb.  d.  Physiol.,  II..  ii.,  p.  42. 

*  Text-book  of  Plijsiologj,  p.  602. 


THE  EFFECT  OF  LOCALITY.  187 

tractions  last  longer.  Another  observer  found  a  temporary  rise  of 
excitability,  followed  by  a  depression,  on  beating  sections  of  the 
cord  between  75°  and  158°  Fabr.  On  the  other  hand,  some  observ- 
ers are  of  the  opinion  that  cold  increases  the  excitability  of  the 
cord.  In  experimenting  with  the  electrical  current  it  is  very  diffi- 
cult to  distinguish  between  its  effect  upon  the  central  organ  as  the 
mediating  mechanism  and  the  effect  of  the  same  stimulus  upon 
the  nerve-roots  and  nerve-paths  between  which  the  mediation 
occurs. 

§  9.  The  locality  to  which  the  stimulus  is  applied  has  a  marked 
influence  in  determining  the  extent  and  character  of  the  resulting 
reflex  movements.  The  most  important  difference  of  aU  is  that 
found  by  stimulating  some  spot  of  the  skin,  and  then  comparing 
the  resulting  reflex  action  with  what  follows  upon  the  application 
of  the  same  stimulus  to  the  trunk  of  the  nerve  which  is  distributed 
to  that  region  of  the  skin.  The  simple  nervous  impulses,  which 
result  from  stimidating  the  afferent  nerve-fibres  directly,  call  forth 
irregular  spasms  in  a  few  muscles  only ;  the  complicated  nervous 
impulses,  which  result  from  applying  the  same  stimulus  to  the 
skin,  are  followed  by  extended  movement  of  many  muscles  directed 
toward  definite  ends.  Moreover,  it  is  much  more  easy  to  produce 
reflex  action  by  a  shght  pressure  on  the  skin  than  by  even  strong 
induction-shocks  when  applied  to  the  nerve-trunk.  By  separating 
a  small  bit  of  skin  from  that  surrounding  it  on  the  back  of  a  brain- 
less frog,  while  taking  care  not  to  injure  the  nerves  that  attach  it 
to  the  body,  the  foregoing  difference  may  be  made  strikingly  clear 
in  an  experimental  way.'  What  particular  reflex  actions  will 
be  evoked  by  the  stimulus  is,  in  each  case,  dependent  ujDon  the 
particular  locahty  of  the  skin  to  which  the  stimulus  is  applied. 
Such  facts  suggest  the  truth  that  the  entu-e  mechanism  of  the  cord 
is  broken  up  into  centres  of  activity,  which,  however,  are  in  close 
molecular  relation  with  each  other,  and  which  are  of  a  somewhat 
expansive  nature. 

In  view  of  the  foregoing  truths  Pfliiger"  has  formulated  the  fol- 
lowing laws  of  relation  between  the  stimulation  and  the  resulting 
reflex  action  :  {a)  In  the  case  of  a  spinal  cord  from  which  the 
medulla  oblongata  is  wholly  severed,  all  reflex  motion  confined  to 
one  side  of  the  body  is  due  to  stimulation  of  that  side,  (b)  Reflex 
movements  of  both  sides  never  occur  in  a  diagonal  direction  ;  that 
is  to  say,  stimulating  one  hind  limb  can  never  evoke  reflex  move- 

'  See  the  article  of  Fick  and  Erlenmeyer  m  Pfliiger's  Archiv,  iii.,  p.  326. 
'^  In  his  work,  Ueber  d.  sensorischen  Functionen  d.  Riickenmarks.     Berlin. 
1853. 


138  THE   COKD   AS   A   CENTKAL   ORGAN". 

merit  of  that  limb  and  of  the  fore  Hmb  of  the  opposite  side. '  (c)  If 
reflex  action  is  called  out  in  the  limbs  of  both  sides,  and  such  action 
is  stronger  on  one  side  than  on  the  other,  then  it  is  stronger  on  the 
side  stimulated,  (d)  If  the  motor  effects  of  the  stimulation  show 
that  the  excitation  has  been  "irradiated,"  as  it  were,  from  one 
centre  to  another,  then  such  movement  of  irradiation  is  always 
downward  toward  the  medvdla  oblongata  in  the  brain,  and  upward 
in  the  cord  toward  the  same  organ.  It  is  by  no  means  certain, 
however,  that  these  formulas  (especially  the  second — No.  b)  admit 
of  no  exceptions  which  are  involved  in  the  peculiar  structure  and 
functions  of  the  cords  of  certain  animals.  But  the  general  rule 
appears  to  be,  that  the  excitation  of  a  sensory  nerve  witli  a  slight 
degree  of  stimulus  gives  rise  to  reflex  movements  which  originate 
in  the  cord  on  the  same  side,  at  about  the  same  altitude  as  that  at 
which  the  sensory  imjDulses  enter  the  cord  ;  with  an  increased  amount 
of  stimulus,  it  gives  rise  to  those  also  that  arise  in  the  other  half  of 
the  cord  at  the  same  altitude ;  with  a  stiU  greater  amount,  to  those 
which  arise  above  and  below  on  both  sides  of  the  cord,  with  the 
preference  given  to  the  same  side.  That  is,  the  molecular  disturb- 
ance, as  it  is  dispersed  or  radiated,  passes  from  the  cells  and  net- 
work of  fibres  situated  near  together  on  the  same  side  of  the  cord, 
first  to  those  on  the  other  side  of  the  cord  at  the  same  altitude,  and 
then  diffuses  itself  on  both  sides  up  and  down  the  cord."  Accord- 
ingly, it  is  only  after  allowing  for  a  difference  in  the  obstacles  to  be 
overcome  along  the  different  paths  anatomically  open  to  any  nerve- 
commotion  in  the  spinal  cord,  that  we  can  adopt  the  declaration 
of  Luchsinger :  ^  When  an  excitation  is  started  anywhere  in  the 
spinal  cord,  it  radiates  from  this  point  in  all  directions,  but  with 
diminishing  intensity.  Hence  the  title  Avhich  Flourens  and  Vul- 
pian,^  following  him,  have  given  to  the  spinal  cord — "the  organ  for 
the  dispersion  of  irritations." 

§  10.  Besides  such  undoubted  reflex  action  as  the  foregoing, 
other  cases  where  the  spinal  cord  controls  the  muscles  of  the  body 
are  less  certainly  of  a  purely  reflex  character.  Indeed,  for  some 
such  cases  the  title  of  "  automatic  "  has  been  employed.  The  cord 
is  not  capable  of  "  irregular  automatism  " — that  is,  of  spontaneous 
excitation  like  that  which  takes  place  in  the  higher  nervous  centres 

'  See  the  observations  of  Luchsinger,  which  seem  to  show  that  in  some  ani- 
mals— as,  e.g.,  the  salamander,  turtle,  and  even  dogs,  when  under  the  inttu 
ence  of  ether — cross  reflexes  in  violation  of  Pflliger's  law  do  sometimes  occur 
Pflijger's  Archiv,  xxii.,  pp.  179  fE. 

'^  Compare  Wundt,  Grundzijge  d.  physiol.  Psychologie,  i.,  pp.  103  and  109. 

^  Pflliger's  Archiv,  xxii.,  p.  178. 

^  Lec^ous  sur  la  Physiologie,  etc. ,  p.  404. 


TONIC  ACTION   OF   THE   CORD.  139 

on  volition.  If  a  brainless  frog,  for  example,  be  kept  in  a  condi- 
tion of  perfect  equilibrium  with  respect  to  stimulus,  it  will  remain 
wholly  motionless.  But  the  cord  of  such  an  animal  will  continue 
to  influence  certain  muscles  of  the  body  through  the  motor  nerves, 
even  in  cases  where  sensory  impulses  are  diflficult  or  impossible  to 
trace.  What  is  called  the  '•  tonic  action "  of  the  cord  upon  the 
skeletal  and  sphincter  muscles,  or  the  smooth  muscles  of  the  ar- 
teries, is  a  chief  illustration  of  this  influence.  The  fact  that  such 
tonic  action  does  not  contract  all  the  muscles  connected  with  the 
cord  at  the  same  time,  or  any  one  set  of  them  with  the  same  en- 
ergy as  any  other,  throws  some  suspicion  on  its  alleged  automatic 
character.  A  careful  sifting  of  the  evidence  rather  induces  us  to 
ascribe  this  influence  to  the  constant  reflex  action  of  stimulus  from 
subtle  changes  in  the  external  circumstances  in  which  the  animal 
is  placed.  Moreover,  the  sensory  nerves  in  the  muscles  and  ten- 
dons, as  well  as  in  the  skin  and  organs  of  special  sense,  may  occa- 
sion the  rise  and  continuance  of  such  reflex  action.  Different  in- 
vestigators, almost  without  exception,  have  failed  to  notice  any 
lengthening  of  a  muscle  (or  loss  of  its  tone)  when  the  nerve  going 
to  it  is  severed  from  the  cord.  That  this  so-called  "tonic"  influ- 
ence is  largely  reflex-motor  is  also  shown  by  the  fact  that  the  tone  of 
the  muscles  is  lost  when  the  skin  covering  them  is  removed,  or  when 
the  posterior  root  which  furnishes  sensory  impulses  for  the  motor 
nerves  connected  with  them  is  cut,  Brondgeest  has  shown  that, 
when  a  decapitated  frog  is  hung  up  after  having  the  sciatic  plexus 
cut  on  one  side,  the  leg  is  more  flexed  (that  is,  the  muscles  have 
more  of  tone)  on  the  other  side.  But  the  same  flaccid  condition  of 
the  muscles  can  be  produced  by  cutting  only  the  posterior  (or  sen- 
sory) roots  of  this  plexus.  This  observer  is  satisfied  that  the  con- 
traction of. the  muscles  in  the  uninjured  limb  is  due  to  stimulation 
from  the  nerves  of  the  skin  ;  the  tonic  action  of  the  cord  on  the 
skeletal  muscles  is,  therefore,  reflex.  The  only  objection  to  consid- 
ering the  tone  of  the  sphincter  muscles  reflex  lies  in  the  fact  that  this 
tone  continues  to  exist  after  all  other  reflex-motor  action  has  been 
suppressed  by  narcotics  ;  but  our  knowledge  of  the  nervous  mechan- 
ism wliich  conti'ols  these  muscles  is  not  sufficiently  complete  to  make 
it  certain  that  we  have  excluded  all  possible  forms  of  reflex  influence. 
Of  the  marked  influence  of  the  nervous  system  upon  the  cali- 
bre of  the  arteries,  and  through  this  upon  the  character  of  the 
circulation  of  the  blood,  there  is  abundant  evidence.  Besides  the 
main  vaso-motor  centres  in  the  medulla  oblongata,  certain  parts  of 
the  spinal  cord  are  caj^able  of  actiug  as  such  centres.  Circulation 
may  continue  with  regularity  in  a  beheaded  frog  ;  but  the  removal 


140  THE   CORD   AS   A   CENTEAL   OEGAIST. 

also  of  any  considerable  part  of  tlie  cord  affects  the  circulation 
tkrough  the  loss  of  tone  in  the  blood-vessels  which  it  occasions. 
The  mechanisms  for  expanding  and  contracting  the  arteries  are 
apparently  interlaced  with  those  for  contracting  the  skeletal  mus- 
cles, in  all  portions  of  the  cord.  But  their  chief  work  undoubt- 
edly consists  in  transforming  afferent  impulses  into  efferent  vaso- 
motor impulses  directed  toward  the  dilatation  or  constriction  of  the 
arteries.  Whether  they  are  capable  of  automatic  action — in  the 
sense  in  which  the  medulla  oblongata  seems  to  be  thus  capable — 
is  a  question  we  need  not  discuss  in  detail  here. 

§  11.  The  facts  already  alluded  to,  and  others  similar,  form  the 
basis  for  the  assumption  of  "  Centres  "  in  the  spinal  cord.  In  general, 
the  application  of  a  given  amount  of  stimulus  to  a  definite  group  of 
sensory  nerves  calls  forth  reflex-motor  activities  in  definite  groups 
of  muscles  by  means  of  a  certain  region  of  the  cord.  What  groups 
of  muscles  are  thus  moved  depends  upon  the  amount  of  the  stimu- 
lus and  the  locality  of  its  application.  This  fact  is  due  to  disper- 
sion of  that  nerve-commotion  which  is  set  up  at  different  points 
in  the  course  of  the  cord  by  the  excitation  of  those  points  through 
the  sensory  nerves.  That  is  to  say,  the  mechanism  of  this  central 
organ  is  so  constructed  as  to  connect  the  sensory  with  the  motor 
tracts,  more  favorably  in  some  regions  than  in  others.  Such  re- 
gions are  the  so-called  reflex  centres  of  the  spinal  cord.  If,  how- 
ever, a  more  or  less  constant  flow  of  motor  impulses  takes  place 
from  any  region,  and  this  flow  is  due  to  molecular  activity  not 
occasioned  by  the  sensory  nerve-fibres  of  the  region,  then  such 
region  may  also  be  called  an  automatic  centre.  Nothing  would 
seem  to  prevent  the  same  region  from  acting  as  both  a  reflex  and 
an  automatic  centre.  The  general  principle  may  then  be  formulated 
as  follows  :  "  The  spinal  cord  is  the  proximate  centre,  the  proximate 
physiological  hearth  of  excitation,  for  all  the  nerves  that  originate 
from  it."  This  principle  has  been  defended  and  illustrated  with  many 
researches  by  Legallois,  Volkmann,  Pfliiger,  Goltz,  Luchsinger,  and 
others.  In  accordance  with  it,  and  especially  since  the  "epoch- 
making  "  experiments  of  Goltz  upon  the  spinal  cord  of  dogs,  many 
functions  which  were  formerly  ascribed  to  the  brain  have  been 
shown  to  have  their  proximate  centre  in  the  spinal-cord.  In  ac- 
cordance with  the  same  principle,  it  is  discovered  that  different 
animals  have  different  spinal  centres  varying  in  relation  to  their 
peripheral  structure  and  their  habits.' 

'  Compare  the  results  of  the  researches  of  LangendorfF  in  the  Archiv  f. 
Anat.  u.  Physiol.,  Physiolog.  Abth.,  1880,  pp.  518  ff.,  and  1881,  pp.  519  ff.; 
aud  of  Luclisiuger  iu  Plluger's  Archiv,  xxii.,  pp.  158  fE.,  and  xxiii.,  pp.  308  fE. 


CEISTTKES    IlSr   THE    SPIISTAL    COED.  141 

In  illustration  of  the  last  point  the  following  facts  may  be  men- 
tioned  :  By  the  sufficiently  long-continued  and  strong  stimulation 
of  any  portion  of  the  skin  of  a  decapitated  frog,  reflex  movements 
may  be  induced  in  all  of  its  muscles.  With  rabbits,  however,  a  reflex 
action  of  one  hind  leg  can  be  caused  by  stimulating  the  sensory 
nerves  of  a  fore  leg,  only  in  case  a  portion  of  the  medulla  oblon- 
gata (at  least  about  one-third)  be  left  attached  to  the  cord.  With 
the  cord  alone,  the  stimulation  of  one  hind  leg  fails  to  excite  ac- 
tion in  either  of  the  fore  limbs.  By  using  great  care  and  artificial 
respii'ation,  Luchsinger '  succeeded  in  obtaining  what  he  calls  a 
"  trotting  reflex  "  from  the  spinal  cord — after  being  completely  sev- 
ered from  the  medulla  oblongata — of  several  young  animals  with 
which  that  form  of  movement  is  natural.  Thus  the  diagonal  op- 
posite extremities  of  goats  and  cats  were  moved  in  response  to 
even  such  weak  stimulation  as  passive  motion  of  the  fore  leg,  gen- 
tle pressui'e,  and  weak  electrical  currents.  In  general,  then,  it 
would  seem  that  the  spinal  cord  of  every  animal  is  a  series  of  con- 
nected mechanisms,  which  are  arranged  so  as  to  move  the  muscles 
of  the  body,  either  under  the  control  of  the  higher  nervous  centres 
or  in  response  to  stimulation  entering  it  at  any  point  through  the 
sensory  peripheral  nerves,  in  accordance  with  the  specific  structure 
and  habits  of  the  animal. 

Many  of  the  chief  special  centres  connected  with  the  organic  and 
vital  functions  are  located  in  the  medulla  oblongata ;  those  con- 
nected with  the  co-ordination  of  impressions  of  the  special  senses 
and  muscular  action  belong  to  the  still  superior  portions  of  the 
cerebro-spinal  system.  But  the  spinal  cord  also  contains  mechan- 
isms which  serve  as  centres  of  both  these  kinds."  Their  location, 
however,  is  so  much  a  matter  of  the  special  physiology  of  particular 
species  of  animals,  and  is  so  indirectly  connected  with  the  inquiries 
of  physiological  psychology,  that  it  is  unnecessary  to  add  anything 
further  upon  the  subject. 

§  12.  The  question  whether  the  spinal  cord  is  excitable  as  a 
whole,  and  in  its  several  parts,  by  artificial  stimulation,  has  been 
much  debated.      Its  direct  excitability  as  a  whole  is  denied  by 

'  See  Pflliger's  Arcliiv,  xxviii. ,  pp.  65  ff. 

^  Besides  the  vaso-motor  centres  already  referred  to,  those  for  micturition, 
defecation,  erection,  parturition,  etc.,  may  also  be  mentioned.  Goltz,  ui  his 
celebrated  researches  in  1874  (see  Pfluger's  Archiv,  viii.,  pp.  474  ff. ),  showed 
that  normal  micturition  may  take  place  in  a  dog  in  which  the  lumbar  region 
has  been  completely  severed  from  the  dorsal  region.  The  influence  of  the 
cerebral  centres  seems,  however,  to  be  necessary  to  cause  a  steady  increase  or 
decrease  of  the  action  of  the  sphincter  ani.  The  cilio-spinal  centre,  located  by 
Budge  at  the  seventh  and  eighth  cervical  rootSi  is  more  doubtful. 


142  EXCITABILITY    OF   THE   CORD. 

SeLiff, '  who  declares  that  the  motions  obtained  by  stimulating  any 
part  of  the  cord  with  electricity  comprise  only  those  muscles  which 
are  j)hysiologically  related,  to  the  exclusion  of  those  which  are  ana- 
tomically contiguous  through  the  stimulated  part  of  the  cord.  A 
strong  local  stimulus,  he  affirms,  produces  just  the  same  reflex  mo- 
tions as  those  which  are  accustomed  to  arise  on  occasion  of  an  ex- 
tended irritation  of  the  skin  at  the  places  to  which  the  nerves  is- 
suing from  this  locality  of  the  cord  are  distributed.  It  is  inferred, 
then,  that  the  resulting  motions  are  obtained  only  reflexly,  by  in- 
volving the  sensory  nerve-roots.  Bat  that  certain  longitudinal  parts 
of  the  cord  can  be  directly  stimulated  seems  capable  of  demonstra- 
tion. For  Fick  and  Engelken'^  found  that  movements  of  the  mus- 
cles were  obtained  when  the  anterior  columns  were  isolated  from 
the  rest  of  the  cord  for  a  considerable  distance  and  then  stimulated. 
Lucbsinger's'  experiments,  moreover,  contradict  the  conclusions  of 
Schiff;  and  Mendelssohn"  found  that  the  reaction-time  of  the  an- 
terior half,  and  especially  of  the  anterior  columns  of  the  cord,  was 
uniformly  less  than  the  reaction-time  of  its  posterior  columns.  The 
latter  also  found  that  weaker  stimuli  would  suffice  to  excite  motion 
when  applied  to  the  anterior  columns.  But,  according  to  Schiff  ^ 
again,  the  cord  contains  no  motor  elements  that  are  directly  exci- 
table except  the  central  paths  of  the  nerve-roots.  He  also  agrees 
with  van  Deen  in  denying  that  the  gray  matter  of  the  cord  can  be 
made,  by  direct  stimulation,  to  originate  either  motor  or  sensory 
impulses.  It  affords  paths,  however,  for  the  transmission  of  both 
these  kinds  of  impulse  when  once  started  by  the  other  nervous  ele- 
ments. Schiff  accordingly  speaks  of  the  posterior  gray  columns, 
and  of  those  parts  of  the  posterior  white  columns  which  are  not 
direct  prolongations  of  the  nerve-roots,  as  "  cesthesodic."  The  corre- 
sponding parts  of  the  anterior  cord  he  calls  "kinesodic."  The  sen- 
sitiveness of  the  posterior  columns  which  others  discover  on  experi- 
ment he  regards  as  only  indirect.  Vulpian,"  on  the  contrary,  agrees 
with  Bell,  Magendie,  Flourens,  and  Longet,  in  holding  that,  while 
the  gray  matter  is  absolutely  inexcitable  and  the  posterior  columns 
very  excitable,  the  anterior  columns  possess  only  a  moderate  degree 
of  excitability. 

'  See,  especially,  articles  in  Pfliiger's  Archiv,  xxviii.,  pp.  537-555,  and  xxix., 
pp.  537-555. 

■-'  Du  Bois-Reymond's  Archiv,  1867,  p.  198 ;  and  Pfliiger's  Archiv,  ii.,  p.  414. 

•'Pfliiger's  Archiv,  xxii.,  pp.  169-176. 

■■  Archiv  f.  Anat.  u.  Physiol.,  1883,  Physiolog.  Abth.,  pp.  283  fE. 

'■  Pfliiger's  Archiv,, xxix. ,  p.  598. 

•^  Legons  sur  la  Physiologie  du  Systeme  nerveux,  p.  362. 


INFLUENCE    OF   THE   BRAIN    OlST   THE   CORD.  143 

By  an  ingenious  arrangement  for  applying  the  mechanical  stimu- 
lus of  pricks  from  an  extremely  fine  needle-point  to  definitely  cir- 
cumscribed spots  in  the  spinal  cord  of  the  frog,  E.  A.  Birge '  seems 
to  have  demonstrated  the  susceptibility  of  the  ganglion-cells  to  di- 
rect stimulus.  Pricking  these  cells  produces  movements  in  defi- 
nitely located  groups  of  muscles  ;  and  the  te  tanusis  invariably 
confined  to  the  muscles  of  the  same  side  as  that  of  the  cells  stimu- 
lated, unless  (as  microscopic  examination  shows)  the  effect  of  the 
needle  has  reached  certain  cells  on  the  other  side.  Birge  also 
found  that  different  regions  of  a  single  cross-section  of  the  cord  are 
excitable  in  different  degrees  ;  the  region  from  the  posterior  fissure 
to  the  median  line  of  the  gray  matter  being  most  inactive,  and  that 
of  the  large  ganglion-cells  in  the  anterior  horn  sinvariably  being 
able  to  produce  tetanus. 

In  view  of  such  conflict  of  testimony  it  can  only  be  said  that 
certain  longitudinal  parts  of  the  spinal  cord  are  plainly  susceptible 
to  direct  stimulation,  but  at  present  it  is  difficult  to  decide  which 
parts,  exclusively,  ai'e  sensitive. 

§  13.  Thus  far  the  spinal  cord  has  been  considered  as  a  series  of 
related  centres,  that  act  automatically  or  reflexly  when  separated 
from  the  brain.  But  in  its  normal  condition  the  cord  always  acts, 
of  course,  under  the  influence  of  the  brain.  The  brain  thus  exer- 
cises a  profound  modifying  influence  over  the  automatic  and  reflex 
activities  of  the  inferior  organ.  The  cord  alone  can  be  dej)ended 
upon,  as  it  were,  to  respond  with  great  regularity,  in  the  form  of 
definite  reflex  movements,  to  a  given  amount  of  stimulus,  when 
applied  at  a  given  locality.  But  the  action  of  the  brain,  when  at- 
tached to  the  cord,  interferes  with  this  regularity,  so  that  the  ex- 
pected muscular  movements  may  not  result  when  the  stimulus  is 
applied.  They  are  then  said  to  be  inhibited  by  the  action  of  the 
brain.  The  phenomena  of  "inhibition,"  when  connected  with  vo- 
lition, are  familiar  enough ;  for  example,  one  may  voluntarily  re- 
strain those  movements  of  one's  legs  which  the  cord,  if  left  to  it- 
self, would  produce  as  the  result  of  tickling  the  soles  of  the  feet. 

But  the  brain  without  conscious  volition  exercises  the  same  in- 
hibitory action  over  the  spinal  cord.  If  a  frog  is  suspended  by  the 
head,  and  its  legs  allowed  to  dip  into  a  vessel  of  dilute  acid,  the  in- 
terval between  the  contact  of  the  acid  and  the  withdrawal  of  the 
legs  is  considerably  lengthened  when  the  spinal  cord  remains  un- 
divided below  the  medulla  oblongata  ;  that  is  to  say,  the  cord  alone 
withdraws  the  legs  quicker  than  the  cord  when  influenced,  or  in- 
hibited, by  the  brain.  The  interval  between  tlje  application  of  the 
'  Arcliiv  f.  Anat.  u.  Physiol  ,  1882,  Physiolog.  Abth.,  pp.  481-489. 


144        THE  BRAIN  AS  A  CENTRAL  ORGAN. 

acid  and  the  contraction  of  the  muscles  can  also  be  prolonged,  when 
the  brain  is  still  connected  with  the  cord,  by  applying  chemical 
irritation  at  the  same  time  to  the  optic  lobes  ;  that  is  to  say,  the 
cord  is  hindered  from  performing  its  reflex-motor  function  by  the 
stimulation,  and  consequent  influence  upon  itself,  of  the  higher 
nervous  centre.  Moreover,  if  at  the  time  that  one  leg  of  a  brain- 
less frog  is  dipped  into  the  acid,  the  sciatic  nerve  of  the  other  is 
strongly  stimulated  with  an  interrupted  current,  the  same  prolon- 
gation of  the  period  of  incubation  will  be  observed  ;  in  some  cases, 
indeed,  the  reflex  act  will  not  take  place  at  all.  In  discussing  the 
reciprocal  relations  of  the  higher  centres  of  the  brain,  we  shall  dis- 
cover many  phenomena  similar  to  the  foregoing.  All  these  centres 
may  exercise  this  so-called  "  inhibitory  "  action  upon  other  centres, 
according  to  their  several  physiological  connections.  The  phenom- 
ena of  inhibition  are  not,  therefore,  confined  to  the  influence  of  the 
brain  on  the  spinal  cord. 

Elaborate  attempts  have  been  made  to  point  out  a  special  mech- 
anism of  inhibition.  Thus  Setschenow '  has  advocated  the  view 
that  localized  inhibitory  centres  exist  in  the  brain,  and  that  the  de- 
pressing effect  travels  by  certain  definite  tracts  in  the  spinal  cord. 
But  on  this  subject  our  doubts  are  entitled  to  go  even  beyond  the 
remark  of  Terrier  :  ^  "  The  nature  of  the  inhibitory  mechanism  is 
exceedingly  obscure."  We  cannot  be  said  to  have  sufficient  grounds 
for  assuming  the  existence  of  any  such  specific  mechanism.  In 
general,  nerve-commotions  modify  each  other  within  the  central 
organs  ;  they  either  facilitate  and  increase,  or  inhibit  and  diminish, 
each  other's  effect,  according  to  the  structure  and  functions  of  the 
organs,  the  amount  and  kind  of  stimulus  thrown  in  upon  them  from 
without,  and  the  exact  condition  in  which  this  stimulus  finds  them. 
The  inhibition  of  the  cord  by  the  brain  is,  then,  only  a  special  case 
under  the  general  molecular  theory  of  the  nervous  mechanism. 
The  factors  entering  into  every  such  case  will  very  likely  always 
prove  too  varied  and  complex  to  be  analyzed  with  complete  success. 

§  14.  On  passing  from  the  spinal  cord  into  thfe  brain,  the  diffi- 
culty of  defining  the  specific  functions — whether  automatic  or  re- 
flex—of the  different  central  organs  becomes  greatly  increased. 
The  phenomena  are  vastly  more  complicated,  and  the  methods  of 
analyzing  them  experimentally  much  less  readily  applied.      The 

'  TJeber  d.  Hemmungsmeohanismen  f.  d.  Reflexthatigkeit  im  Gehirn  d. 
Frosches,  Berlin,  1863  ;  and  other  papers. 

'-functions  of  tlie  Brain,  London,  1876,  p.  18,  where  he  refers  to  the 
elaborate  paper  on  Inhibition  in  the  West  Riding  Reports,  vol.  iv.,  by  Dr.  L 
Brunton. 


THE   METHODS    OF    RESEARCH.  145 

most  complex  portions  of  the  nervous  substance,  in  respect  both 
to  structure  and  to  function,  are  most  completely  withdrawn  from 
the  use  of  strictly  scientific  methods  of  research.  "What  is  known, 
however,  of  the  anatomical  structure  and  connections  of  the  dif- 
ferent organs  of  the  brain,  and  of  the  paths  along  which  the  ner- 
vous impulses  are  propagated  between  them,  prepares  the  way  for 
the  more  specific  physiology  of  eacli  organ.  The  methods  of  such 
physiological  research  are  in  general  these  two  :  Observation  of  the 
results  which  follow  the  application  of  stimulus  to  each  of  the  en- 
ceiDhalic  organs,  or  to  any  definite  locality  in  each  ;  and  observation 
of  the  results  which  follow  the  total  extirpation  or  lesion  of  these 
organs,  or  of  any  portion  of  each.  Of  course,  both  of  these 
methods  are  almost  wholly  applicable  only  to  the  lower  animals. 
In  using  the  method  of  stimulation,  the  stimulus  cannot  be  ap- 
plied to  the  nervous  substance  of  the  brain  without  a  certain 
amount  of  injury  to  that  substance.  To  stimulate  any  of  the  cranial 
organs  with  precision  they  must  be  exposed  ;  those  that  lie  deepest 
cannot  be  exposed  without  injury  to  other  organs  and  the  death  of 
the  animal.  Moreover,  it  is  diflftcult  jjrecisely  to  circumscribe  the 
application  of  the  stimulus.  Just  that  form  of  stimulus  which  is 
most  convenient,  effective,  and  fruitful  in  results — namely,  the 
electrical  current — is  liable  to  diffuse  its  direct  effects  beyond  the 
region  which  it  is  desired  to  circumscribe.  When  no  result  follows 
the  application  of  the  current  to  a  definite  locality  of  the  nervous 
substance,  the  failure  may  be  due  to  the  weakness  of  the  stimulus, 
or  to  the  fact  that  this  particular  centre  is  at  the  moment  inhib- 
ited by  its  condition  or  by  the  activity  of  some  connected  centre. 
When  a  result  does  follow,  it  may  be  that  this  particular  result  is 
due  to  the  direct  or  indirect  stimulation  of  some  other  so-called 
centre,  or  to  the  stimulus  hitting,  by  diffusion  or  otherwise,  some 
of  the  contiguous  sensory  or  motor  nerve-tracts. 

Objection  may  also  be  raised  against  the  nature  of  the  argument 
by  which  an  inference  is  drawn  from  the  facts  gained  by  the  sec- 
ond of  the  above-mentioned  methods.  Such  argument  not  only  as- 
sumes that  the  activities  which  remain,  when  some  of  the  organs 
of  the  brain  are  partially  or  wholly  destroyed,  belong  to  those 
organs  that  remain,  but  also  that  those  activities  whicii  have  dis- 
appeared belong  to  the  organs  that  have  disapj)eared.  Both  of 
these  assumptions  are,  however,  doubtful,  when  we  come  to  apply 
them  to  the  organs  in  their  normal  condition  and  connections 
under  the  action  of  natural  stimuli ;  the  latter  of  the  two  is  partic- 
ularly doubtful.  In  a  word,  the  different  mechanisms  of  the  human 
brain,  in  their  normal  condition  and  relations,  constitute  an  in- 
10 


146  THE    BP.AIlSr    AS    A    CENTEAL    ORGAN". 

ter-clejoendent  and  intimately  related  system  ;  what  each  so-called 
organ  or  centre  does,  or  can  do,  depends  not  only  upon  its  own 
structure  and  condition  at  the  time,  but  also  upon  the  condition 
and  behavior  of  the  other  organs  and  centres  at  the  same  time. 
Such  interde23endence  extends  not  only  to  those  divisions  which 
gross  anatomy  can  mark  off  and.  consider  under  the  name  "the 
organs  of  the  brain,"  nor  simply  to  those  minuter  subdivisions 
which  histology  can  distinguish  by  aid  of  the  microscope  ;  it  doubt- 
less also  extends  to  the  last  details  of  that  molecular  mechanism 
which  the  brain-substance  is.  These  details  are  different  for 
every  individual  animal,  and  for  every  individual  case.  Specific 
differences  belonging  to  the  different  species  of  animal  life,  as  well 
as  those  idiosyncrasies  with  which  pathology  is  familiar,  must  alike 
be  recognized.  It  is  by  no  means  strange,  then,  that  the  physi- 
ology of  the  brain  is  able  only  very  slowly  and  imperfectly  to  win 
from  nature  the  truth,  and  to  remove  the  reproach  of  apparently 
conflicting  facts. 

In  spite  of  the  above-mentioned  difiiculties  certain  results  may 
be  claimed  as  resting  upon  more  or  less  of  clear  evidence  regard- 
ing the  specific  automatic  and  reflex-motor  functions  of  those  inter- 
cranial  organs  that  lie  inferior  to  the  cerebral  hemispheres.  The 
case  of  these  hemispheres  themselves  will  be  subsequently  consid- 
ered in  detail.  For  they  are  those  portions  of  the  nervous  mechan- 
ism about  the  immediate  correlation  of  which  with  the  phenomena 
of  consciousness  there  can  be  no  doubt.  Since  we  are  now  con- 
sidering the  nervous  system  and  its,  central  organs  merely  as  a 
physical  mechanism,  we  definitely  rule  out,  as  far  as  possible,  all 
allusion  to  any  special  relation  between  it  and  the  phenomena  of 
self-conscious  mind. 

§  15.  Besides  the  spinal  cord,  the  Medulla  Oblongata  is  the  cen- 
tral organ  concerning  whose  automatic  and  reflex-raotor  functions 
the  largest  amount  of  precise  information  exists.  The  reflex-motor 
functions  of  this  organ  are  more  intricate  and  of  a  higher  order 
than  those  belonging  jjrimarily  to  the  cord.  They  are  especially 
such  as  stand  related  to  the  vital  functions  of  the  heart  and  blood- 
vessels ;  to  respiration  and  its  allied  movements  of  the  organs  in 
coughing  and  sneezing,  etc. ;  to  the  movements  of  the  muscles  in 
swallowing  and  vomiting  ;  to  the  mimetic  movements  of  laughing, 
weeping,  etc.  Among  the  different  movements  in  the  execution  of 
which  the  medulla  oblongata  is  concerned,  some  are  more  purely 
reflex  and  some  less  so.  Thus  one  cannot  swallow  if  the  sen- 
sory tracts  from  the  throat  to  this  central  organ  are  broken  ;  but 
the  movements  of  the  heart  and  lungs  continue  after  the  reflex- 


THE   MEDULLA   AS   AUTOMATIC.  147 

motor  paths  to  them  are  destroj-ed.  Sensory  stimulations  of  the 
medulla  oblongata,  as  a  rule,  occasion  reflex  movements  by  second- 
ary stimulation  of  a  number  of  motor  tracts.  Swallowing,  sneezing, 
coughing,  shedding  of  tears,  changes  in  respiration  and  in  the 
movements  of  the  heart,  contortions  of  the  countenance,  may  all 
be  occasioned,  through  the  mediation  of  this  organ,  by  one  and  the 
same  sensory  impulse.  There  is  also  a  marked  difference  in  the 
extent  of  the  domain  over  which  the  motor  results  of  stimulating 
the  different  sensory  paths  connected  with  the  medulla  spread 
themselves.  Stimulation  of  the  optic  nerve  occasions  only  very 
limited  reflex  movements,  such  as  the  winking  of  the  eyes,  the  se- 
cretion of  a  few  teai's,  and  a  slight  tendency  to  sneeze.  Stimula- 
tion of  the  nerves  of  taste  extends  over  a  wider  area  of  motor 
tracts  ;  that  of  the  palate  and  lar^^nx  still  wider. 

§  16.  The  most  important  reflex  centres  of  the  medulla  oblon- 
gata are  also  automatic  ;  of  such  centres  he  chief  ai"e  those  con- 
nected with  breathing,  the  movements  of  the  heart,  and  the  inner- 
vation of  the  blood-vessels.  The  excitation  in  these  cases  must  be 
considered  as  a  neural  process  arising  within  the  central  organ 
itself.  The  cause  of  its  origin  is  doubtless  to  be  found  in  the 
changes  that  occur  in  the  supply  and  character  of  the  blood.  Not 
only  all  abnormal  conditions  of  respiration,  like  dyspnoea  and 
apncea,  but  also  the  rhythm  of  normal  respiration,  are  dej)endent 
upon  the  changing  condition  of  the  blood  with  respect  to  its  more 
or  less  perfect  oxidation.  The  stimulus  to  action  of  the  respiratory 
centre  in  the  medulla,  from  the  condition  of  the  blood,  may  be  in 
part  reflexly  applied  through  the  peripheral  ends  of  the  afferent 
nerves  in  various  parts  of  the  body  ;  but  the  main  effect  is  doubt- 
less produced  by  the  direct  action  of  the  blood  on  this  centre.  Its 
rhythmic  nervous  action  may  then  very  well  be  dependent  upon  the 
rhythmic  action  of  the  lungs,  and  upon  the  resulting  periodic  re- 
oxidation  of  the  blood.  For  the  nervous  substance  of  the  medulla 
oblongata  seems  to  be  peculiarly  susceptible  to  the  condition  of 
the  blood. 

§  17.  This  small  central  organ  into  which  the  spinal  cord  ex- 
pands on  entering  the  skull  may  then  be  said  to  be  thickly 
crowded  with  reflex  and  automatic  centres.  To  speak  of  the  more 
important  will  best  serve  to  exhibit  what  is  known  of  its  mech- 
anism. 

The  respiratory  centre  was  first  located  by  Flourens  in  that  part 
of  the  medulla  oblongata  which  serves  as  the  place  of  origin  for 
the  vagus  nerve,  and  then  more  definitely  in  the  V-shaped  apex 
of  the  fourth  ventricle,  or  beak  of  the  calamus  scriptorius.     Since 


148  THE   BRAIlSr   AS   A   CENTRAL   ORGAN. 

extirpation  or  injury  of  this  small  portion  of  the  nervous  sub^ 
stance,  when  all  other  parts  of  the  body  are  left  intact,  causes 
immediate  and  final  cessation  of  respiration,  Flourens  called  it  the 
"  vital  knot  "  (nceud  vital).  Foster  '  locates  this  centre  below  the 
vaso-motor  centre,  and  between  it  and  the  calamus  HcriptorUis. 
Schiff  concludes  that  it  is  double,  and  Hes  on  either  side  in  the 
region  of  the  anterior  part  of  the  ala  cinerea  ;  the  function  of  each 
side,  he  thinks,  is  separate.  In  case  of  need  it  may  be  shifted 
slightly  backward  toward  the  spinal  cord.  The  efforts  of  Gierke '' 
to  fix  it  in  a  definite  gi"oup  of  ganglion-cells  were  not  successful. 
With  this  same  centre  all  the  modifications  of  respiration  in  sigh- 
ing, sobbing,  yawning,  crying,  laughing,  coughing,  sneezing,  and 
hiccoughing  are  connected. 

A  nervous  centre  intimately  connected  with  the  vaso-moto?'  sys- 
tem of  the  different  parts  of  the  body  exists  in  the  middle  part  of 
the  medulla  oblongata.  Since  we  cannot  examine  experimentally 
the  efi'ect  upon  the  action  of  this  centi-e  which  would  be  produced 
by  severing  all  the  afferent  nerves  that  lead  into  it,  we  cannot 
demonstrate  dii'ectly  how  much  of  its  action  is  automatic,  how 
much  reflex.  It  is  probably  both  automatic  and  reflex.  But  the 
removal  of  the  parts  in  frout  of  the  medulla,  inclusive  of  the  cor- 
pora quadrigemina,  exercises  no  perceptible  influence  on  the  blood- 
pressure.  The  principal  vaso-motor  centres  in  the  brain  are  then 
found  in  this  portion  of  the  medulla  oblongata.  Through  it  reflex 
motions  are  called  forth  of  the  most  different  kinds,  and  involving 
muscles  widely  separated  from  each  other  and  from  the  region  of  the 
skin  where  the  stimulus  is  applied.  Witness  the  effect  of  a  draught 
of  air  upon  the  circulation  of  the  blood.  The  arteries  of  a  i-abbit's 
ear  can  be  made  to  contract  by  stimulating  any  one  of  more  than  a 
half-dozen  different  sensory  nerves,  including  the  sciatic  plexus.  In 
this  same  central  organ  must  be  located  the  so-called  cardio-inhib- 
itory  centre.  In  cases  where  the  heart  is  stopped  by  sudden  and 
great  emotion,  or  by  severe  pain,  the  stimulus  probably  reaches  the 
medulla  from  the  hemispheres  of  the  brain. 

The  centre  of  deglutition  lies  in  the  medulla  higher  up  than  that 
of  respiration.  If  this  part  of  the  organ  be  destroyed,  swallowing 
is  impossible.  This  centre  has  been  located  in  the  floor  of  the 
fourth  ventricle.  In  the  floor  of  the  same  ventricle,  and  in  the 
adjoining  region,  are  j^i'obably  located  centi-es  for  different  secre- 
tions— as,  for  example,  of  spittle,  or  sweat,  of  tears,  and  possibly 
of  the  pancreatic  and  other  digestive  juices.     The  connection  of 

'  Text-Book  of  Physiology,  p.  370. 
"  See  Ptliiger's  Arcliiv,  vii. ,  pp.  583  ff. 


INFLUENCE    OF   MEDULLA    ON   THE    LIMBS.  149 

various  sensations  and  emotions  with  these  secretions  is  too  famil- 
iar to  need  description.  A  central  mechanism  for  winking  the 
eyes  Esner  would  place  near  the  beak  of  the  calamus  scriptoriun. 
The  centi-al  mechanism  for  the  reflex  movement  of  the  muscles  of 
the  oesophagus  and  stomach  also  lies  in  the  medulla  oblongata.  Of 
the  centre  for  the  production  of  artificial  diabetes,  and  of  other 
more  conjectural  centres  which  are  packed  within  this  small  bit 
of  nervous  matter,  scarcely  more  than  an  inch  in  length,  we  do  not 
need  to  speak. 

§  18.  The  alleged  functions  of  the  medulla  oblongata  in  the  co- 
ordination of  the  movements  of  the  skeletal  muscles  ally  this  organ 
more  closely  with  certain  other  inferior  parts  of  the  brain.  The 
prepai\ation  of  a  frog  which  has  retained  this  organ,  in  addition  to 
the  spinal  cord,  although  without  any  of  the  rest  of  the  brain,  will 
execute  movements  of  the  muscles  that  are  not  possible  for  the  cord 
alone.  It  will  not,  indeed,  move  spontaneously  ;  it  still  requires 
external  stimulation  to  start  the  mechanism  of  such  a  preparation. 
Under  such  stimulation,  however,  it  will  assume  a  j)ositiou  natural 
to  it  in  an  uninjured  state.  When  laid  on  its  back  it  will  make 
efforts— generally  unsuccessful — to  turn  over.  The  movements  of 
the  limbs  with  which  it  responds  to  various  sensory  impulses  are 
more  complicated  than  those  executed  by  the  spinal  cord  alone  ; 
they  even  resemble  crawling  motions  or  short  leaps.  Placed  in  the 
water,  what  is  left  of  the  animal  will  swim  ;  and  if  its  motions  are 
less  perfect  than  those  of  the  perfect  frog,  they  are  much  more  so 
than  those  of  the  cord  alone.  It  is  doubtful  whether,  when  placed 
beneath  the  water,  it  will  ascend  to  the  surface  to  breathe,  or 
make  efforts  to  escape  from  water  gradually  heated  to  about  104° 
Fahr., — as  will  the  animal  that  retains  its  cerebellum  and  optic 
lobes. 

Reflex  movements  of  considerable  complexity  can  also  be  exe- 
cuted by  mammals  that  have  been  deprived  of  all  the  enceiDhalic 
centres  above  the  medulla.  Vulpian  claims  that  a  yoang  rat  in 
this  condition  will  emit  a  cry,  as  of  pain,  when  its  toes  are  pinched. 
Such  a  mechanism  will  swallow  and  execute  cei-taiu  co-ordinated 
movements  of  the  limbs.  Infants  whose  nervous  centres  above  the 
medulla  are  undeveloped  will  perform  the  associated  movements 
of  sucking  when  put  to  the  breast.  Moreover,  the  effects  of  le- 
sion of  the  centres  of  the  medulla  are  very  marked  in  respect  to  the 
co-ordination  of  motion.  Eolando  observed  that  convulsive  move- 
ments followed  extensive  injury  of  this  central  organ.  More  recent 
researches  seem  to  show  that  the  seat  of  these  epileptiform  move- 
ments is  at  the  place  of  union  between  the  medulla  and  the  pons  ; 


150        THE  BRAIN  AS  A  CENTRAL  ORGAN. 

it  can,  therefore,  scarcely  be  located  in  either  alone.'  One-sided 
lesions  are  followed  by  certain  so-called  "  forced  "  and  rotai-y  move- 
ments of  the  head,  and  eyes,  and  trunk.  Such  effects  are  most 
likel}'  to  be  produced  when  the  injury  affects  the  region  of  the 
taherculum  acusticum.  In  the  opinion  of  Bechterew  "  the  olivary 
bodies  are  in  relation  with  the  gray  matter  of  the  third  ventricle, 
and  with  the  semicircular  canals,  as  central  organs  for  the  co-or- 
dination of  the  muscles  used  in  balancing  according  to  impressions 
of  touch.  It  would  then  be  one  chief  function  of  the  medulla  to 
secui'e  equipoise  through  these  sensory  impressions.  On  the 
whole,  it  appears  certain  that  considerable  work  in  co-ordinating 
the  muscular  movements  falls  upon  its  mechanisms.  Of  such  work 
it  is  probable  that  the  movements  concerned  in  articulate  speech 
are  a  part.  Any  indirect  relation  which  it  may  have  to  the  produc- 
tion of  those  sensations  and  images  which  are  woven  into  our 
dreams  does  not  belong  in  this  connection. 

§  19.  The  associations  among  the  different  centres  of  the  me- 
dulla oblongata  are  curious  enough ;  they  involve  an  extremely 
intricate  physiological  apparatus.  Some  of  these  centres  are  in- 
directly connected  with  psychical  activities.  They  are  not  all  alike 
excitable  ;  they  are  not  all  voluntarily  so.  Thus  we  can  volun- 
tarily control,  within  certain  limits,  the  movements  of  the  lungs, 
but  not  those  of  the  heart  and  blood-vessels  ;  we  can  cough,  but 
cannot  sneeze,  at  wiU.  Some  of  their  functions  are  associated 
together  regularly  ;  some  of  them  seldom  ;  some  never.  Swallow- 
ing is  not  necessarih'  connected  with  the  activity  of  the  other  cen- 
tres, unless  it  be  with  that  for  the  secretion  of  saliva  ;  it  takes 
place,  however,  during  arrest  of  respiration.  The  excitation  of  no 
other  centre  necessarily  affects  this  centre.  The  secretion  of  saliva 
is  constantly  connected  with  a  change  in  the  circulation  through 
the  submaxillary  glands. 

§  20.  An  animal  which  possesses  all,  or  a  considerable  part  of 
the  other  nervous  mechanisms  of  the  brain  that  lie  below  the  cere- 
bral hemispheres  is  capable  of  executing  movements  which  differ 
greatly  from  those  already  described  as  belonging  to  the  spinal 
cord  and  medulla  oblongata.  Very  few  of  the  movements  of  such 
a  preparation  are,  indeed,  even  apparently  spontaneous ;  for  al- 
most all  of  them  a  definite  form  and  degree  of  stimulus  acting  on 
the  sensory  surfaces  can  be  assigned.  We  are  inclined,  then,  to  sus- 
pect that  those  movements  which  are  apparently  spontaneous  are 
really  due  to  some  stimulation  from  wdthout  the  central  organs 

'See  Eckliard,  in  Hermann,  Handb.  d.  Physiol.,  II.,  ii.,  p.  98. 
'Pfluger's  Archiv,  xxxi.,  pp.  479  If.,  aud  xxix.,  p.  258 f. 


IlSTFLUEISrCE    OF   THE    CEREBEAL   LOBES.  151 

which  has  escaped  our  observation.  But  the  range  of  reflex-motor 
activities  vrhich  an  animal  deprived  simply  of  its  cerebral  hemi- 
spheres will  execute,  in  i-esponse  to  appropriate  stimuli,  is  very 
great ;  it  may  be  said  to  include  every  form  of  movement  possible 
for  the  uninjured  animal.  The  statement  is,  therefore,  wan-anted 
by  all  our  knowledge  of  the  facts,  that  the  medulla,  pons,  crura 
cerebri,  cerebellum,  corpora  quadrigemina  (or  optic  lobes),  and 
basal  ganglia  generally  are  the  special  mechanism  for  co-ordi- 
nating the  movements  of  the  muscles  with  the  various  impulses  of 
sense. 

A  frog  from  which  the  cerebral  lobes  have  been  removed  will 
respond  to  appropriate  stimuli  with  all  the  movements  of  which  a 
perfect  frog  is  capable.  It  will  swim,  leap,  and  crawl.  When 
placed  on  its  back,  it  will  easily  and  at  once  regain  its  natural  posi- 
tion. When  placed  on  a  tilting  board,  it  will  constantly  adjust 
the  position  of  its  body  so  as  to  maintain  an  equilibrium.  It  will 
croak  with  the  regularity  of  a  music-bos  when  its  flanks  are  gently 
stroked.  Thrown  into  the  water  it  will  swim  with  great  regularity 
of  motion  until  it  is  exhausted  or  finds  something — as  a  small  piece 
of  wood  placed  in  contact  with  it — upon  which  it  can  crawl.  When 
submerged  in  the  water,  it  will  rise  to  the  surface  for  air ;  it  wall 
not,  like  a  mere  spinal  cord,  remain  quietly  in  water  the  temper- 
ature of  which  is  gradually  raised,  but  will  make  violent  efibrts  to 
escape.  It  is  guided  by  the  light,  for  it  avoids  objects  that  cast  a 
strong  shadow.  On  the  other  hand,  it  appears  stupid  ;  it  jDays  no 
attention  to  the  flies  that  are  placed  near  it ;  by  careful  exclusion 
of  all  stimuli  it  may  be  kept  motionless  for  hours.  We  cannot 
argue  from  this,  however,  that  it  is  without  sensations,  for  it  may 
not  be  hungry  ;  and  Heubel '  asserts  that  a  sound  frog  may,  with 
careful  manipulation,  be  made  to  lie  still  upon  its  back  for  a  long 
time. 

Similar  phenomena  occur  in  the  case  of  the  mammal  whose  cere- 
bral hemispheres  have  been  removed.  The  rabbit  or  rat  thus 
operated  upon  will  stand  and  run  and  leap.  Placed  on  its  back, 
it  will  regain  its  feet.  It  will  follow  with  its  head  a  bright  light 
held  in  front  of  it ;  it  will  start  and  tremble,  or  run,  at  a  shrill  or 
loud  noise.  It  will  utter  a  prolonged  cry  when  pinched.  Its  mus- 
cular motions  are  obviously  co-ordinated  in  response  to  sensory 
impulses  from  the  organs  of  touch,  hearing,  and  sight.  The  bird 
thus  operated  upon  will  easily  regain  its  feet  when  laid  upon  its 
side  or  back,  and  will  stand  in  a  natural  and  easy  posture.  It  will 
tuck  its  head  under  its  wings,  clean  its  feathers,  and  pick  up  corn 
'  Pfluger's  Archiv,  xiv. ,  pp.  163  ff. 


152        THE  BRAIN  AS  A  CENTEAL  ORGAN. 

or  drink  water  presented  to  its  beak.  Thrown  into  the  air,  it  will 
fly  with  considerable  precision  for  some  distance,  and  in  its  flight 
will  guide  itself,  though  imperfectly,  so  as  to  avoid  obstacles  in  its 
way.  It  will  start  at  sharp  sounds  or  flashes  of  light.  Such  ani- 
mals have  on  the  whole  the  appearance  of  being  sleepy  and  stupid 
rather  than  of  being  deprived  of  any  of  their  powers  for  co-ordi- 
nating sensation  and  motion.  We  conclude,  then,  that  the  organs 
which  such  animals  possess  are  functionally  capable  of  exex'cising 
all  these  powers  of  co-ordination  ;  we  do  not  at  present  raise  the 
question  whether  this  implies  the  existence  of  psychical  j)henomena 
or  not.  The  phenomena  which  follow  the  partial  loss  of  the  cere- 
bral hemispheres  in  the  higher  mammals  confirm  the  same  conclu- 
sion. 

It  is  much  more  difficult,  however,  to  assign  the  special  place 
which  belongs  to  each  of  the  organs  that  lie  between  the  medulla 
oblongata  and  the  cerebral  hemispheres,  under  their  general  func- 
tion as  already  stated.  They  are  all  very  intimately  related  ;  act 
to  a  large  extent  dependently  ;  can,  within  certain  limits,  assume 
each  other's  functions  ;  and  have  largely  the  same  connections  with 
the  peripheral  organs  of  sense  and  of  motion,  and  the  same  Avork 
to  do  as  mediating  between  the  two. 

§  21.  It  is  impossible  to  determine  the  special  functions  of  the 
Cerebellum,  so  conflicting  is  the  testimony  of  different  experiment- 
ers. A  high  degree  of  probability,  however,  attaches  itself  to  the 
statement  that  this  organ  is  largely  concerned  in  the  co-ordination 
of  motion  ;  although  such  statement  cannot  be  held  to  exhaust  its 
functions.  The  more  specific  theory  of  Wundt ' — "It  is  the  central 
organ  that  brings  such  movements  of  the  animal's  body  as  are  ex- 
cited by  impulses  from  the  cerebrum,  into  accord  with  its  situation 
as  a  whole  in  space" — is  more  doubtful,  precisely  because  it  is 
more  specific.  Comparative  anatomy  seems  to  show  that  the  office 
of  the  cerebellum  in  some  animals  differs  from  its  office  in  man  ; 
reasoning  from  the  former  to  the  latter  is,  therefore,  especially  pre- 
carious. Moreover,  its  functions  are  so  closely  connected  anatom- 
ically with  those  of  the  pons,  the  crura  cerebri,  and  the  medulla, 
that  it  is  difficult  precisely  to  separate  its  work  from  that  done  by 
these  organs. 

Testimony  as  to  the  result  of  the  extirpation  or  lesion  of  the  cere- 
bellum is  vei-y  conflicting.  Apparently  almost  the  entire  length 
and  breadth  of  its  surface  (in  the  direction  of  the  posterior  bones 
of  the  skull),  and  not  only  the  gray  matter,  but  also  the  white,  as 
far  as  near  the  bifurcation  of  its  strands,  may  be  removed  without 
'Grundzuge  d.  physiologische  Psychologie,  i.,  p.  301. 


LESIONS   OF   THE   CEEEBELLUM.  153 

any  observable  result.'  On  approacbing  the  middle  of  its  thick- 
ness and  removing  the  strands  connected  with  the  middle  peduncles, 
disturbances  of  motion  begin  and  increase  rapidly  in  proportion  to 
the  amount  of  substance  removed.  Most  of  these  disturbances,  if 
the  animal  recovers  w^ell,  prove  to  be  only  temporary ;  they  are, 
therefore,  probably  due  largely  to  traumatic  excitation.  Permanent 
disturbances,  however,  occur  when  the  injuries  reach  the  lower 
third  of  the  organ,  or  when  they  are  confined  to  this  third.  Vulpian 
accordingly  concludes  that  the  disturbance  of  gait  which  results 
from  injury  of  the  cerebellum,  is  due  to  the  irritation  of  its  more 
profound  white  parts  or  of  the  adjoining  cerebral  isthmus.  But 
Sehiff  believes  that  the  mass  of  the  organ,  apart  from  locality,  has 
a  definite  influence  upon  the  co-ordination  of  the  bodily  movements  ; 
though  what  that  influence  is  cannot  yet  be  clearly  defined.  The 
influence  of  locality  seems  to  be  considerable  upon  the  effect  which 
results  from  lesions  in  a  given  amount  of  the  cerebellar  substance  ; 
but  since  this  influence  is  much  more  marked  near  the  connections 
of  the  cerebellum  with  other  contiguous  organs,  some  observers 
attribute  it  largel}-  or  wholly  to  the  injury — by  extension  of  the 
lesion,  by  pressure,  or  by  inflammation — of  these  organs.  Thus 
the  place  of  its  union  with  the  medulla  oblongata  and  the  regions 
near  the  crura  cerebri  are  especially  important.  But  Schifi"  found, 
in  experimenting  upon  mammals,  that  complete  vertical  section  of 
the  cerebellum,  in  the  exact  median  line  of  the  vermiform  process, 
and  removal  with  the  knife  or  pincers  of  the  entire  substance,  with 
the  exception  of  the  flocculi  and  the  parts  external  to  the  peduncles, 
produced  no  appreciable  loss  of  the  power  of  co-ordination. 

The  efi'ect  of  one-sided  lesions  of  the  cerebellum  in  the  disturb- 
ance of  motion  seems  to  be,  as  a  rule,  much  more  certain  and 
marked  than  that  of  symmetrical  lesions  of  both  sides.  Sehiff,  in- 
deed, asserts  that  when  a  bilateral  lesion  is  perfectly  symmetrical 
it  pi'oduces  no  impairment  whatever  of  the  functions  of  motion. 
But  the  entire  evidence  from  experiment  shows  that  sudden  lesion 
of  one  hemisphere  of  this  organ  is  almost  uniformly  followed  by 
at  least  temporary  impairment  of  the  motor  functions.  Section  of 
the  middle  peduncle  of  the  cerebellum  of  a  bird  or  mammal  almost 
always  occasions  so-called  "  forced  "  movements  ;  the  animal  rolls 
around  its  own  longitudinal  axis,  generally,  though  not  invariably, 
toward  the  injured  side.  Nystagmus,  or  the  peculiar  rolling  move- 
ment of  the  eyes  suggestive  of  vertigo,  and  strabisrnus,  take  place 

'  Compare  Vulpian,  Lemons  sur  la  Physiologic,  etc.,  pp.  603  ff.;  Eckhard,  in 
Hermann,  Handb.  d.  Physiol.  II.,  ii.,  pp.  102  ff.;  Sehiff,  m  Pfluger's  Archiv., 
xxxii.,  pp.  427  ff. ;  and  Ferrier,  Functions  of  the  Brain,  pp.  85-123. 


154  THE   BRAIjST   as   A   CENTRAL   ORGAK. 

in  such  cases.  One  eye  may  be  moved  inward  and  downward,  the 
other  outwai-d  and  upward.  Hitzig  '  and  Ferrier  °  found  the  same 
results  to  follow  injm-y  of  the  lateral  lobe.  The  latter  observed  that 
strong  stimulation  of  the  cerebellar  surface  with  the  interrupted 
current  causes  associated  movements  of  the  eyes  and  head  and 
hmbs,  in  cats  and  dogs  and  monkeys.  But  these  effects  may 
be  largely  due  to  the  connection  of  the  cerebellum  with  the  me- 
dulla oblongata. 

The  evidence  from  pathological  cases  in  man  conflicts,  to  a  con- 
siderable extent,  with  the  conclusions  which  we  might  hasten  to 
derive  from  experiment  upon  the  animals.  According  to  Vulpian  ' 
it  is  by  no  means  rare  to  have  unilateral  lesions  of  the  cerebellum 
followed  by  no  paralysis  of  either  side.  In  a  gTcat  number  of  such 
cases  no  genuine  hemijDlegia  results ;  the  resulting  enfeeblement  of 
motion,  moreover,  is  as  often  on  the  same  as  on  the  opposite  side. 
M.  Andral  is  said  to  have  made  a  collection  of  ninety-three  cases 
of  diseases  of  the  cerebellum,  in  only  one  of  which  ataxy  was  ob- 
served in  any  marked  way.  In  most  cases  where  crossed  hemi- 
plegia does  result,  Vulpian  thinks  it  due  to  the  destruction  or 
compression  of  the  adjacent  parts,  especially  the  roots  of  the  cere- 
bellar peduncles.  The  same  authority  denies  that  the  superficial 
parts  of  this  organ  are  excitable,  or  that  lesion  of  them  is  followed 
by  pain  or  by  convulsions  of  the  body,  face,  or  eyes.  Such  results 
do,  however,  follow  excitation  and  lesion  of  its  deeper  parts,  in 
proportion  to  the  degree  of  approach  to  the  peduncles.  The  dis- 
crepancy between  experiment  and  pathology  may  perhaps  be  re- 
moved, at  least  in  part,  by  remembering  that  the  injury  is  sudden 
in  the  one  case  and  not  in  the  other.  Moreover,  few  of  the  patho- 
logical cases  are  clearly  enough  defined  to  serve  as  a  sure  basis  for 
conclusions.  Some  of  them,  however,  would  seem  to  warrant  cer- 
tain inferences.  More  than  fifty  years  since,  the  well-known  case  of 
the  girl  Alexandrine  Labrosse  was  reported  by  Combette,''  and  after- 
ward made  known  to  students  of  physiology  generally  by  Longet.^ 
This  girl  was  found,  on  post  mortem,  to  have  no  cerebellum ;  in  its 
stead  was  a  gelatinous  membrane  attached  to  the  medulla  by  two 
peduncles  of  like  construction.  A  true  pons  was  also  wanting,  but 
no  loss  of  substance  seemed  to  have  taken  place  here.  Yet  she 
could  co-ordinate  all  the  limbs  voluntarily,  and  had  the  f\ill  use  of 

'  Untersuchungen  iiber  d.  Gehirn,  pp.  198  ff. 

^Functions  of  the  Brain,  p.  106  f. 

^  Lef;oiis  sur  la  Physiologie,  etc. ,  p.  607  f. 

*  Revue  madicale,  II.,  p.  57  (1831). 

^  Anatomie  et  Physiologie  du  Systeme  nerveux,  I.,  p.  764  (1842). 


LESIONS   OF   THE   CEREBELLUM.  155 

all  the  senses.  She  was,  however,  subject  to  falling  (se  laissait 
tomber  souvent)  and  spoke  imperfectly.  Bouillaucl  has  reported 
another  case  of  an  adult  whose  entire  cerebellum  was  changed  into 
a  brown  purulent  mass  ;  this  patient  could  walk,  tliough  in  a  tot- 
tering and  insecure  way.  Vulpian  '  also  describes  a  case  which 
came  under  his  own  observation.  A  woman,  dying  at  the  age  of 
sixty-nine,  after  twenty  years  in  the  hospital  of  La  Salpetriere,  was 
found  to  have  suffered  an  entire  atrophy  of  all  the  cortical  gray 
substance  of  the  cerebellum.  This  patient  preserved  great  muscu- 
lar vigor,  and  could  co-ordinate  all  the  muscles  ;  but  her  "locomo- 
tion "  wag  disordered  and  difficult. 

On  the  whole,  then,  it  must  be  admitted  that  the  evidence  con- 
cerning the  sj)ecific  functions  of  the  cerebellum  of  mammals,  and 
especially  of  man,  is  not  such  as  to  warrant  us  in  making  definite 
affirmations.  Scarcely  a  single  case  can  be  adduced  in  which  it 
is  not  j)0ssible  to  maintain  that  the  motor  disturbances  which  fol- 
lowed lesion  or  excitation  of  this  organ  should  be  ascribed  to  an 
indirect  effect  upon  contiguous  organs.  Yet  the  coincidence  of 
evidence  from  several  different  lines  gives  sufficient  support  to  the 
view  that  the  functions  of  the  cerebellum  are  in  some  way  con- 
nected with  the  balancing,  and  therefore  with  the  precise  and  se- 
cure locomotion  of  the  body  in  space.  More  definitely,  with  refer- 
ence to  the  nature  of  this  connection,  it  is  not  possible  to  speak 
confidentl}'.  No  disturbance  of  the  senses  of  hearing,  of  sight,  or 
of  muscular  feeling,  can  be  shown  to  follow  injuries  of  this  organ 
where  other  parts  of  the  brain  are  not  involved ;  on  the  contrary', 
all  these  senses  appear  to  have  been  perfect  in  certain  cases  of  the 
complete  absence  of  this  organ.  The  only  disturbance  of  sensi- 
bility which  frequently  follows  affections  of  the  cerebellum  is  ver- 
tigo ;  the  same  symptom  can  be  produced  by  passing  a  current  of 
electricity  through  the  back  part  of  the  head,  or  by  the  effusions 
of  blood  in  this  region  which  are  sometimes  occasioned  by  alcohol. 
Vulpian  and  others  are,  however,  probably  right  in  holding  that 
the  result  is  only  indirectly  to  be  ascribed  to  this  organ.  Indeed 
the  view  of  Schiff  has  much  in  its  favor  :  this  view  maintains  that 
the  aberration  of  motion  due  to  lesion  of  the  cerebellum  should 
not  be  called  a  loss  of  co-ordination  at  all,  since  all  the  limbs  may 
be  moved  in  exactly  the  right  relations  necessary  to  carry  the  body 
forward  or  to  maintain  its  equipoise  ;  bi,it  the  precision  of  the  mo- 
tion is  impaired,  because  the  nervous  impulses  from  this  organ 
that  innervate  the  neighboring  groups  of  muscles  are  not  rightly 
adjusted  to  each  other  in  amount  along  the  difiereut  tracts.  The 
'  Lemons  sur  la  Physiologic,  etc.,  p.  629. 


156  THE   BRAIN   AS   A    CENTIIAL   OKGAlSr. 

balance  of  the  innervating  cells  is  destroyed  ;  and  the  result  is  a 
loss  of  nice  adjustmeut  of  the  amount  of  innervation  sent  to  the 
particular  muscles  employed  in  equipoise  and  locomotion. 

It  scarcely  need  be  added  that  modern  physiology  distinctly  dis- 
proves the  hypothesis  of  Gall,  who  connected  the  sexual  instinct 
Avith  the  cerebellum.  There  is  no  good  evidence  that  the  hinder 
brain  directly  participates  in  any  way  in  those  activities  of  the 
nervous  system  which  are  immediately  correlated  with  psychical 
phenomena,  whether  of  emotion,  instinct,  or  intelligence. 

§  22.  The  functions  of  only  three  other  parts  of  the  encephalon 
require  consideration  in  this  connection  ;  these  are  the  corpora 
quadrigemina,  the  optic  thalami,  and  the  corpora  striata.  The 
crura  cerebri  and  the  pons  Varolii  are,  as  we  have  already  seen, 
significant  chiefly  as  organs  of  conduction.  So  far  as  they  have 
also  the  intermediating  functions  of  central  organs,  it  is  not  possi- 
ble to  treat  of  them  otherwise  than  as  concerned  in  that  general 
reflex-motor  mechanism  which  occupies  all  this  region  of  the  brain. 

§  23.  Experiments  upon  the  Corpora  Quadrigemina  are  rendered 
especially  difficult  by  the  small  size  and  deep  situation  of  these 
organs ;  they  cannot  easily  be  exposed  for  stimulation  without 
great  effusion  of  blood,  or  subjected  to  lesion  without  extending  the 
injury  to  contiguous  parts.  These  difficulties  render  conclusions 
from  the  effect  of  stimulating  or  extirpating  the  corresponding 
organs  (optic  lobes)  of  the  frog  more  than  usually  precarious. 
There  is  no  doubt,  however,  as  to  some  sj)ecial  connection  between 
the  corpora  quadrigemina  and  sensory  impulses  of  sight ;  such  con- 
nection is,  then,  of  course,  to  be  extended  to  those  motor  activities 
that  are  dependent  upon  the  sensory  impulses  of  sight.  Flourens 
and  many  subsequent  observers  have  found  that  one-sided  extirpa- 
tion of  the  optic  lobes  of  birds,  or  of  the  corpora  quadrigemina  of 
mammals,  with  the  cerebral  hemispheres  intact,  produces  blindness 
in  the  ojDj^osite  eye.  The  amount  of  this  blindness  is  different  in 
different  animals,  as  the  decussation  of  the  fibres  in  the  optic  chi- 
asm is  more  or  less  complete  in  different  animals.  In  the  rabbit 
such  decussation  appears  to  be  complete  ;  in  the  cat  and  dog  in- 
complete. The  fact  that  hemianopsia  in  both  eyes  is  connected 
with  disease  of  one  side  of  the  brain  is  an  evidence  that  it  is  incom- 
plete in  man  also.  Moreover,  when  the  brain  is  removed  in  front 
of  the  corpora  quadrigemina,  and  these  organs  left  intact,  the  ani- 
mal can  still  guide  and  co-ordinate  its  motions  in  response  to  visual 
impulses.  (We  do  not  in  this  place  consider  whether  we  are  war- 
ranted in  calling  these  impulses  "  sensations  " — not  to  say  "percep- 
tions"— of  sight.)     These  organs  are,  then,  in  some  sort,  central 


LESIONS    OF   THE   CORPORA   QUADRIGEMINA.  157 

organs  of  sight.  Since  they  are  connected  by  nerve-tracts  -with  the 
cortex  of  the  cerebrum,  motor  innervation  in  response  to  stimulus 
from  the  optic  nerve  may  arise  either  immediately  in  the  corpora 
quadrigemina  themselves  or  in  the  gray  matter  of  the  cortex.  We 
may  therefore  suppose,  with  Wundt,'  that  destruction  of  the  cere- 
bral substance  abolishes  only  those  movements  of  the  muscles,  in 
response  to  the  stimulus  of  light,  which  involve  complicated  co-or- 
dinations with  other  excitations  of  sense,  or  with  earlier  established 
experience.  It  is  scarcely  allowable,  however,  to  locate  this  special 
relation  to  visual  imjDulses  definitely  in  the  substance  of  the  corpora 
C[uadrigemiua  considered  as  isolated  from  the  optic  thalami,  the 
optic  tracts,  and  the  gray  matter  at  the  floor  of  the  third  ventricle. 
There  is  sound  sense  in  Eckhard's  ^  remark  that  the  functions 
commonly  attributed  to  these  bodies  should  rather  be  ascribed  to 
the  region  in  which  they  lie.  The  nates  (or  anterior  pair)  seem  to 
be  more  especially  connected  with  the  sensory,  and  the  testes  (or 
posterior  pairj  with  the  motor  activities  of  sight. 

Abnormal  movements  of  a  "  forced  "  nature,  and  impairment  of 
the  power  of  co-ordination,  follow  the  injury  or  extii-pation  of  the 
corjDora  quadrigemina.  These  phenomena  may  be  due  in  part  to 
the  loss  of  guidance  by  visual  impressions  ;  but  they  are  probably 
due  chiefly  to  the  extension  of  the  efiiects  of  the  injury  to  the  crui-a 
cerebri  and  other  surrounding  parts.  The  o'^iia  lobes,  according 
to  Groltz,  are  the  principal  central  mechanism  for  the  croaking  of 
the  frog  deprived  of  its  hemispheres.  Vulpian  ^  makes  a  distinction 
between  a  mei^ely  reflex-motor  cry  and  the  plaintive  utterance  of 
an  animal  {e.g.,  the  rabbit)  which  retains  these  organs  and  the  pons 
Varolii.  Ferrier,^  however,  was  unable  to  make  the  distinction  so 
clearly.  The  latter  observer  found  that  very  marked  phenomena — 
such  as  dilating  the  pupils,  clenching  the  jaws,  retraction  of  the 
ears  and  angles  of  the  mouth,  extending  the  legs,  etc. — followed 
the  stimulation  of  these  organs  with  an  electrical  current,  in  the 
case  of  cats  and  dogs.  But  his  experiments  do  not  enable  us  to 
say  how  much  of  all  this  belongs  to  the  specific  function  of  the 
corpora  quadrigemina  as  central  organs,  and  how  much  to  the  irri- 
tation of  the  nerve-tracts  in  all  the  surrounding  region.  "While  we 
seem  warranted  in  connecting  these  organs  with  the  cerebellum, 
medulla,  and  pons,  as  concerned  in  the  co-ordination  of  motions 
necessary  for  equipoise  and  locomotion,  it  is  not  safe  at  present  to 
attempt  a  more  precise  localization  of  function. 

1  Physiologische  Psychologie,  i  ,  p.  184. 

'^  In  Hermauu's  Handb    d.  Physiol.,  II.,  ii. ,  p.  131. 

^  Lecous  sur  la  Physiologie,  etc.,  p.  541  f. 

*  Functions  of  the  Brain,  p.  76. 


158        THE  BEAIN  AS  A  CENTEAL  OEGAN. 

§  24.  The  office  of  the  so-called  basal  ganglia— Optic  Thalami 
and  Corpora  Striata — in  that  "projection-sj^stem"  which  connects 
the  cerebral  hemispheres  with  the  periphery  of  the  body,  has 
already  been  spoken  of;  one  chief  function  of  these  ganglia  has 
usually  been  held  to  be  that  of  acting  the  part  "  of  middleraen  be- 
tween the  cerebral  convolutions  and  the  rest  of  the  brain."  '  But 
they  both  have  further  functions  as  specifically  central  organs  in  co- 
ordinating the  movements. of  the  body  according  to  impressions  of 
sense.  It  is  difficult,  if  not  impossible,  however,  to  define  precisely 
what  these  functions  are.  Some  special  relation  of  the  optic 
thalami  to  impressions  of  sight  must  be  admitted.  The  fact  that 
animals  deprived  of  the  cerebral  hemispheres  are  capable  of  com- 
plex co-ordination  of  their  muscles  as  reflex  effects  of  visual  im- 
pressions, seems  to  indicate  that  the  mechanism  of  the  optic 
thalami  is  associated  with  that  of  the  corpora  quadrigemina  in 
performing  this  function.  In  mammals  complete  extirpation  of 
the  posterior  portion  of  one  thalamus  results  in  permanent  ex- 
pansion of  the  pupil  of  the  opposite  eye  ;  and  Renzi  was  confident 
that  injury  of  the  upper  surface  of  the  anterior  portion  occasioned 
bhndness.  Lussana  and  Lemoigne  found  blindness  in  the  opposite 
eye  to  be  the  invariable  result  of  lesion  of  one  thalamus.  Cases  of 
the  disturbance  of  vision,  or  even  of  complete  blindness,  have  been 
observed  in  human  patients  as  the  apparent  result  of  disorgani- 
zation of  this  organ.  It  must  be  admitted,  however,  that  the  sig- 
nificance of  the  optic  thalami  for  vision  may  be  due  simply  to  the 
fact  that  certain  fibres  of  the  optic  nerve  have  their  origin  in  it, 
and  are  rendered  inoperative  by  injuring  it.  Experiments  and 
jjathological  cases  connecting  the  optic  thalami  with  the  sensations 
of  smell  and  taste  are  more  doubtful  and  conflicting,  Ferrier  ^  con- 
cludes that  lesions  in  and  around  this  organ  destroy  the  cutaneous 
sensation  of  the  opposite  side  of  the  body  in  the  monkey  ;  Veyssiere 
found  the  same  thing  true  in  dogs.  But  Nothnagel  found  that  no 
effect  upon  sensation  followed  the  destruction  of  these  organs  in 
the  rabbit.  Not  a  few  cases  of  disease  of  the  oj^tic  thalami  in  man 
seem  to  point  to  some  connection  with  tactile  imjDressions  ;  other 
cases,  however,  are  decidedly  unfavorable  to  this  view.  On  the 
basis  of  this  rather  meagre  evidence  "Wundt  ^  is  willing  to  rest  the 
theory  that  the  optic  thalami  are  special  centres  for  the  reflex- 
motions  of  touch  ;  by  the  same  theory  he  also  accounts  for  the  dis- 
turbances of   motion  which  follow  injury  to  these   organs.     He 

'  See  Foster,  Text-Book  of  Physiology,  p.  653. 
''■  Functions  of  the  Brain,  pp.  288  ff. 
*  Physiologische  Psychologic,  i. ,  p.  188. 


LESIONS   OF  THE   STRIATE   BODIES.  159 

thinks  it  probable,  nevertheless,  that  their  function  is  not  exhausted 
by  this  description.  "Forced  "  positions  and  movements,  and  various 
other  marks  of  impaired  motor  activities,  follow  the  experimental 
lesion  of  these  organs.  But  such  disturbances  largely  or  wholly 
vanish  after  a  brief  time,  although  they  can  be  again  called  out  by 
stimulation.  They  occur,  as  a  rule,  only  when  the  lesion  affects 
the  posterior  part  of  the  thalamus,  or  the  edges  of  the  opening 
leading  from  above  into  the  third  ventricle.  Most  of  the  phenom- 
ena may  be  explained  as  due  to  the  working  of  a  mechanism  that 
has  been  stimulated  to  abnormal  activity  by  the  mechanical  irrita- 
tion due  to  the  extirpation.'  We  can  scarcely,  then,  be  anymore  ex- 
plicit than  to  quote  the  remark  of  Vulpian,  made  some  years  since  : " 
"We  know  nothing  of  the  special  functions  of  the  optic  thalami." 

§  25.  The  special  motor  significance  of  the  Corjjora  Striata  is 
undoubted  ;  although  we  cannot  go  to  the  length  of  holding  that 
these  bodies  are  concerned  only  in  the  elaboration  and  downward 
transmission  of  efferent  impulses.  Ferrier  ^  and  others  have  ob- 
served that  stimulating  these  bodies  with  an  interrupted  current 
produces  strong  convulsive  movements  of  the  opposite  side  of  the 
body ;  with  a  very  powerful  stimulus  the  whole  side  is  drawn 
into  an  arch.  No  such  effect  could  be  produced  by  stimulating 
the  optic  thalami.  Ferrier  holds ^  that  "in  man  and  the  monkey 
there  is  little,  if  any,  difference  perceptible  between  the  complete 
destruction  of  the  cortical  motor-centres  and  destruction  of  the 
corpus  striatum."  Vivisection  of  this  organ  is  sometimes  followed 
by  hasty  forward  running  motions.  Lesions  of  the  striate  bodies,  in 
the  case  of  the  animals,  are  usually  followed  by  laming  of  the  limbs 
of  the  opposite  side  ;  sometimes,  however,  no  pathological  symp- 
toms result.  As  a  rule,  in  the  case  of  man,  paralysis  of  the  arms 
and  legs  of  the  opposite  side  follows  disease  of  these  organs.  Here, 
as  elsewhere  in  this  region  of  the  nervous  system,  a  certain  sud- 
denness of  the  disturbance  appears  necessary  to  secure  any  marked 
result.  Some  experiments  seem  to  point  to  a  difference  in  the 
effects  of  injury  to  the  two  main  nuclei  of  the  corpora  striata. 
Nothnagel  asserted  that  all  mechanical  injury  to  the  nucleus  len- 
ticularis  of  one  side  results  in  laming  of  the  opposite  side :  destruc- 
tion of  this  nucleus  on  both  sides  brings  the  animal  into  nearly 
the  same  condition  as  the  removal  of  the  cerebral  hemispheres. 
But  voluntary  movements  persisted  after  complete  destruction  of 
both  the  nuclei  caudati  of  the  rabbit. 

'  Comp.  Eckhard  in  Hermann,  Handb.  d.  Physiol.,  II.,  ii.,  p.  125  f. 

^  Lemons  sur  la  Physiologie,  etc.,  p.  659. 

3 Functions  of  the  Brain,  p.  161.  "Ibid.,  p.  349. 


160  THE  BRAIJST   AS   A   CENTRAL   ORGAN. 

There  is  much  evidence,  then,  to  show  that  the  corpora  striata 
are,  as  compared  with  the  optic  thalami,  more  especially  connected 
with  motor  activities.  AVundt  *  considers  them  to  be  pre-eminently 
sio-nificant  as  ganglia  for  the  co-ordination  of  those  motor  impulses 
which  are  derived  from  the  cerebellum  and  the  cerebrum.  The  ' 
relative  importance  which  they  seem  to  have  in  the  higher-,  as  com- 
pared with  the  lower,  animals  (the  monkey  and  man  as  compared 
with  the  rabbit,  etc.)  he  thinks  is  like  that  of  all  the  anterior  por- 
tions of  the  brain  ;  such  portions  are  in  general,  more  significant 
in  man  than  in  the  other  animals.  Wundt's  view  has  considerable 
in  its  support — among  other  things,  the  fact  that,  in  case  of  lesions 
of  the  striate  bodies,  voluntary  motions,  or  those  motions  whose 
motor  innervation  originates  above  these  organs,  seem  to  suffer 
most.  But  we  positively  must  not  adopt  without  qualification  the 
statement  '^  that  the  corpora  striata  are  exclusively  motor,  and  the 
optic  thalami  exclusively  sensory.  In  addition  to  what  has  already 
been  said  (p.  129)  to  caution  one  against  this  view,  it  may  now 
be  added  that  numerous  cases  are  recorded  where  injury,  appar- 
ently confined  to  one  corpus  striatum,  has  resulted  in  loss  of  feeling 
on  the  opposite  side  ;  and  other  cases  where  disease,  apparently 
confined  to  one  optic  thalamus,  has  caused  loss  of  motion  as  well 
as  of  sensation.  Moreover,  the  chief  motor  effects  of  injury  to  the 
striate  bodies  (if  not  all  of  them)  may  be  due  to  the  fact  that  the 
descending  motor  tracts  are  necessarily  involved  in  the  injury, 
rather  than  to  any  special  motor  function  belonging  to  these 
bodies  as  a  central  organ.  Another  theory  of  the  office  of  the 
striate  bodies  rejects  entirely  the  view  which  regards  them  as  in 
any  true  sense  basal  ganglia,  with  either  specially  motor  or  specially 
sensory  functions  ;  and  regards  them  as  belonging  to  the  cerebral 
hemisj)heres,  rather  than  subordinate  to  the  hemispheres  in  func- 
tion.^ But  inasmuch  as  this  theory  has  its  principal  support,  of  a 
physiological  kind,  from  a  single  case  of  an  idiot's  brain,  in  which 
these  bodies  were  of  nearly  normal  size,  while  the  cortex  was  defi- 
cient in  the  motor  regions  and  the  base  of  the  brain  in  general 
small,  it  can  scarcely  be  regar-ded  as  sufficiently  confirmed. 

§  26.  The  researches  of  the  last  few  years  have  tended  to  show 
that  some  S23ecial  relation  exists  between  the  nervous  substance  of 
the  organs  lying  at  the  base  of  the  cerebrum,  and  the  temperature 

'  Physiologische  Psychologie,  i.,  p.  193  f. 

^  As  propounded  by  Carpenter  and  Todd,  and  apparently  adopted  by  Fer- 
rier,  Functions  of  the  Brain,  2.52  f. 

'^  See  A.  Hill,  The  Plan  of  the  Central  Nervous  System,  p.  276  ;  and  Jour- 
nal of  Anat.  and  Physiol.,  July,  1885. 


GKAT   MATTER   OF   THE   THIRD   VElSTTEICLE.  161 

of  the  body.  The  earlier  observations  '  pointed  out  the  limits  be- 
tween the  medulla  oblongata  and  the  pons  as  a  region,  lesion  of 
which  was  followed  by  a  sudden  and  large  rise  of  temperature. 
Still  later,  other  observers  ascribed  vaso-motor  functions  to  the 
optic  thalami,^  or  asserted  the  existence  of  vaso-motor  fibres  in  the 
crura  cerebri  (so  Budge).  In  1884,  J.  Ott  pointed  out  that  cutting 
the  corpora  striata  is  speedily  followed  by  a  marked  rise  of  tem- 
perature. Yet  more  recently  two  experimenters,'  working  together, 
have  arrived  at  certain  conclusions  based  upon  a  large  number  of 
experiments,  chiefly  on  rabbits,  but  also  on  guinea-pigs  and  dogs. 
They  discover  that,  while  the  cortical  substance  can  be  subjected 
to  the  most  severe  and  extended  lesions  without  producing  a  fever- 
ish rise  of  temperature,  puncturiDg  the  brain  at  the  juncture  of  the 
sagittal  and  coronal  sutures,  down  to  the  level  of  the  striate  bodies 
or  deeper,  invariably  j^roduces  a  marked  rise  of  temperature.  If 
the  lesion  only  hits  the  striate  bodies  (especially  the  medial  side, 
near  Nothnagel's  nodus  cursorius)  the  coming-on  of  the  fever  is 
slow  and  gradual ;  but  if  the  needle  is  carried  further  toward  the 
base  of  the  brain,  the  fever  springs  up  at  once  and  reaches  a  max- 
imum in  two  to  four  hours.  In  what  way  these  organs  act  as 
"  fever-centres,"  or  precisely  what  nervous  elements  are  chiefly  in- 
volved in  the  action,  has  not  yet  been  made  clear. 

§  27.  Eckhard  *  is  inclined  to  lay  down  the  law  that  in  all  verte- 
brates the  mechanisms  for  a  change  of  place  lie  rather  in  the  ante- 
rior part  of  this  general  region — corpora  quadrigemina,  etc.;  while 
those  for  maintaining  the  upright  posture  and  the  equipoise  of  the 
body  are  localized  in  the  region  of  the  pons,  cerebellum,  and  me- 
dulla oblongata. 

§  28.  It  should  be  added  that  almost  all  observers  have  hitherto 
failed  to  attach  sufficient  importance  to  the  central  functions  of 
the  gray  matter  which  lines  the  floor  and  walls  of  the  third  ven- 
tricle. Bechterew  ^  has  recently  contributed  the  results  of  very 
important  exiDeriments  to  determine  the  specific  function  of  this 
central  nervous  substance.  He  finds  that  frogs  retain  the  function 
of  balancing  even  when  the  optic  lobes  are  crushed,  if  no  injury  is 
done  to  the  gray  substance  of  the  third  ventricle  or  to  the  crura 

'  By  Tschetscliicliin,  in  Archiv.  f.  Anat.  u.  Physiol.,  1866,  pp.  151  ff. ;  and 
Sclireiber,  Pfliiger's  Archiv.,  viii.,  pp.  576  ff. 

"  Lussana  and  Christiani  (No.  16  of  the  Verhandlungen  d.  physiolog.  Gesell- 
schaft  zu  Berlin,  1883-84). 

^  Ed.  Aronsohn  and  J.  Sachs:  See  Pfliiger's  Archiv.,  xxxvii.  (1885),  ppi 
232  ff. 

^In  Hermann's  Haudb.  d.  Physiol.,  II.,  ii.,  p.  138. 

5  Pfliiger's  Archiv,  xxxi.  (1883),  pp.  479  ff. 
11 


162        THE  BRAIN  AS  A  CENTRAL  ORGAN. 

cerebri ;  they  lose  this  function,  however,  when  a  section  is  made 
into  the  third  ventricle.  Birds  (hens  and  pigeons),  also,  show  the 
same  loss  of  function  when  a  lesion  is  produced  by  running  a  very 
fine  needle  into  the  cavity  of  this  ventricle.  In  the  case  of  dogs, 
Bechterew  considers  himself  able  to  localize  the  function  of  equi- 
poise precisely,  and  to  point  out  the  special  effect  of  injury  done 
to  different  definitely  fixed  localities.  For  example,  bilateral  lesion 
of  the  lateral  or  postero-lateral  parts  of  the  wall  of  the  third  ven- 
tricle results  in  the  impairment  or  loss  of  equipoise  and  co-ordi- 
nated motion  on  both  sides  of  the  body  :  the  lost  function  is  re- 
gained only  after  a  long  time,  and  then  but  partially.  In  none  of 
these  cases  were  any  of  the  phenomena  of  motor  laming  of  the 
extremities  apparent,  or  any  very  marked  disturbance  of  sensation. 
This  gray  matter  of  the  third  ventricle  operates,  Bechterew  thinks, 
in  connection  with  the  olivary  bodies  for  the  co-ordination  of  motor 
impulses  in  response  to  sensations  of  touch,  and  with  the  semi- 
circular canals  in  response  to  sensations  of  sound.  It  is  especially 
important  also  in  equipoise  through  visual  impulse  connected  Avith 
the  changes  in  the  axial  direction  of  the  eyes.  Thus  all  the  above- 
mentioned  organs  operate  with  the  cerebellum  as  complex  and 
correlated  mechanisms  for  keeping  the  body  balanced  in  response 
to  changing  sensory  impulses. 

We  stop  at  this  point  in  our  ascending  review  of  the  automatic 
and  reflex-motor  functions  of  the  central  mechanisms.  For  dis- 
tinctly psycho-physical  and  psychological  questions  the  most  im- 
portant of  the  activities  of  the  nervous  mechanism  still  await  our 
examination ;  these  are  the  activities  of  the  cerebral  hemispheres. 
But  nothing  is  known  as  to  the  molecular  structure  of  these  hemi- 
spheres, or  as  to  their  automatic  and  reflex-motor  centres  and  activ- 
ities, which  adds  anything  of  importance  to  the  description  of  the 
nervous  system  as  a  mechanism,  or  to  the  mechanical  theory  of  its 
action.  It  is  with  such  description  and  theory  that  we  are  now 
concerned.  The  correlations  which  exist  between  the  structural 
condition,  or  j)hysiological  function  of  the  nervous  system,  and  the 
phenomena  of  mind,  are  chiefly  (if  not  wholly)  capable  of  study  as 
illustrated  in  the  cerebral  hemispheres.  But  the  nature  of  the 
nervous  molecular  machiner}',  and  of  its  working  as  mere  machinery, 
is  understood,  as  far  as  our  present  information  will  permit,  by  an 
examination  of  the  physiology  of  the  spinal  cord  and  of  the  inter- 
ci'anial  ganglia  lying  below  the  hemispheres.  As  to  the  alleged 
psychical  functions  of  these  inferior  organs  we  shall  adduce  further 
considerations  when  we  come  to  consider  such  functions  as  belong- 
ing to  the  brain  proper. 


CHAPTER  Y. 

END-OEGANS    OF    THE  NERVOUS  SYSTEM. 

§  1.  In  order  to  understand  the  end-organs  it  is  necessary  to 
refer  again  to  the  place  which  they  hold  in  the  threefold  arrange- 
ment of  the  nervous  mechanism  (compare  Chapter  II.,  §  2).  In  the 
general  division  of  labor  among  its  organs,  certain  cells  situated 
at  the  surface  of  the  body  become  especially  sensitive  to  external 
stimuli.  The  special  function  of  these  cells  accordingly  becomes 
that  of  receiving  the  action  of  such  stimuli,  of  modifying  this  action 
in  accordance  with  their  own  peculiar  structure,  and  thus  of  set- 
ting up  in  the  conducting  nerves  the  neural  process  which  is  prop- 
agated to  the  central  organs.  It  is  obvious,  then,  that  the  struct- 
ure and  grouping  of  the  superficial  cells  must  bear  some  definite 
relation  both  to  the  external  stimulus  and  also  to  the  nerve-fibres 
Avhich  convey  inward  the  nervous  impulse  occasioned  by  it.  The 
end-organs  of  sense  may  then  all  be  described  as  special  adapta- 
tions of  the  superficial  cells  to  the  different  kinds  of  stimuli.  With 
such  special  adaptations  the  peripheral  terminations  of  the  nerve- 
fibres  must  be  connected.  For  the  end-organs,  as  it  were,  look  both 
outward  and  inward.  They  act  as  mediators  between  those  different 
modes  of  external  molecular  motion  which  can  occasion  sensations 
in  us,  and  the  nerves  which  convey  the  results  of  this  motion,  when 
it  has  been  changed  into  a  nerve-commotion,  onward  to  the  central 
organs. 

§  2.  In  the  end-organs  of  the  special  senses  the  fibrils  of  the 
sensory  nerves,  as  a  rule,  terminate  in  cellular  structures  which  have 
the  morphological  significance  of  metamorphosed  epithelial  cells.  The 
end-organs  of  smell  and  taste  show  this  characteristic  development 
most  clearly.  These  end-organs  are,  in  genei-al,  made  up  of  cells 
which,  posteriorly,  pass  into  nerve-threads  that  are  gathered  to- 
gether into  the  sensory  nerve  of  the  special  sense  ;  and  which,  an- 
teriorly, pass  into  conical  or  fusiform  processes.  The  simplest  type 
of  an  end-organ  may  then  be  described  as  follows  :  A  hair-like  pro- 
cess extending  outward,  and  connected  by  a  sensitive  cell  with  a 
nervous  filament  extending  inward.     Such  processes  are  probably 


164  END-OEGANS    OF   SENSE. 

extreinelj'  sensitive  to  external  stimuli  ;  and  perhaps  peculiarly  so 
to  tlie  chemical  changes  which,  at  least  in  the  case  of  three  of  the 
special  senses  (smell,  taste,  and  sight),  are  their  immediate  excit- 
ants. 

All  the  end-organs  of  sense  may  be  regarded  as  modifications  of 
the  type  described  above.  Only  a  small  part,  however,  of  what  are 
ordinarily  called  "  the  organs  of  the  special  senses  "  {e.g.,  the  nose, 
the  mouth,  the  ear,  the  eye,  the  skin)  belongs,  strictly  speaking, 
to  the  nervous  system.  By  far  the  greater  part  consists  of  me- 
chanical contrivances,  designed  to  prepare  the  external  stimuli  and 
conduct  to  the  true  nervous  apparatus  the  impulses  they  occasion. 
These  non-nervous  mechanical  contrivances,  however,  modify  the 
nature  of  the  stimulus  in  so  important  a  manner  as  to  merit  some 
brief  description  in  our  consideration  of  the  nervous  mechanism, 

§  3.  Besides  the  end-organs  of  sense,  histology  points  out  another 
kind  of  terminal  apparatus.  The  efferent  nerves,  in  order  that  they 
may  stimulate  the  muscles,  must  have  some  special  form  of  attach- 
ment to  them.  Special  contrivances  for  connecting  the  motor 
nerves  and  the  muscles  are  actually  discoverable.  We  distinguish, 
then,  two  classes  of  end-organs  :  first,  End-organs  of  Sense,  and, 
second.  End-organs  of  Motion. 

§  4.  Among  the  end-organs  of  sense,  those  of  Smell  have  been 
least  successfully  investigated.  That  portion  of  the  mucous  mem- 
brane of  the  nose  which  clothes  the  upper  region  of  the  nasal  cavity 
and  is  marked  by  a  brown-yellow  color — the  region  of  the  expansion 
of  the  olfactory  nerve — is  called  "  regio  olfactoria ;"  it  contains  the 
end-organs  of  smell.  Here  Ecker  and  Eckhardt  (in  1855)  discovered 
two  different  kinds  of  cells  ;  but  we  are  indebted  to  Max  Schultze  for 
the  first  detailed  description  of  them.  The  epithelial  portion  of  the 
olfactory  organ  is  supposed  to  be  constructed  upon  the  same  type  in 
all  the  vertebrate  animals.  Of  the  two  kinds  of  cells  which  the  last- 
mentioned  investigator  described,  one  is  called  "  epithelial,"  the  other 
"olfactory."  The  epithelial  cells  are  the  larger,  have  an  oval  nucleus 
of  considerable  size,  and  extend  through  the  whole  epithelial  layer. 
Their  external  half  appears  more  or  less  cylindrical  or  columnar  (at 
least  in  the  Triton  and  Proteus),  and  is  described  by  some  observers  ' 
as  striated  longitudinally.  The  form  of  the  inner  half  of  these  cells 
is  varied.  The  olfactory  cells  are  spindle-shaped,  with  a  large, 
round  nucleus,  and  very  long,  fine  processes.  The  external  process 
is  elongated  into  a  stiff  hair,  at  least  in  many  cases,  although 
Schultze  considers  that  in  man  the  olfactory  cells  have  no  cilia. 

'  See  Professor  Babucliin  in  Strieker's  Human  and  Comparative  Histology, 
iii.,  p.  207  f. 


THE   REGIO   OLFACTOEIA. 


165 


These  cells  are  surrounded  by  the  epithelial  cells.  Most  physiol- 
ogists follow  Schultzein  holding  that  the  two  kinds  of  cells  are  dis- 
tinct both  in  form  and  in  function,  and  that  only  the  "  olfactory  " 
cells  are  connected  with  the  end-fibrils  of  the  nerve  of  smell ;  Ex- 
ner '  and  others,  however,  believe  that  the  distinction  is  not  a  fixed 
one.  In  his  opinion  the  structure  of  one  is  merged  into  that  of  the 
other,  and  both  are  connected,  though  in  a  different  manner,  with 
the  subepithelial  net-work  in  which  the  fibres  of  the  olfactory  nerve 
are  lost.  The  exact  histological  relation  of  the  fibrils  of  the  ol- 
factory nerve  to  the  epithelium  of  the  regio 
olfactoria  is  not  yet  made  out.  It  is  probable, 
however,  that  the  finest  of  these  fibrils,  after  pen- 
etrating the  epithelial  layer,  closely  embrace  the 
large  epithelial  cells  and  enter  into  connection 
with  the  inner  extremities  of  the  olfactory  cells. 
According  to  Exner,  the  fibres  of  the  nerve  do 
not  pass  over  directly  into  the  processes  of  the 
end-organ  cells,  but  are  lost  in  a  net-work  whose 
interstices  are  filled  up  with  granules  of  nervous 
matter.  The  first  pair  of  cranial  nerves,  the  ol- 
factorius,  which,  as  we  have  already  seen  on  p.  84, 
is  really  a  lobe  of  the  brain  itself,  is  the  specific 
nerve  of  smell. 

§  5.  The  contrivance  for  applying  the  stimulus 
to  the  end-organs  of  smell  is  very  simple  ;  in  gen- 
eral it  is  only  necessary  that  a  current  of  air,  in 
which  the  stimulating  particles  float,  shall  be  pjg  40 
drawn  through  the  nasal  passages  over  the  mu- 
cous membrane  of  the  regio  olfactoria.  Even  am- 
monia and  camphor,  when  placed  under  the  nos- 
trils, have  no  smell  so  long  as  the  breath  is  held  or  drawn  through 
the  mouth.  In  quiet  inspiration  much  the  greater  part  of  the  cur- 
rent of  air  is  conducted  to  the  pharynx  du-ectly,  and  comparatively 
little  reaches  the  ridge  situated  above  the  nasal  dam  at  the  back  of 
the  nose,  where  the  end-organs  of  smell  are  placed.  In  full  inspir- 
ation, and  still  more  when  short  and  deep  draughts  are  drawn 
through  the  nasal  passages,  a  considerable  amount  of  the  air 
is  forced  over  the  sensory  parts.  By  snuffing  we  increase  the 
amoimt  of  air  drawn  into  the  region  by  first  creating  a  partial  vac- 
uum in  its  cavity.  In  expiration  the  breathing  passage  is  so  located 
as  to  carry  nearly  all  the  air  past  the  sensory  parts  without  striking 
them.  For  this  reason  smelling  is  almost  exclusively  confined  to 
'  Sitzgsber.  d.  Wiener.  Acad.,  Ixiii.,  p.  44  f.  and  Ixv.,  p.  7  f. 


—Olfactory  Cells 
and  Epithelial  Cells 
from  the  Mucous  Mem- 
brane of  the  Nose,  ^""/l 
(After  Schultze.) 


166  END-ORGANS   OF   SENSE. 

inspiration  ;  it  has  been  disputed  whether  the  current  of  expiration 
can  be  smelled  at  all.  But  Debrou  showed  that  the  odor  of  orange 
blossoms,  when  water  tinctured  with  them  has  been  drunk,  can  be 
detected  in  the  expired  air.  The  cui'rent  which  passes  through 
the  anterior  part  of  the  nasal  passages  seems  to  be  the  more  impor- 
tant. This  is  probably  the  reason  why  the  loss  of  the  nose  is  so  fre- 
quently attended  with  loss  of  the  sense  of  smell. 

§  6.  The  end-organs  of  Taste  are  situated  in  certain  papiike, 
found  on  the  upper  surface  of  the  root  of  the  tongue,  on  the  bor- 
ders and  apex  of  the  tongue,  and  in  some  cases  on  the  anterior  por- 
tion of  the  soft  palate.  These  papillae  of  the  tongue,  ave' the  jMpil- 
Ice  circumvallakn  and  the  jMjnUccfungiformes.  The  lateral  portions 
of  the  former  are  pre-eminently  the  regions  of  the  mucous  mem- 
brane of  the  tongue  where  the  end-organs  of  taste  are  found.  The 
same  organs  are  also  found  more  sparsely  distributed  in  the  fungi- 
form papillae.  The  cii'cumvallate  papillae  are  composed  of  connective 
tissue,  which  is  invested  by  a  jDavement  epithelium  arranged  in 
laminae.  The  epithelial  layer  is  thinner  than  elsewhere  at  the  sides  of 
the  papillae,  in  which  the  end-organs  of  taste  (gustatory  flasks  or 
bulbs)  form  a  zone  that  extends  upward  to  about  the  level  at  which 
the  papillae  are  no  longer  protected  by  their  lateral  wall.  In  the 
fungiform  papillae  the  end-organs  api^ear  in  the  epithelium  which 
covers  their  upper  surface,  and  in  the  side  surfaces.  A.  Hoffmann 
also  found  them  in  the  papillae  of  the  region  of  the  soft  palate.  It 
is  more  doubtful  whether  they  exist,  as  has  been  alleged,  on  the  epi- 
glottis. The  papillce  filiformes,  which  are  sometimes  classed  with 
the  two  others,  probably  have  nothing  to  do  with  sensations  of 
taste.' 

Methods  of  experimenting  to  discover  what  surfaces  are  sensitive 
to  taste  arc  not  easily  made  exact,  because  the  stimulus  must  be  in 
solution  to  excite  the  end-oi'gans,  and  because  the  nature  of  the  ex- 
citatory changes  is  chemical.  There  is  scarcely  a  spot  from  the  lips 
to  the  stomach  which  some  physiologist  has  not  described  as  be- 
longing to  the  organ  of  taste.  But  the  regions  where  the  above- 
described  papillae,  with  their  gustatory  flasks,  are  found,  are  doubt- 
less the  principal — and  probably  they  are  the  only — sensitive 
surfaces.  Considerable  differences  exist,  however,  among  different 
species  of  animals,  and  even  among  different  individual  men — es- 
pecially as  to  the  sensitiveness  of  the  tip  and  edges  of  the  tongue, 
and  of  the  anterior  surface  of  the  palate.  All  the  evidence  tends  to 
show  that  the  gustatory  flasks  are  the  sole  end-organs  of  taste. 

'  Comp.  Briicke,  Vorlesungen  iiber  Pliysiologie,  ii.,  p.  257;  and  von 
Vintscligau  in  Heimauu  s  Handb.  d.  Plijsiol. ,  III.,  ii.,  p.  147. 


THE   GUSTATORY   CELLS. 


167 


Fig  41. — Giistatoi-y  Bulbs  from  the  Lateral  Gustatory 
Organ  of  the  Kabbit.     ^=%.     (Engelmann.) 


§  7.  The  microscopic  structure  of  tlie  end-organs  of  taste  is  de- 
scribed in  substantially  the  same  way  by  all  investigators,  al- 
though these  structui-es  vary 
considerably,  according  to 
their  position,  and  accord- 
ing to  the  different  species 
of  animals.  In  general  they 
are  like  a  glass  knob  with  a 
short  neck,  and  with  its 
length  somewhat  greater 
than  its  greatest  width. 
Hence  they  are  called" gus- 
tatorij  knobs"  or  "bulbs" 
(so  Henle),  or,  better,  "  gus- 
tatory  flasks  "  (so  M.  Schultze).  They  occupy  flask-shaped  cavities 
of  the  epithelium,  which  they  completely  fill.     Their  lower  or  inner 

part  rests  on  the  connective 
tissue  of  the  mucous  mem- 
brane ;  theu'  upper  and  more 
slender  part  is  sun'ounded  by 
epithelial  cells  and  has  an 
opening,  or  pore,  of  from  ^jqVb" 
to  ysVo  '^f  ^^  inch  in  diameter, 
at  the  surface  of  the  epithe- 
lium. The  margin  of  this  pore 
is  usually  formed  by  placing 
several  cells  together,  but 
sometimes  by  a  single  cell  which  appears  perforated  with  a  round 
hole.  Each  of  the  gustatory  flasks  consists  of  from  fifteen  to  thirty 
long,  thin  cells,  arranged  like  the  leaves  of  a  bud  in  closely  com- 
pressed rows  around  the  axis. 

All  the  gustatory  flasks  are  comjjosed  of  two  kinds  of  cells  : 
some  are,  essentially,  epithelial  cells,  and  have  probably  no  direct 
connection  with  the  nerves ;  the  others  are  highly  differentiated 
structures,  are  probably  directly  continuous  with  the  nerve-fibrils 
and  are  thought  to  be  true  gustatory  cells.  The  epithelial  or  iu- 
vesting-cells  are  long,  narrow,  spindle-shaped,  bent,  with  a  nucleus 
well  marked  ;  the  outward  end  is  pointed,  the  central  end  branch- 
ing. The  gustatory  cells  are  thin,  long,  and  highly  refractive  of 
light,  with  nearly  the  whole  body  of  the  structure  occupied  by  an 
elliptical  nucleus.  The  body  of  the  cell  is  elongated  into  two  pro- 
cesses, of  which  the  upper  or  peripheral  is  tolerably  broad  and 
bears  a  short  and  fine  point  like  a  hair  or  pencil-point.     This  point 


Fig.  49. — Transverse  Section  through  a  Papilla 
Circumvallata  of  a  Calf.  Showing  the  arrange- 
ment and  distribution  of  the  gustatory  buib. 
2^/j.     (Engelmann.) 


168 


END-ORGANS   OF   TASTE. 


lies  in  a  canal,  in  the  epithelial  layer,  and  rarely  projects  from  the 
pore  of  the  flask.  The  lower  or  central  process  of  the  cell  is  much 
attenuated,  and  usually  divides  into  two  branches.     A  direct  con- 


Fis.  43. — Isolatecl  Gustatory- 
Bulb,  from  the  Lateral 
Gustatory  Organ  of  the 
Kabbit.  ^""/j.  (Engelmann.) 


Fig.  44.— a.  Isolated  Gustatory  Cells,  from  the  Lateral 
Organ  of  the  R.abbit ;  6,  an  Investing  and  Two  Gusta- 
tory Cells,  isolated  but  still  in  connection,  ^""/i.  (En- 
gelmann.) 


nection  of  these  processes  with  the  fibrils  of  the  gustatory  nerve  is 
assumed  by  all  investigators.  The  manner  in  which  the  nerve-fibres 
terminate  within  the  papillae  is  different  in  different  animals. 

The  gloaso-pharyngeal  nerve  is  the  principal  nerve  of  taste.  It  is 
distributed  to  the  back  of  the  tongue,  enters  the  circumvallate  pa- 
pillae, where  it  forms  a  minute  plexus,  interspersed  with  nerve-cells, 
from  which  both  meduUated  and  non-medullated  fibres  pass  to  the 
base  of  the  gustatory  flasks.  The  lingual  branch  of  the  trigeminus 
has  also  some  claims  to  be,  in  a  minor  degree,  a  nerve  .of  taste. 
Sehiff  '  considers  it  as  designed  for  sour  taste,  with  a  slight  sensi- 
tiveness to  bitter  also. 

§  8.  In  considering  the  end-organs  of  Touch,  attention  should 
be  directed  to  the  great  variety  of  sensations  which  are  grouped 
together  under  the  word  "touch,"  in  the  broadest  meaning  appli- 
cable to  it.  The  question  is  thus  raised  whether  any  histological 
difference  is  to  be  detected  in  the  nervous  apparatus  which  may 
serve  as  a  physical  basis  for  the  difference  in  the  sensations.  We 
may  set  aside  for  the  present  all  consideration  of  the  feelings  of 
pain,  of  exertion  and  fatigue,  and  the  so-called  "  common  feeling  " 
and  "muscular  sense."  The  question  is  thus  reduced  to  this  nar- 
row form  :  Can  histology  point  out  two  specifically  distinct  kinds  of 
end-organs  in  the  skin,  one  of  which  serves  for  sensations  of  tem- 
perature, and  the  other  for  sensations  of  pressure  ? 

§  9.  Histological  examination  shows  that  the  sensory  nerves  dis- 
tributed to  the  skin — the  general  organ  of  touch — terminate  in  two 

'  Molesch.  Unters..  X.,  p.  406  f.,  as  referred  toby  von  Vintschgau  in  Her* 
mann's  Haudb.  d.  Physiol.,  III.,  ii.,  p.  171  f. 


THE   TACTILE   CORPUSCLES. 


169 


ways,  either  in  free  end-fibrils  or  in  special  constructions  called 
"tactile  corpuscles"  or  "end-bulbs."  The  different  varieties/ all, 
however,  essentially  alike,  of  these  special  end-organs  of  touch  have 
been  named  after  as  many  different  investigators.  Their  general 
office  is  that  of  modifying  and  multiplying  the  effect  of  the  stimu- 
lus upon  the  nerve-fibres  which  terminate  in  them.  The  so-called 
"  corpuscles  of  Pacini "  were  the  fii'st  end-apparatus  to  be  discovered 
in  connection  with  the  peripheral  termination  of  the  sensory  nerves  ; 
they  were  seen  more  than  one  hundred  and  fifty  years  ago  by  Vater. 
In  man  they  are  constantly  present  in  the  subcutaneous  connective 
tissue  of  the  palms  of  the  hand  and  of 
the  soles  of  the  feet ;  but  are  most 
numerous  in  the  palmar  surfaces  of 
the  fingers  and  toes,  especially  the 
third  phalanges,  although  they  occur 
in  the  neck,  arms,  etc.  In  some  places 
they  are  visible  to  the  naked  eye  as  a 
minute  gTain  of  from  -^^  to  i  of  an 
inch  in  diameter.  They  may  be  said 
to  be  nothing  more  than  the  ends  of 
medullated  nerve-fibres  remarkably 
thickened.^  Each  corpuscle  consists 
of  layers  of  connective  tissue,  arranged 
concentrically  and  more  closely  packed 
near  the  centre  ;  these  surround  a  cav- 
ity containing  a  soft  nucleated  mate- 
rial, into  the  interior  of  which  the 
nerve  penetrates.  Here  the  nerve- 
fibre,  having  become  a  naked  axis-cyl- 
inder, appears  to  terminate  in  a  little 
bulb.  Examination  with  the  highest 
powers  of  the  microscope  shows  that  the  axis-cylinder  of  the  fibre 
is  fibrillated,  and  that  the  terminal  bulb  consists  of  finely  granular 
substance. 

Closely  allied  to  the  foregoing  structures  are  the  so-called  "  end- 
bulbs  of  Krause."  These  are  small  capsules  of  connective  tissue  in 
which  nuclei  can  be  detected.  In  them  the  nerve-fibrils  of  touch 
terminate  either  in  a  coiled  mass  or  in  a  bulbous  extremity.  They 
are  from  ^^-^  to  yoVo  ^^  ^^  inch  in  diameter,  and  exist  in  the  con- 

'  On  the  different  kinds  of  terminal  corpuscles,  a  principal  monograph  is  by 
Fr.  Merkel,  Ueber  die  Endigungen  der  sensibleu  Nerven  in  der  Haut  der 
Wirbelthiere,  Rostok,  1880. 

'^  So  Biesiadecki  in  Strieker's  Human  and  Comparative  Anatomy,  ii.,  p.  232. 


Fig.  45. — Corj^iuscle  of  Pacini  (or  Vater) 
from  the  Mesentery  of  the  Cat,  (After 
Frey. )  a,  nerve  with  its  sheaths ;  6, 
system  of  tunics  constituting  the  cap- 
sule of  the  corpuscle  ;  f,  axial  canal, 
in  which  the  nerve-tibre  ends. 


170 


END-ORGANS   OF   SENSE. 


Fig.  46. — End-bulbs  from  the 
Conjunctivfi  of  the  Human 
Eye.  (After  KoUiker.)  1, 
has  two  nerve-fibres  which 
form  a  coil  within  the  end- 
bulb  ;  2,  has  a  fatty  core. 
The  nerve-fibre  of  3  ends 
within  in  the  form  of  a  knot. 


junctiva  of  the  eye,  in  the  tongue,  the  Hps,  the  floor  of  the  buccal 
cavity,  etc.  The  "  corpuscles  of  Wagner  "  (or  Meissner,  -who  has 
furnished  most  of  the  details)  may  be  described  as  oval-shaped 
bodies,  made  up  of  superimposed  laminae  and 
bearing  some  resemblance  to  a  miniature  fir- 
cone. The  medullated  nerve-fibres,  like 
"  creeping  roots,"  wind  beneath  the  cutane- 
ous papillse,  and  here  and  there  penetrating 
them,  terminate  in  the  corpuscles.  Within 
the  corpuscles, 
according  to 
Kolliker,  the 
fibrils  form  two 
or  three  coils, 
and  finally  join 
together  in 
loops.  These 
tactile  end-organs  are  most  constant 
and  numerous  in  the  terminal  pha- 
langes of  the  fingers;  they  occur  in 
smaller  numbers  on  the  palm  and 
back  of  the  hand,  on  the  sole  and 
back  of  the  foot,  and  sometimes  on 
the  nipple,  lips,  etc.  They  are  seated 
in  the  papillse  of  the  skin.  Meissner 
counted  four  hundred  papillse  in  -^V 
of  an  inch  square  on  the  third  pha- 
lanx of  the  index-finger,  and  found 
these  corpuscles  in  one  hundred  and  eight  of  them.  Their  long 
diameter  lies  in  the  direction  of  the  papillse  and  extends  from  -g^-g^ 
to  Yj-Q  ^^  ^^  ^^^^  »  ^^®y  ^^'®  about  -g-J-jj-  of  an  inch  in  thickness. 

§  10.  Since  the  surface  of  the  skin  is  in  general  sensitive  to  press- 
ure and  to  temperature,  it  follows  that  the  special  structures  de- 
scribed above  as  occurring  in  parts  of  this  surface,  cannot  be  the 
sole  end-organs  of  touch.  Modern  histology  has  demonstrated 
the  presence  of  an  intricate  plexus  of  non-meduUated  nerve-fibres 
which  end  in  free  extremities  between  the  cells  of  the  mucous 
layer.  This  terminal  plexus  of  nerve-fibres  is  also  the  end-organ 
of  so-called  general  sensibility  and  of  touch. 

None  of  the  attempts  hitherto  made  to  establish  specific  relations 
between  the  varieties  in  the  structure  of  the  tactile  end-organs  and 
the  varieties  of  the  sensations  which  they  administer  can  be  joro- 
nounced  successful.     Ivrause  has  tried  to  deduce  from  the  coustruc- 


tG.  47.  —Corpuscles  of  Touch.  (After 
Frey.)  a,  from  the  soft  skin  of  the 
duck's  bill ;  b  and  c,  from  the  papillse 
of  the  tongue  of  the  same  animal. 


THE   TACTILE   COEPUSCLES.  171 

tion  of  the  corpuscles  of  Pacini  their  fitness  to  act  as  the  end- 
organs  of  pressure  ;  but  these  corpuscles  are  wanting  in  many 
parts  of  the  body  that  are  sensitive  to  pressure.  Wagner  con- 
sidered the  corpuscles  which  bear  his  name  to  be  special  organs  of 
touch.  But  it  has  been  shown  by  Merkel  that  these  corpuscles  are 
nothing  but  aggregates  of  more  elementary  forms,  the  so-called 
"  tactile  cells."  Some  have  argued  that  the  end-bulbs  of  Krause  and 
the  corpuscles  of  Pacini  are  the  organs  of  general  feeling  {sensus 
communis)  ;  but  others,  with  more  probabihty,  assign  this  function 
to  the  free  nerve-endings  ;  while  Merkel  is  of  opinion  that  the  latter 
are  specifically  concerned  in  sensations  of  temperature.  Nothing 
is  known  on  this  point  beyond  the  fact  that  the  skin,  within  which 
the  sensory  nerve-fibres  terminate,  either  in  free  ends  or  in  special 
tactile  corpuscles,  is  the  organ  for  all  the  varieties  of  sensation 
brought  under  the  most  general  meaning  of  the  word  "  touch." 

The  more  precise  manner  in  which  the  terminal  fibres  of  the 
nerves  of  touch  stand  related  to  the  individual  tactile  cells  is  also 
still  in  doubt.  Some  investigators  consider  that  the  fibres  enter 
into  the  very  protoplasm  of  the  cells  (Merkel,  Frey)  ;  others  that 
they  spread  themselves  on  end-plates  superimposed  on  the  cells 
(Retzius,  Ranvier). 

§  11.  With  the  exception  perhaps  of  the  ear,  the  Eye  is  by  far 
the  most  elaborate  and  comphcated  of  the  end-organs  of  sense. 
This  is  true  of  those  portions  of  it  which  are  designed  merely  to 
bring  the  external  stimulus  to  bear  upon  the  nervous  structure,  as 
well  as  of  this  structure  itself.  Considering  it  as  a  whole,  we 
may  say  that  the  peripheral  organ  of  sensations  of  light  and  color 
is  an  optical  instrument  constructed  on  the  plan  of  a  water  camera 
obscura,  with  a  self-adjusting  lens,  and  a  concave,  sensitive,  nervous 
membrane  as  a  screen  on  which  the  image  is  formed. 

§  12.  The  eyeball  consists  of  three  coats  or  tunics  inclosing 
three  translucent  refracting  media.  Since,  however,  the  front  part 
of  the  outer  one  of  these  coats  is  itself  translucent  and  refracting, 
the  number  of  refracting  media  in  the  eye  is  really  four.  (1)  The 
first  or  external  coat  consists  of  two  parts  :  (a)  the  Sclerotic  or 
posterior  five-sixths  part  ("white  of  the  eye"),  which  is  a  firm, 
fibrous  membrane  formed  of  connective  tissue  intermingled  with 
elastic  fibres  ;  and  (b)  the  Cornea,  or  translucent  anterior  one-sixth 
part,  which  is  circular  and  convex  in  form,  and  covered  with  con- 
junctival epithelium.  The  cornea  rises  and  bulges  in  the  middle 
like  a  watch-glass.  (2)  The  second  coat,  or  tunic  of  the  eye,  also 
consists  of  two  parts  :  these  are  (a)  the  Choroid  coat,  which  com- 
prises much  its  larger  portion,  is  of  a  dark  brown  color,  due  to  ita 


172 


THE   HUMAlSr   EYE. 


pigment  cells  (except  in  the  case  of  albinos),  and  is  abundantl;f 
provided  with  nerves  and  blood-vessels  ;  and  (b)  the  Iris,  a  circular, 
flattened,  disk-shaped  diaphragm  in  front  of  the  lens  (the  colored 
part  of  the  visible  eyeball),  bathed  with  aqueous  humor,  and  hav- 
ing in  its  centre  a  circular  aperture  called  the  ' '  pupil "'  of  the  eye. 
The  anterior  border  [corpus  ciliare)  around  the  iris  consists  of  the 


JPi:  ci% 


ScJffj: 


PiQ.  48. 


-Het. 

■CJior. 

-Horizontal  Section  through  the  Left  Bye.     ^/j.     (Schematic,  from  Gegenbaur.) 


ciliary  muscle  and  the  ciliary  processes.  (3)  The  Retina  is  the 
third  or  inner  coat  of  the  eye.  It  is  a  delicate  membrane  of  ex- 
quisite ti'ansparency  and  almost  perfect  optical  homogeneity  ;  it 
has  a  highly  comj)lex  structure,  consisting  of  nine  or  ten  layers,  th^ 
truly  nervous  portions  of  which  contain  nerve-fibres,  nerve-cells, 
and  special  end-organs,  together  with  connective  tissue  and  blood- 
vessels.    The  inner  surface  of  the  retina  is  moulded  on  the  vitreous 


THE   FOUR   EEFRACTING   MEDIA.  173 

body,  and  it  extends  from  the  entrance  of  the  optic  nerve  nearly 
as  far  forward  as  the  ciHary  processes. 

§  13.  The  eyeball  has  four  translucent  refracting  media.  The 
first  of  these — enumerating  inward  from  the  outside  front — is  (1) 
the  Cornea,  already  spoken  of  as  the  anterior  one-sixth  of  the 
outer  coat  of  the  eye.  (2)  The  Aqueous  Humor  fills  the  space 
between  the  cornea  and  the  lens,  and  is  divided  by  the  iris  into 
two  chambers,  of  which  the  front  one  is  much  the  larger.  It  is 
limpid  and  watery  ;  it  holds  in  solution  the  salts  of  the  blood- 
serum,  with  traces  of  organic  substances.  (3)  The  Crystalline  Lens 
is  situated  between  the  iris  and  the  vitreous  body.  It  is  a  transpar- 
ent biconvex  lens,  with  its  antero-posterior  diameter  about  one-third 
less  than  the  transverse  diameter.  It  consists  of  a  capsule  and  in- 
closed body.  It  is  of  "  buttery  consistency,"  composed,  like  an 
onion,  of  a  number  of  easily  separable  layers.  Each  layer  consists 
of  fibres  which,  within  the  layer  are,  as  a  rule,  radial.  Between 
the  entire  ciliary  part  of  the  retina  and  the  corresponding  part  of 
the  vitreous  humor  is  interposed  a  structureless  membranous  body, 
to  which  the  edge  of  the  lens  is  attached,  and  which  radiates  out- 
ward and  maintains  the  lens  in  tension.  It  is  called  the  suiipen- 
sory  ligament,  (or  Zonula  of  Zinn)  and  its  office  is  very  important 
in  the  accommodating  of  the  eye  to  different  distances.  (1)  The 
Vitreous  Humor  consists  of  a  number  of  firm  sheets  or  layers 
(lamellae),  between  which  fluid  is  contained,  built  iuto  a  body  that 
is,  optically  considered,  transparent  and  homogeneous.  It  occupies 
most  of  the  space  inclosed  by  the  tunics  of  the  eye.  It  is  thought 
to  be  a  gelatinous  form  of  connective  tissue,  and  is  composed  most- 
ly of  water  with  salts  in  solution,  of  proteids  and  mucin,  fats  and 
extractive  matters — especially  urea.  Its  peculiar  structure  is  of 
little  significance  for  the  physiology  of  the  eye. 

§  14.  Of  the  appendages  or  accessory  parts  of  the  eye — such  as 
the  eyebrows,  the  eyelids,  lachrymal  apparatus,  muscles  of  the  eye-' 
ball — only  the  mechanism  by  which  the  eye  is  moved  in  its  or- 
bit has  any  special  significance  for  physiological  psychology. 
The  building-up  of  a  world  of  visible  objects,  and  even  the  forma- 
tion of  a  so-called  "  field  of  vision,"  is  dependent  upon  the  great 
mobility  of  the  eye.  The  eyeball  is  moved  in  its  bony  socket, 
where  it  is  embedded  in  a  mass  of  fat  as  in  a  socket-joint,  by  sis 
muscles,  which  are  attached  to  it  somewhat  like  the  bridle  to  the 
horse's  head.  Four  of  these  muscles  spring  from  the  bony  wall 
near  the  point  where  the  optic  nerve  enters,  extend  through  the 
length  of  the  socket  and  pass  directly  to  the  eyeball,  where  they 
are  attached  to  it,  one  above,  one  below,  one  on  the  outer,  and  one 


]74 


THE  HUMAlSr  EYE. 


on  the  inner  side,  (the  recti;  intemiis  and  externus,  superior  andinfe* 
rior).  In  moving  both  eyes  up  or  down,  the  same  muscles  in  both 
contract  simultaneously  ;  in  moving  the  eyes  to  the  right,  the  outer 


Fig.  49. — Muscles  of  the  Left  Human  Eye, 
seen  from  above,  rs,  rectus  superior  ; 
re,  i-ectus  externns  ;  and  rit,  rectus 
internus  ;  os,  superior  oblique,  with 
its  tendon,  t,  which  runs  through  the 
fnembranous  pulley,  ?«,  at  the  inner 
wall  of  the  cavity  of  the  eyeball. 


Fig.  50. — Muscles  of  the  Left  Human  Eye,  seen 
from  the  outside.  Ir,  levator  of  the  upper  eye- 
lid, which  covers  the  rectus  superior,  rs,  re,  os, 
as  in  the  preceding  figure ;  rif,  rectus  inferior ; 
oi,  inferior  oblique. 


muscle  of  the  right  eye  and  the  inner  of  the  left,  contract  simul- 
taneously (and  mce  versa)  ;  in  turning  both  eyes  inv^ard  to  converge 
them  upon  a  near  object,  the  two  inner  muscles  contract  together. 
We  cannot  move  the  eyes  so  that  the  optical  axes  do  not  either 
meet  or  remain  parallel ;  we  cannot  look  with  one  eye  upward  and 
the  other  downward,  nor  with  one  eye  to  the  left  and  the  other  to 
the  right ;  nor  can  we  voluntarily  turn  the  eyes  farther  apart  than 
when  their  axes  are  parallel. 

The  other  two  of  the  six  muscles  of  the  eye  are  called  oblique.  Of 
these  one  is  superior  and  internal ;  it  does  not  pass  directly  forward 
from  its  place  of  origin,  at  the  posterior  aperture  through  which 
the  optic  nerve  enters  to  the  eye,  but  first  runs  through  a  ring,  then 
turns  around,  and  is  attached  obliquely  to  the  upper  surface  of  the 
eyeball.  The  other  oblique  muscle  begins  at  the  inner  wall  in  the 
socket,  passes  under  the  eye-ball,  and  is  attached  to  it  opposite  to 
the  superior  oblique  muscle.  The  two  oblique  muscles  combine 
with  the  four  recti  to  move  the  eyes  in  various  directions  which 
would  be  impossible  for  the  latter  alone. 

§  15.  The  problem  which  is  to  be  solved  by  the  end-organ  of 
vision  may  be  stated  in  a  general  form  as  follows  :  A  mosaic  of 
localized  sensations  must  be  so  constructed  that  changes  in  the 
quantity,  quality,  local  relation,  and  sequence  of  these  sensations 


THE  FOEMING  OF  THE  IMAGE.  175 

shall  be  quickly  interpreted  as  indicative  of  the  size,  shape,  lo- 
cality, and  motion  of  external  visible  objects.  The  most  important 
part  of  the  solution  of  this  problem  falls  tipon  the  nervous  struct- 
ure of  the  retina.  It  is  itself  a  mosaic  of  nervous  elements,  the 
excitation  of  which  may  vary  in  quality,  quantity,  local  coloring, 
and  sequence  of  the  different  elements  excited.  But  in  order  that 
the  retina  may  exercise  its  function  with  the  precision  and  delicacy 
of  detail  for  which  its  structure  fits  it,  the  rays  of  light  reflected 
from  a  single  point  of  the  surface  of  the  visible  object  must  excite  a 
single  one,  or  at  most  a  small  and  definite  group,  of  the  retinal 
nervous  elements.  The  sensations  thus  occasioned  can  then  un- 
dergo a  systematic  arrangement  by  the  mind.  It  is  the  work  of 
the  translucent  refracting  media  of  the  eye  to  apply  the  stimulus  to 
retinal  elements  exactly  discriminated,  and  in  an  order  correspond- 
ing to  the  object  ;  that  is  to  say,  the  cornea,  the  humors  of  the  eye, 
and  the  lens  must  form  an  image  on  the  retina.  To  show  the  pos- 
sibility of  this  by  calculating  how  the  general  laws  of  optics  apply 
to  the  special  structure  of  the  eye,  as  anatomy  describes  it,  and  to 
make  the  calculations  accord  approximately  with  the  facts,  has  been 
the  labor  of  a  number  of  investigators,  especially  of  Helmholtz  and 
his  pupils.  To  the  results  of  this  labor  only  a  brief  allusion  must 
suffice. 

§  16.  The  four  media  of  the  eye  constitute  a  system  of  refracting 
surfaces,  each  of  which  is  separated  from  the  one  adjoining  by  a 
circular  cut,  as  it  were,  in  the  whole  refraction -substance.  Espe- 
cially is  this  true  of  the  lens  with  its  concentric  layers.  The  "  image  " 
formed  upon  the  first  member  of  this  system  of  surfaces,  by  its  re- 
fraction of  such  bundles  of  rays,  from  the  object,  as  all  lie  in  a  plane 
at  right  angles  to  the  axis  of  the  system,  thus  becomes  an  "  object  '' 
for  the  second  refracting  surface  of  the  system  ;  and  the  image- 
formed  by  the  second  an  object  for  the  third  ;  and  so  on.  The  re- 
sult of  any  number  of  such  refractions  will  accordingly  always  be 
an  image  whose  points  lie  in  a  plane  at  right  angles  to  the  axis  of 
the  system  of  refracting  surfaces,  and  which,  as  a  whole,  is  in  true 
perspective  to  the  original  object.  The  last  image  and  the  object 
are  geometrically  similar. 

In  tracing  the  course  of  the  rays  of  light  through  the  refracting 
media  of  the  eye,  two  things  must  be  taken  into  the  account :  (1) 
the  indices  of  refraction  of  these  media,  and  (2)  the  geometrical 
form  and  position  of  all  the  limiting  surfaces.  (1)  The  means  for 
attaining  a  knoAvledge  of  the  former  is  by  taking  the  average  result 
of  an  examination  of  a  number  of  eyes  supposed  to  be  normal 
Fortunately  for  science,  death  has,  for  the  first  twenty-foiir  hours, 


176 


THE   HUMAN   EYE. 


little  or  no  effect  in  changing  the  indices  of  refraction  of  the  eys. 
Krause  '  found  the  mean  index  of  refraction  of  the  cornea  to  be  =: 
1.3507,  of  the  aqueous  humor  =  1.3420,  of  the  vitreous  body  = 


Fig.  51. — Median  Section  through  the  Axis  of  the  Lens  of  the  Bye.    (Schematic,  after  Babuchin.J 

1.3485.  But  Helmholtz  (subsequent  observers  have  agreed  better 
with  his  result  than  with  Krause's)  found  the  two  latter  indices  of 
refraction  to  be  =  1.3365  and  i=  1.3382, 
respectively.  The  lens  of  the  eye,  espec- 
ially, is  not  homogeneous  throughout  as 
to  its  index  of  refraction.  Each  layer  has 
its  own  index,  and  the  amount  of  the 
index  of  each  layer  increases  regularly 
toward  the  kernel  of  the  lens.  The  work 
of  refraction  done  by  the  lens  is,  there- 
fore, greater  even  than  that  which  could 
be  done  by  a  homogeneous  lens  with  an 
index  of  refraction  equal  to  that  of  the 
kernel,  or  most  highly  refracting  part  of 
the  lens. 

(2)  The  position  and  form  of  the  separating  surfaces  of  the  re- 
fracting media  can  be  only  approximately  determined  in  the  living 
eye.  Three  of  these  surfaces  are  of  chief  importance — the  anterior 
surface  of  the  cornea,  and  the  anterior  and  posterior  surfaces  of  the 
lens.  The  convexity  of  the  first  of  these  three  is  found  to  depart 
perceptibly  from  a  sphere  ;  it  is  greater  toward  its  edge  than  at  its 
vertex,  where  it  resembles  rather  a  section  of  an  ellipsoid.  The 
advantage  of  such  a  shape  is  seen  in  the  fact  that  the  images 

'  Krause's  experiments  refer  to  rays  of  the  wave-length  to  which  the  bright- 
est place  in  the  solar  spectrum  corresponds ;  that  is,  to  the  place  at  the  end  of 
the  first  third,  or  quarter  between  D  and  E.  The  refraction-index  of  water  for 
these  rays  he  assumed  at  =1.33424. 


Fig.   52. — View  of    the  Lens 
Profile.     Vi-     (After  Arnold.) 


THE   PROCESS    OF   ACCOMMODATIOlSr.  177 

formed  when  the  pupil  is  expanded  are  thus  made  sharper  than 
they  could  otherwise  be.  No  observable  refraction  takes  place  on 
the  posterior  surface  of  the  cornea,  because  the  difference  between 
the  indices  of  refraction  of  the  cornea  and  of  the  aqueous  humor  is 
so  slight  that  the  faint  images  from  this  surface  vanish  by  proxim- 
ity to  the  stronger  ones  refracted  from  the  front  part  of  the  cornea. 

§  17.  The  power  of  altering  the  refracting  conditions  of  the  eye, 
so  as  to  enable  the  media  to  form  a  single  perfect  image  on  the 
retina,  for  varying  distances  of  the  object,  is  called  its  power  of 
"  accommodation  "  or  adjustment.  Plainly  such  adjustment  of  the 
eye  cannot  take  place,  like  that  of  a  camera  obscura,  by  changiuo- 
to  any  appreciable  extent  the  distance  of  the  lens  from  the  screen 
on  which  the  image  is  formed.  It  must  therefore  take  place,  either 
by  increasing  the  indices  of  refraction  of  the  media  of  the  eye,  or 
by  increasing  the  curvature  of  one  or  more  of  the  refracting  surfaces. 
It  is  now  known  to  be  due  to  changes  in  the  convexity  of  the  lens, 
principally,  if  not  wholly,  of  its  anterioi-  surface.  The  posterior 
apex  of  the  lens  remains  unmoved.  There  are  several  methods  of 
experiment  which  demonstrate  that  in  accommodation  for  near  dis- 
tances the  front  of  the  lens  becomes  more  strongly  arched.  When 
accommodation  is  taking  j)lace,  the  pupil  may  be  seen  not  only  to 
contract,  but  also  to  draw  its  edge  forward.  Helmholtz  calculated 
the  amount  of  this  forward  movenient  for  two  cases  at  about  J^y  and 
-gJg  of  an  inch,  respectively.  Moreover,  by  an  ingenious  contrivance 
the  image  reflected  from  the  anterior  surface  of  the  lens  may  be 
watched  as  it  becomes  smaller  and  more  distinct  on  adjustment 
for  near  distances,  thus  showing  that  the  surface  from  which  it  is 
reflected  has  increased  its  curvature. 

It  is  obvious  that  the  mechanism  for  adjusting  the  eye  must  be 
under  the  brain's  control,  since  adjustment  is  voluntary  ;  and  that 
it  must  consist  of  muscles  which  lie  within  the  eyeball.  The  ac- 
cepted hj-pothesis  concerning  the  nature  and  action  of  this  mechan- 
ism was  first  proposed  by  Helmholtz.  This  investigator  assumes 
that  the  lens,  when  the  eye  is  at  rest,  does  not  have  the  form  which 
corresponds  to  a  condition  of  equilibrium  in  its  own  elastic  power. 
If  it  were  not  held  in  by  its  surroundings,  it  would  be  more  arched 
than  it  is  both  before  and  behind.  But  it  is  kept  flattened  by  the 
radial  tension  of  the  susjjenso7-i/  ligament  ;  when  this  tension  is  with- 
drawn the  lens  becomes  curved  by  the  action  of  its  own  elasticity. 
The  withdrawal  of  the  tension  is  accomplished  by  the  action  of  the 
ciliary  muscle,  the  fibres  of  which  have  their  point  of  fixation  at  the 
edge  of  the  cornea,  and  run  from  here  in  the  direction  of  a  merid- 
ian toward  the  equator  o  fthe  eye.  When  the  ciliary  muscle  cou- 
12 


178 


THE   HUMAN    EYE. 


tracts,  the  free  ends  of  its  fibres  are  drawn  toward  its  fixed  ends 
on  the  edge  of  the  cornea  ;  the  radial  tension  of  the  suspensory  hg- 
ament  is  thus  relaxed,  and  the  lens  is  allowed  to  assume  its  natural 
form  under  the  equipoise  of  its  own  elastic  forces. 


Conjumfiva 
cprneae 


fun.  Sciuemmii 
Jiiy.  Jiect.  iridis 


Coiijnnclivn 
sclerac 


Fig.  53. 


Proc.  ciliarix 


railiarer  circulurev 

Ciliarmvslcel 

-Sectional  View  of  the  Connections  of  the  Cornea,  Ciliary  Muscle,  Ciliary  Processes,  etc. 
'"/j.     (Gegenbaur.) 


The  occulo-motor  nerve  furnishes  the  fibres  that  serve  the  ciliary 
muscle  ;  these  fibres  run  in  the  posterior  strands  of  its  roots.  Their 
central  place  of  origin  is  in  the  posterior  part  of  the  floor  of  the 
third  ventricle  ;  stimulating  the  front  division  of  this  part  produces 
accommodation  of  the  lens  ;  stimulating  the  back  division  of  the 
same  part  produces  contraction  of  the  pupils.  Stimulation  still 
further  back,  where  the  third  ventricle  passes  into  the  aqueduct  of 
Sylvius,  produces  contraction  of  the  internal  rectus  muscle  of  the 
eye  ;  and  the  innervation  of  this  muscle  is,  of  course,  regularly  con- 
nected with  adjustment  for  near  distances.  Thus  all  the  mechan- 
ism of  accommodation,  both  that  of  the  central  organs  and  that  of 
the  end-organs,  is  made  to  work  together  for  the  production  of  an 
image  upon  the  retina. 

§  18.  Given  the  formation  of  the  image  upon  the  retina,  it  is  fur- 
ther required  in  order  to  vision  that  this  physical  process  should 
be  changed  into  a  physiological  process.  We  now  examine  briefly 
the  mechanism  by  which  such  a  change  is  accomplished.  [The 
reader  is  referred  to  the  larger  specific  treatises  for  the  detailed 
theory  of  the  schematic,  the  emmetropic,  the  myopic,  and  the  hy- 
permetropic eye.]  The  retina,  or  inner  tunic  of  the  eye,  contains 
the  nervous  elements  by  whose  action  the  system  of  refracted  rays 


THE   LAYERS   OF   THE   RETINA. 


179 


is  changed  into  a  mosaic  of  nerve-commotions.  But  light  does  not 
act  as  a  stimulus  to  the  nei'vous  substance,  either  fibres  or  cells, 
unless  it  have  an  intensity  which  is  neai'ly  deadly  to  that  sub- 
stance. Since  we  are  able  to  see  the  feeblest  rays  of  the  moon  as 
reflected  from  white  paper,  the  nervous  excitation  which  is  the  con- 
dition of  vision  cannot  be  produced  by  the  direct  action  of  light  on 
the  nerve-fibres  or  nerve-cells  of  the  eye.  A  photo-chemical  sub- 
stance and  process,  as  well  as  a  special  end-apparatus,  seems  there- 
fore to  be  necessarily  involved  in  the  problem  which  is  given  to 
the  retina  to  solve. 

§  19.  The  nervous  and  other  elements  of  the  retina  are  arranged 

Outer  surface. 
10  ^^^^m^WS^msmm!mPm«^fr?^y^'^'    10 Layer  of  pigment  cells. 


9 Layer  of  rods  and  cones. 


S Membrana  limitans  externa. 


7  Outer  nuclear  layer. 


f    ....  Outer  molecular  layer. 


y  Inner  nuclear  layer. 


[5reJ'?|tdg*|!'„'K|      4  . . .  .Inner  molecular  layer. 


.  Layer  of  nerve-cells. 


. . .  Layer  of  nerve-fibres. 


=^^-:^:|^^^:  J . . .  .Membrana  limitans  interna. 
Inner  surface. 
Fig.  54. — Diagrammatic  Section  of  the  Human  Retina.     (Schultze.) 

in  tlie  following  ten  layers,  counting  from  within  outward  and 
backward  :  (1)  the  membrana  limitana  interna,  which  is  the  retinal 


180 


f-  .i„<;  A/     '    '   ■    ' — 


Fig.  55.— Diagrammatic  represen- 
tation of  the  Connections  of  the 
Nerv('  -  fibres  in  the  Retina. 
(Schultze.)  Tlie  numbers  have 
the  same  reference  aa  in  Fig.  54. 


THE   HUMAN   EYE. 

border  toward  the  vitreous  body  ;  (2)  the 
layer  of  optic  nerve-fibres  distributed  from 
the  papilla  where  this  nerve  breaks  in 
through  the  tunics  of  the  eye  ;  (3)  the 
ganglion-cell  layer  ;  (4)  the  imier  molecular 
layer  ;  (5)  the  inner  nuclear  layer  ;  (6)  the 
outer  molecular  layer  ;  (7)  the  outer  nu- 
clear layer ;  (8)  the  membrana  limitans 
externa ;  (9)  the  bacillary  laj'er,  or  layer 
of  rods  and  cones  ;  (10)  the  pigmenl-epiihe- 
lium  layer.  The  membranes  (Nos.  (1) 
and  (8))  are  not  really  uninterrupted 
layers,  but  an  extremely  fine  network. 

By  no  means  all  the  retinal  substance 
is  nervous.  Indeed,  the  numerous  radial 
fibres  {fibres  of  Midler)  which  seem  to 
penetrate  its  entire  thickness  are  now  held 
to  be  in  great  part  elements  of  the  suj)- 
porting  tissue  ;  moreover,  the  whole  con- 
nective substance  is  a  kind  of  sponge-like 
tissue,  in  the  gaps  of  which  the  true  ner- 
vous elements  lie  embedded.  The  gaps 
thus  filled  are  especially  large  in  the 
second,  third,  fifth,  and  seventh  layers. 

A  description  of  the  undoubtedly  ner- 
vous elements  of  the  retina  includes  the 
following  particulars  :  (a)  The  retinal 
fibres  of  the  optic  nerve  lie  parallel  to  the 
surface,  are  non-medullated,  and  extreme- 
ly fine  ;  in  general,  they  are  arranged  in 
ray-like  bundles,  radiating  on  all  sides 
from  the  place  of  the  entrance  of  the 
nerve.  The  arrangement  is  special  at  the 
yellow  spot,  so  as  to  surround,  and  not 
cover  it.  This  nerve-fibre  layer  is  thickest 
at  the  papilla  of  the  retina,  and  diminishes 
continuously  from  this  sjjot  toward  the 
ora  serrata ;  at  about  one-third  of  the 
distance  it  becomes  single.  (6)  The  gan- 
glion-cells, which  form  the  principal  part 
of  layer  No.  3,  like  the  multipolar  cells  of 
the  rest  of  the  cerebro-spinal  sj-stem, 
have  one   large   process   of   more  trans- 


THE   LATER   OF   RODS   AISTD   CONES. 


181 


lucent  appearance.  This  process  subdivides  into  fibrils  of  vanishing 
fineness,  that  enter  and  are  lost  in  the  next  layer.  At  the  yellow 
spot  these  cells  are  eight  or  ten  deep  ;  from  this  centre  they  dimin- 
ish toward  the  ora  serrata,  where  spaces  are  found  between  the 
cells,  (c)  The  nervous  elements  of  the  inner  molecular  layer  (No.  4) 
are  not  clearly  made  out.  They  probably  consist  of  extremely  fine 
filaments,  which  are  connected  with  the  external  processes  of  the 
ganglion-cells,  (d)  Most  of  the  nucleus-like  bodies  of  the  inner 
nuclear  layer  (No.  5)  are  probably  nervous.  Each  such  body  has 
two  processes — one  directed  inward,  the  other  outward.  The 
former  is  thought  to  be  connected  with  the  filaments  of  the 
inner  (No.  4),  and  the  latter  with  those  of  the  outer  (No.  6)  molec- 
ular layer.  («)  In  the  outer  molec- 
ular layer  (No.  6)  are  nervous  fila- 
ments, like  those  in  No.  4,  which  are 
probably  connected  with  the  external 
processes  of  the  inner  nuclear  layer. 
Here  are  also  found  numerous  star- 
shaped  cells  probably  not  nervous. 
(/)  In  the  outer  nuclear  layer  (No. 
7)  the  undoubtedly  nervous  elements 
preponderate.  Each  nucleus-like 
body  in  this  layer  is  connected  by  a 
radial  fibre  with  one  of  the  nervous 
elements  of  the  rod- and- cone  layer 
(No.  9).  These  nuclear  bodies  are 
called  rod-granules  and  cone-granules 
respectively,  and  are  to  be  distin- 
guished, not  only  by  their  connection 
with  these  elements,  but  also  by 
their  size  and  position  ;  the  latter  are 
larger,  and  lie  on  the  more  external 
side  of  the  layer,     {g)  The  layer  of 

rods  and  cones  (No.  9)  consists  of  a  multitude  of  elongated  bodies 
arranged  side  by  side,  like  rows  of  palisades,  with  their  largest  ex- 
tension in  the  radial  direction.  These  bodies  are  of  two  kinds — 
one  cylindrical,  and  called  "rods  of  the  retina,"  the  other  rather 
flask-shaped,  and  called  "cones  of  the  retina." 

The  rods  extend  the  entire  thickness  of  the  layer,  and  are  about 
3^„  inch  in  length,  but  the  cones  are  shorter  ;  the  rods  are 
about  TXoTTo  ^^^^^  ^^  diameter,  the  smallest  cones  of  the  central 
depression  ^  o|)qq  inch.  The  inner  ends  of  both  are  continuous 
with  the  rod-fibres   and  cone-fibres  of   the  outer  nuclear  layer. 


Fig.  56. — Diagrammatic  Section  of  tne 
Posterior  Part  of  the  Retina  of  a  Pig. 
80»/i.  (Schultze.)  7,  part  of  outer  nu- 
clear laj"er ;  8,  membrana  limitana  ex- 
terna ;  9,  rods  n.nd  cones.  Each  of  the 
cones,  which  are  in  very  close  apposition, 
contains  in  its  inner  segment  a  highly  re- 
tractile bod3',  the  func  ion  of  which  is 
unknown. 


182 


THE  HUMAN   EYE. 


Each  rod  or  cone  is  composed  of  an  inner  and  outer  segment 
or  limb ;  the  latter  is  highly  retractile,  the  former  only  feebly  so. 
The  inner  limbs  appear  under  the  microscope  like  a  mass  of  pro- 
toplasm. The  appearance  of  a  most  delicate  longitudinal  line  in 
the  inner  and  outer  segments  has  led  to  the  belief  that  a  nerve- 
fibril  is,  as  it  were,  drawn  through  their  axis.     The  description 


Fig.  57. — Rods  and  Cones  of  the  Human  Retina.  (Schultze.) 
A,  showing  inner  segments  of  the  rods,  .s'  s  s,  and  of  the 
cones,  zz';  the  latter  in  connection  with  the  cone-nuclei  and 
fibres  as  far  as  the  outer  molecular  layer.  """Z].  A  inner 
segment  of  a  cone  with  a  cone-nucleus.  ^200^^,  C,  isolated 
interior  portion  of  a  cone. 


Fig.  58. — Rod  and  Cone  from 
the  Human  Retina,  preserved 
in  perosmic  acid,  showing 
the  fine  fibres  of  the  surface 
and  the  different  lengths  of 
the  internal  segment,  '"""/i. 
(Schultze.)  The  outer  seg- 
ment of  the  cone  is  broken 
into  disks  which  are  still  ad- 
herent. 


of  the  two  shows  that  there  is  no  essential  anatomical  difference 
between  the  rods  and  cones  ;  nor  are  we  able  to  distinguish  any 
difference  in  their  physiological  significance.  The  distribution  of 
the  two  elements  is  different  for  different  parts  of  the  retina.  In 
the  yellow  spot  only  cones  appear,  but  these  are  of  more  slender 
form,  and  of  increased  length,  so  that  not  less  than  one  million  are 
supposed  to  be  set  in  a  square  y^  inch  ;  '  while  not  far  from  this 
'  See  Le  Conte,  Sight,  p.  58.     New  York,  1881. 


YELLOW   SPOT  AND   BLIISTD   SPOT. 


183 


m^ 


Figs.  59  and  60.— Superficial  Aspectof  the  Arrangement 
of  the  Rods  and  Cones  in  the  Retina.  *"%.  (Schultze.) 
The  former  is  from  the  region  of  the  macula  lutea  ; 
the  latter  from  the  peripheral  region. 


spot  each  cone  is  surrounded  by  a  crown-shaped  border  of  rods. 
Toward  the  ora  serrata  the  cones  become  continually  rarer.     In 
close   connection   with   the 
rods   and   cones   stand  the 
cells  of  the  pigment-epithe- 
lium.    These   cells   form  a 
regular  mosaic  of  flat,  six- 
sided  cells,  which  send  out 
pigmented     processes 
tween  the  outer  limbs  of  the 
rods  and  cones. 

The  fibres  of  the  optic 
nerve  are  supjDOsed  to  be 
connected  with  the  rods  and  cones  by  means  of  the  ganglion -cells, 
and  of  the  radial  fibres  in  which  the  granules  of  the  outer  and  inner 
nuclear  layers  are  embedded. 

§  20.  Two  minute  portions  of  the  inner  surface  of  the  retina  re- 
quire to  be  distinguished  from  the  rest  of  its  area  ;  the  yellow  spot 
(macula  lutea)  and  the  "  blind  spot "  [papilla  optica).  The  yellow  spot 
S  Ch  is  of  oval  shape,  about  -^-^  of  an 
inch  in  its  long  diameter,  and  has 
in  the  centre  a  depression  called 
ihQ  fovea  centralin.  It  is  the  place 
of  clearest  vision,  and  the  physi- 
ological centre  of  the  eye.  About 
\  of  an  inch  inside  the  eye  from 
the  middle  of  the  yellow  spot  is 
the  middle  of  the  papilla,  or  place 
where  the  optic  nerve  breaks  into 
the  retina.  The  blind  spiot,  or 
portion  of  the  retina  which  can 
be  experimentally  shown  to  be 
inoperative  in  vision,  has  been 
proved  by  Helmholtz  to  corre- 
sj)ond  in  both  size  and  shape  to 
that  covered  by  this  papilla.  Its  diameter  is  about  J^  or  J-j  of  an 
inch,  varying  considerably  for  different  eyes.  It  is  wanting  in  all 
the  nervous  elements. 

§  21.  In  answer  to  the  question,  What  elements  of  the  retina  are 
directly  affected  by  the  light  ?  both  anatomy  and  physiology  refer 
to  the  layer  of  rods  and  cones.  This  layer  alone  possesses  that 
mosaic  nervous  structure  which  appears  to  correspond  to  the  de- 
mands made  upon  the  end-apparatus  of  vision.     It  can  be  demon.- 


PlG.  61.— Equatorial  Section  of  the  Right  Eye, 
showing  the  Papilla  of  the  optic  nerve,  the 
Blood-vessels  radiating  from  it,  and  the 
Macula  lutea.  7i-  (Henle.)  S,  sclerotic; 
Ch,  choroid  ;  and  R,  retina. 


184  THE   HUMAN   EYE. 

strated  that  the  waves  of  light  pass  through  the  structure  of  the 
retina,  and  that  the  nervous  process  must  begin  in  the  back  part  of 
this  structure.  Indeed,  it  is  possible,  by  an  experiment  (devised  by 
Purkinje),  to  perceive  with  one's  own  retina  the  aborescent  figure 
formed  by  the  shadow  of  the  blood-vessels  expanded  upon  its  front 
part. 

§  22.  We  have  already  seen  (Chapter  I.,  §§  14,  15)  that  a  chemi- 
cal process  may  reasonably  be  conjectured  to  accompany  the  action 
of  the  nerves  in  general.  Undoubtedly  a  photo-chemical  process 
is  concerned  in  vision.  But  after  all  the  careful  researches  of  many 
observers,  especially  of  Ktihne  '  and  his  pupils — it  is  difficult  to 
point  to  any  results  of  chemical  investigation  which  serve  better  to 
define  the  exact  nature  of  the  physiological  action  of  the  end-oi'- 
gaus  of  the  eye.  The  relation  of  the  light  to  any  chemical  pro- 
cesses which  may  take  place  in  the  gray  substance  of  the  retina  can 
be  only  indirect.  The  opto-chemical  hypothesis  must,  therefore, 
regard  the  epithelial  cells,  with  which  the  end-fibrils  of  the  optic 
nerve  are  in  physiological  connection,  as  the  bearers  (Trager)  of  cer- 
tain photo-chemically  decomposable  materials  or  visual  substances 
(Seh^toff^e)  ;  these  substances,  however,  cannot  excite  chemically 
the  irritable  part  of  the  visual  cells — the  protoplasm  of  the  inner 
limbs  of  the  rods  and  cones — without  being  themselves  decomposed. 
Visual  substance  is  necessarily  some  kind  of  matter  easily  decom- 
posable by  light,  or  chemically  sensitive  to  light.  The  first  process, 
then,  in  the  excitation  of  the  optic  nerve,  is  the  decomposition  by 
the  light  of  some  substance  found  in  certain  epithelial  elements  of 
the  retina.  The  second  process  is  the  action,  as  visual  excitants 
(Sehreger),  of  the  decomposition-products  of  the  epithelial  cells 
upon  the  protoplasm  of  the  end-organs.  But  in  order  that  such 
decomposition-products  may  act  as  excitants  of  the  end-organs  of 
vision,  the  visual  substance  must  be  rightly  placed — that  is,  it  must 
be  in  local  connection  with  the  protoplasm  of  the  outer  limbs  of 
the  rods  and  cones.  The  relation  of  the  two  last  layers  of  the 
retina  is  such  as  to  secure  this  necessary  connection.  We  are  as 
yet  unable,  however,  to  say  what  are  the  visual  substances  which 
the  successful  working  of  the  opto-chemical  hypothesis  demands. 
The  location  of  the  pigmentum  nigrum,  and  the  changes  produced 
m  it  by  light,  favor  the  conjecture  that  this  substance  is  of  the 
most  fundamental  and  general  importance  for  visual  sensations. 
Visual  purple  may  also  be  supposed  to  be  a  visual  substance.  The 
fact  that  light  of  different  wave-lengths  effects  changes  in  this  pig- 

'  The  few  statements  here  given  are  taken  for  the  most  part  from  the  article 
of  this  investigator  in  Hermann's  Handb.  d.  Physiol.,  III.,  i. ,  pp.  335  fE. 


PIGMENTS   OF   THE   EYE.  185 

ment  with  different  degrees  of  speed,  suggests  the  view  that  it  is 
related  to  the  susceptibility  of  the  eye  for  different  colors.  But 
since  invertebrates  do  not  have  the  visual  purple  ;  since  the  cones 
(a  thing  which  no  one  doubts)  see  without  this  purple,  and  since 
the  rods  of  some  animals,  such  as  hens  and  doves,  and  the  rods  of 
the  ora  serrata,  perform  their  functions  without  it,  this  pigment 
can  scarcely  be  said  to  be  the  only  visual  substance.  The  opto-chem- 
ical  hypothesis,  then,  seems  to  require  several  colored  visual  sub- 
stances. Moreover,  since  animals  can  see  with  bleached  retinas, 
and  albinos  have  the  power  of  vision,  we  are  compelled  to  assume 
also  a  colorless  visual  pigment.  As  to  the  nature  of  the  chemical 
changes  necessary  to  be  produced  in  the  protoplasm  of  the  outer 
limbs  of  the  rods  and  cones  by  the  action  of  the  decomposition- 
products  of  the  visual  substances,  we  are  quite  ignorant. 

§  23.  The  end-organ  of  hearing  is  the  Ear.  But  in  this  case,  as 
in  that  of  the  eye,  a  very  large  part  of  the  apparatus  of  sense  is  sig- 
nificant simjDly  as  a  contrivance  for  applying  the  stimulus  to  the 
true  end-organ,  to  the  differentiations  of  epithelial  cells  and  nervous 
cells  connected  with  the  terminal  fibrils  of  the  sensory  nerve.  The 
entire  human  ear  consists  of  three  parts,  or  ears  ;  namel}^  the  ex- 
ternal ear,  the  middle  ear,  or  tympanum,  and  the  inner  ear,  which 
is  also  called  the  "  labyrinth,"  from  its  complex  construction. 

I.  The  External  Ear — exclusive  of  the  cartilaginous  plate  which  is 
extended  from  the  side  of  the  head — consists  of  (a)  the  concha,  a 
deep  hollow,  and  {b)  the  external  meatus,  or  passage  leading  from  the 
bottom  of  this  hollow  to  the  drum  of  the  ear.  The  concha  is  prob- 
ably of  little  or  no  use  in  sharpening  our  perceptions  of  sound  ; 
for  if  a  tube  be  inserted  so  as  to  secure  a  canal  for  the  air  to  the 
drum  of  the  ear,  the  entire  concha  may  be  filled  with  wax,  and  the 
result  is  to  increase  rather  than  diminish  the  sharpness  of  the 
sound.  It  is  possible,  however,  that  vibrations  of  more  than  one 
thousand  in  a  second  are  concentrated  by  reflection  '  from  the  con- 
cha. The  external  ear  appears  to  be  of  some  service  in  perceiv- 
ing the  direction  of  sound.  Kinne's  experiments  seem  to  show 
that — as  Harless  '  thought— the  cartilage  of  the  ear  can  be  thrown 
into  sympathetic  vibration  with  certain  acoustic  waves,  and  so  re- 
inforce the  sound.  At  best,  however  such  work  done  by  the  con- 
cha is  small. 

The  most  patent  office  of  the  external  meatus  is  the  protection 
of  the  ear-drum  ;  the  passage  is  so  curved  that  the  drum  cannot  be 

'  See  Hensen,  Physiologie  d.  Gehors,  in  Hermann's  Haadb.  d.  Physiol., 
III.,  ii.,  p.  23. 

-Article  Horen,  in  Wagner's  Handworterbuch  d.  Physiol.,  FV  ,  1853. 


186 


THE  HUMAN   EAE. 


reached  from  the  outside  in  a  straight  hne.  Helmholtz  called  at- 
tention to  the  fact  that  certain  tones  of  a  high  pitch  resound 
strongly  in  the  ear  when  the  meatus  is  of  normal  length,  but  cease 
so  to  resound  when  its  length  is  increased  artificially.  The  meatus 
probably,  therefore,  modifies  certain  tones  by  its  own  resonant 
action — strengthening  the  high  ones,  and  deadening  the  low,  in 
some  degree. 

Various  simple  experiments — such  as  placing  a  resounding  body 
in  contact  with  the  teeth — prove  that  the  surrounding  cranial  bones 
conduct  sound  to  the  ear.  It  is  probable,  howevei",  that  the  path 
of  such  conduction  is  not,  for  the  most  part,  as  was  formerly  sup- 
posed, directly  to  the  inner  ear  by  way  of  the  cranial  and  petrous 
bones,  but  indirectly,  through  the  ear-drum  and  bones  of  the  middle 
ear  to  the  fenestra  ovalis.  The  amount  of  direct  conduction  pos- 
sible, has  not  as  yet  been  determined  precisely. 

§  24.  n.  The  Middle  Ear,  or  Tympanum,  is  a  chamber  irregu- 
larly cuboidal  in  form,  and  situated  in  the  temporal  bone,  between' 
the  bottom  of  the  meatus  and  the  inner  ear.     Its  outer  wall  is  (a) 


Fio.  62.— Dnim  of  the  Right  Ear  with  the  Ham- 
mer, seen  from  the  inside.  2/,.  (Henle.)  1, 
chorda  tympani ;  2,  Eustachian  tube  ;  *,  ten- 
don of  the  tensor  tympani  muscle  cut  off  close 
to  its  insertion  ;  m  a,  anterior  ligament  of  the 
malleus ;  M  c  p,  its  head  ;  and  M  1,  its  long 
process.     S  t  p,  Spina  tympanica  posterior. 


Cliorda  tijDiEani 


Fig.  63.— Side  Wall  of  the  Cavity  of  the  Tym- 
panum, with  the  Hammer  (M)  and  the  Anvil 
(.J).  The  former  shows  the  connection  of  its 
handle  with  the  drum.  T,  Eustachian  tube. 
^/,.     (Gegenbaur.) 


the  membrana  tympani,  which  consists  of  three  layers — an  external 
tegumentary,  an  internal  mucous,  and  the  intermediate  membrana 
propria,  composed  of  unyielding  fibres  arranged  both  radially  and 
circularly.  In  the  inner  wall,  which  separates  the  tympanum  from 
the  labyrinth,  are  two  openings  or  windows — the  fenestra  ovalis, 
which  corresponds  to  the  vestibule  of  the  labyrinth,  and  the  fenestra 
rotunda,  which  corresponds  to  the  tympanic  passage  in  the  cochlea. 
Near  its  anterior  part  the  tympanum  opens  into  (6)  the  Eustachian 


THE   THREE   AUDITORY   BONES.  187 

tube,  a  canal  which  communicates  with  the  nasal  compartment  of 
the  pharynx. 

(c)  The  auditory  bones  are  three  in  number,  called  Malleus, 
Incus,  and  Stapes,  and  arranged  so  as  to  form  an  irregular  chain 
stretched  across  the  cavity  from  the  outer  to  the  inner  wall  of  the 
tympanum.  The  malleus  has  a  head,  separated  by  a  constricted 
necli  from  an  elongated  handle  ;  its  handle  is  connected  with  the 
centre  of  the  membrana  tympani  ;  its  head  articulates  with  the  in- 
cus. The  incus  has  a  body  and  two  processes.  On  the  front  sur- 
face of  the  body  is  a  saddle-shaped  hollow,  in  which  the  head  of 
the  malleus  fits  ;  the  short  process  is  bound  by  a  ligament  to  the 
posterior  wall  of  the  tympanum  ;  the 
long  process  ends  in  a  rounded  pro- 
jection {os  orbicular e)  through  which 
it  articulates  with  the  stapes.  The 
stapes,  or  stirrup-shaped  bone,  has  "    "' 

a  head  and  neck,  a  base  and  two 
crura.  The  head  articulates  with 
the  incus  ;  from  the  constricted  neck 
the  two  crura  curve  inward  to  the 
base,  which  is  attached  to  the  fenes- 
tra ovalis.  These  bones  are  moved 
on  each  other  at  their  joints  by  {d) 
two  or  three  small  muscles — the  ten-  „     ^,     „        ^.^  „  .     ^. 

Fig.  64.  — Bones  of  the  Ear,  as  seen  in  their 
SOr  tympani,  the  stapedius,  and,  more        connection  from  in  front.     Vi-     (Henle.) 

I,  Incus  (anvil _),  of  which  lb  is  the  short, 
doubtfully,  the  taxator  tympani.  Ihe  and  Ilthe  Icng,  i>rocess;  c.  its  body,  and 
n      1         e     L^  •        •  j.     i     •     j.       xi  P'>  ^^^  process  for  articulation  with  the 

first     01     these    is    inserted    into    the       st&^'esiprocessusorbiciaaris.)   M,  Malleus 
TT  J.1  J.  T  L  (hammer),  of  which  Mc  is  the  neck,  Mcp 

malleus,  near  the  root,  and  serves  to        the  head,  mi  the  long  process,  and  Mm  the 

tighten  the  tympanic  membrane  by  erpUuhm^cp.^'  '"'^''  ^''^™''^'  ''"^  '*' 
drawing  the  handle  of  the  malleus 

inward  ;  the  stapedius  is  inserted  into  the  neck  of  the  stapes, 
but  its  function  is  doubtful — apparently  it  draws  the  stapes  from 
the  fenestra  ovalis,  and  so  diminishes  the  pressure  of  the  chain 
of  bones  in  that  direction.  The  laxator  tympani  is  inserted  into 
the  neck  of  the  same  bone,  and  its  action  has  been  supposed  by 
some  to  be  antagonistic  to  that  of  the  tensor  tympani ;  but  its 
muscular  character  is  now  denied  by  most  observers. 

§  25.  The  general  of&ce  of  the  tympanum  may  be  described  as 
that  of  transmitting  the  acoustic  waves  to  the  inner  ear,  while  at  the 
same  time  modifying  their  character.  Some  modification  is  neces- 
sary in  order  that  these  waves  may  occasion  such  \T.brations  in  the 
elements  of  the  inner  ear  as  shall  be  adapted  for  the  excitation  of 
its  end-organs.     The  acoustic  motion  of  the  molecules  of  air,  in  the 


188  THE   HUMAN   EAR. 

form  in  wliicli  it  reaches  the  ear-drum,  has  a  large  amphtude,  but 
a  small  degree  of  intensity.  This  motion  must  be  changed  into  one 
of  smaller  amplitude  and  greater  intensity  ;  and  it  must  be  trans- 
mitted, with  as  little  loss  as  possible,  to  the  fluids  of  the  labyrinth. 
The  transmitting  vibrating  media  must  also  have  the  power  of  an- 
swering to  the  different  tones  of  any  pitch  perceptible  by  the  ear. 
The  description  of  the  manner  in  which  this  apparatus  of  membrane 
and  bones  solves  so  complicated  a  mechanical  problem  belongs  to 
the  physics  of  anatomy  ;  it  has  been  worked  out  with  great  detail 
by  Helmholtz  and  others,  although  certain  points  still  remain  un- 
solved.    "VVe  can  here  only  indicate  one  or  two  particulars. 

A  flat  membrane,  evenly  stretched,  whose  mass  is  small  in  pro- 
portion to  the  size  of  its  superficies,  is  easily  thrown  into  vibration 
by  the  impact  of  acoustic  waves  upon  one  of  its  sides.  Such  a 
membrane  resjjonds  readily  to  tones  which  approach  its  own  funda- 
mental tone  ;  but  if  divergent  tones  are  sounded  the  membrane  is 
unaffected.  A  motion  which  consists  of  a  series  of  harmonious 
partial  tones  cannot  then  be  repeated  by  such  a  membrane  in  the 
form  in  which  the  air  brings  it.  If,  then,  the  membrane  of  the 
tympanum  were  not  so  arranged  and  connected  as  to  have  no  pre- 
pondei'ating  tone  of  its  own,  it  could  not  be  the  medium  of  our 
hearing  a  great  variety  of  tones.  The  projaerty  of  taking  up  with 
the  vibrations,  as  it  were,  of  a  large  scale  of  tones  is  secured  for  the 
tympanum  by  its  funnel-shaped  form  and  by  its  being  loaded.  It 
is  contracted  inward  into  a  dej)ression  of  the  right  shape  by  means 
of  the  handle  of  the  hammer  ;  it  is  therefore  unequally  and  only 
slightly  stretched,  and  has  no  fundamental  tone.  It  is  also  load- 
ed with  the  auditory  bones,  Avhich  deprive  it  of  every  trace  of  such 
a  tone  and  act  as  dampers  to  prevent  long-continued  vibrating. 
Moreover,  since  the  apex  of  its  funnel  bulges  inward,  the  force  of 
the  vibrations  from  all  sides  is  concentrated  in  vibrations  of  greater 
intensity  in  the  centre,  where  it  is  spent  in  setting  the  chain  of  ear- 
bones  in  motion. 

The  acoustic  vibrations  of  the  auditory  bones,  which  are  occa- 
sioned by  the  movements  of  the  ear-drum,  are  not  longitudinal, 
but  transverse  ;  they  do  not,  however,  resemble  the  vibrations  of  a 
stretched  cord  or  a  fixed  pin.  They  do  not  vibrate  by  reason  of 
their  elasticity,  but  like  very  light  small  levers — vibrating  as  a  sys- 
tem, with  a  simultaneous  motion  around  a  common  axis.  Direct 
observation  of  these  bones  in  motion  shows  that  their  sympathetic 
vibrations  vary  greatly  for  tones  of  different  pitch  and  similar  in- 
tensity, from  a  scarcely  observable  motion  to  a  surprisingly  great 
elonpfation. 


THE  EUSTACHIAN   TUBE. 


189 


The  effect  of  the  muscles  of  the  tympanum  upon  the  transmis- 
sion of  tones  of  different  pitch  is  not  as  yet  clearly  demonstrated. 
In  general,  the  stretching  of  the  tensor  muscle,  within  the  hmits 
which  have  thus  far  been  investigated,  seems  to  weaken  the  higher 
much  less  than  the  lower  tones.  But  the  tension  of  the  drum  un- 
der the  influence  of  this  muscle  does  not  indicate  the  slightest 
change  on  passing  from  low  to  high  tones.  The  stretching  of  the 
tendon  of  the  stapedius  muscle  has  no  observable  influence  on  the 
acoustic  vibrations  of  the  tympanum. 

§  26.  The  Eustachian  Tube,  when  in  its  normal  position,  is  neither 
closely  shut  nor  wide  open.  Its  office  is  to  effect  a  renewal  of  the 
air  in  the  tympanum,  to  maintain  the  equilibrium  of  atmospheric 
pressure  on  both  sides  of  the  tympanic  membrane,  and  to  convey 
away  the  fluids  which  collect  in  the  tympanic  cavity.  If  it  re- 
mained open,  so  as  to  permit  the  acoustic  waves  of  the  air  fi'om  the 
mouth  to  enter,  our  own  voices  would  be  heard  as  a  roaring  sound, 
and  the  passage  of  air  inward  and  outward  during  respiration 
would  affect  the  position  and  tension  of  the  tympanic  membrane. 
That  it  is  opened,  however,  on  swallowing,  Valsalva  proved  two 
centuries  ago.  For  if  we  keep  the  nose  and  mouth  closed  and  then 
swallow,  with  the  cheeks  blown  violently  out,  a  feeling  of  press- 
ure is  felt  in  the  ears  and  the  hearing  is  weakened.  These  effects 
are  due  to  the  forcing  of  the  air  through  the  Eustachian  tube  into 
the  tympanic  cavity.  The  tube  is  thus  of  indirect  service  in  re- 
spect to  the  physiological  functions  of  the  middle  ear. 

§  27.  III.  The  Internal  Ear,  or  Labyrinth,  is  the  complex  organ 
in  which  the  terminal  fibrils  of  the  auditory  nerve  are  distributed 
and  the  end-organs  of  hearing  situated.  It  lies  in  a  series  of  cav- 
ities channelled  out  of  the  petrous  bone.  It  consists  of  three  parts 
—the  Vestibule,  the  Semicircular  Canals,  and  the  Cochlea.  In  each 
osseous  part  a  membranous  part  is  suspended,  corresponding  to  it 
in  shape,  but  filHng  only  a  small  portion  of  the  bony  cavity  which 
contains  it.  It  is  in  the  labyrinth  that  the  acoustic  waves  trans- 
mitted by  the  tympanum  are  analysed  and  changed  from  a  physi- 
cal molecular  process  to  a  nerve-commotion,  by  the  special  end- 
apparatus  of  hearing. 

(A)  The  Vestibule  is  the  central  cavity  of  the  internal  ear  ;  it  is 
the  part  of  the  labyrinth  which  appears  first  in  animals  and  is  most 
constant.  The  membranous  vestibule  is  composed  of  two  sac-like 
dilatations-the  upper  and  larger  of  which  is  named  utriculus,  the 
lower  mcculas.  In  its  outer  wall  is  the  fenestra  ovalis  ;  its  anterior 
wall  communicates  with  the  scala  vestibuli  of  the  cochlea,  and  at  its 
posterior  wall  the  fine  orifices  of  (B)  the  Semicircular  Canals  open 


190 


THE  HUMAN   EAE. 


into  the  utriculus.  These  canals  are  three  in  number,  are  bent  so 
as  to  form  nearly  two-thirds  of  a  circle,  and  are  about, an  inch  in 
length  and  ^^  of  an  inch  in  diameter.     They  are  called  the  supe- 


No.  1. 


No.  3. 


No.  3. 


Ke  vaa 
Ks    \     \  ^^ 


■?pa 


Fig.  65.  No.  1,  Osseous  Labyrinth  of  the  Left  Ear,  from  below  ;  No.  2,  of  the  Right  Ear,  from 
the  inside  ;  No.  3,  of  the  Left  Ear,  from  above.  (Henle.)  Av,  aqueduct  of  vestibule  ;  Fc.  fossa 
of  the  cuchlea  ;  Fee,  its  fenestra  {rotunda)  ;  Pv,  fenestra  of  the  vestibule  {ovalU)  ;  ha,  external 
ampulla  ;  h,  external  semicircular  canal ;  Tsf,  traetua  spirnH-i  foraminosus  ;  vaa,  ampulla  of 
the  superior  semicircular  canal ;  vc,  posterior  semicircular  canal ;  and  vpa,  its  ampuUa. 

rior,  the  posterior  or  vertical,  and  the  external  or  horizontal  canals. 
The  contiguous  ends  of  the  superior  and  posterior  canals  blend  to- 
gether and  have  a  common  orifice  into  the  vestibule.     They  all 


Fee 


Fio.  66.— Osseous  Cochlea  of  the  Right  Ear,  ex- 
posed from  in  front.  ■•/, .  (Henle.)  t,  section 
of  the  division-wall  of  the  cochlea  ;  +t,  upper 
end  of  the  same.  Fee,  Fenestra  ;  H,  hamulus ; 
Md,  modiolus ;  Ls,  lamina  spiralis. 


Fig.  67. — Cross-section  through  the  Acoustic 
Nerve  and  the  Cochlea,  ^/j.  (Henle.)  Nc, 
nerve  of  the  cochlea  ;  Nv,  nerve  of  the  vesti- 
bule ;  St,  .scala  tympani ;  Sv,  scala  vestibuli  ; 
and  between  them  the  ductus  cochlearis,  Dc. 
Ls  and  Md,  as  in  preceding  figure. 


have  a  regular  relative  position,  their  planes  being  at  right  angles 
to  each  other.  Near  the  vestibule  they  dilate  to  about  twice  their 
average  diameter  and  form  the  so-called  ampullce.    Both  the  osseous 


STEUCTUKE  OF  THE  COCHLEA. 


191 


Ligamentuiii 
spirals 


vestibule  and  the  osseous  canals  contain  a  fluid  (the  penlymi^h),  in 
which  the  membranous  vestibule  and  canals  are  suspended  ;  the 
membranous  labyrinth  is  also  distended  with  a  similar  fluid  (the 
endolymph). 

(C)  The  Cochlea  is  by  far  the  most  complex  part  of  the  laby- 
rinth ;  it  is  about  ^  of  an  inch  long,  and  is  shaped  like  the  shell  of 
a  common  snail.  It,  too,  consists  of  a  membranous  sac  embedded  in 
the  osseous  cavity.  The  whole  passage  of  the  cochlea  is  imperfectly 
divided  into  two  canals  by  a  partition-wall  of  bone,  which  is  wound 
2|-  times  around  an  axis  (the  modiolus),  from  the  base  to  the  apex, 
somewhat  like  a  spiral  stair-case.  It  is  called  the  osseous  lamina 
spiralis.  Of  the  two  canals  or  passages  thus  formed,  the  one  which 
faces  the  base  of  the  cochlea  is  called  the  scala  tympani  ;  since  it 
has  its  origin  in  the  cir- 
cular aperture  (fenestra 
rotunda)  which  leads  to 
the  tympanic  cavity.  The 
other,  which  faces  to- 
ward the  apex,  opens 
into  the  vestibule,  and 
is  called  the  scala  vesti- 
buli.  At  the  apex  of  the 
cochlea  these  two  scalae 
communicate  with  each 
other  through  a  small 
hole  [helicotrema).  The 
division  of  the  mem- 
branous cochlea  is  com- 
pleted by  a  membrane 
(the  basilar  membrane,  or  membranous  spiral  lamina),  which  bridges 
the  interval  between  the  free  edge  of  the  osseous  spiral  lamina  and 
the  outer  wall  of  the  passage  ;  it  is  attached  to  this  wall  by  the  spiral 
ligament.  Another  membrane  (the  membrane  of  Reissner)  arises 
from  a  spiral  crest  (limbus,  or  crista  spiralis)  attached  to  the  free 
edge  of  the  osseous  lamina,  and  extends  to  the  spiral  ligament,  so 
as  to  form  a  small  aqueduct  between  it  and  the  basilar  membrane 
(the  scala  intermedia,  or  ductus  cochlearis,  or  canal  of  the  cochlea). 
It  is  in  the  vestibule,  in  the  ampullae  of  the  canals,  and  in  the  scala 
intermedia  that  the  nervous  end-organs  of  hearing  are  to  be  found. 

§  28.  The  auditory  nerve,  on  approaching  the  labyrinth,  divides 
into  a  vestibular  and  a  cochlear  division.  The  former  enters  the 
vestibule  and  subdivides  into  five  branches — one  for  the  utriculus, 
one  for  the  sacculus,  and  one  for  each  of  the  three  ampullae.     In 


Fig. 

^7i 


3. — Section  through  one  of  the  Coils  of  the  Cochlea. 
(Schematic,  from  Gegenbaur.) 


192 


THE   HUMAIST   EAE. 


each  of  these  dilatations  the  membranous  wall  forms  a  projecting 
ridge,  called  the  crista  acoustica.  The  endothelial  investment  of 
the  crista  is  elongated  into  columnar  cells,  intercalated  between 
which  are  fusiform  cells.  Each  of  the  latter,  according  to  Max 
Schultze,  and  others,  has  the  peripheral  and  the  central  process 
with  which  we  are  already  familiar  in  the  nerve-cells  of  other  end- 
organs  of  sense.     The  peripheral  process  projects  into  the  eudo- 

lymph  as  an  auditory 
hair ;  while  the  central 
extends  into  the  subendo- 
thehal  tissue  where  the 
nerve-plexus  of  the  audi- 
tory nerve  ramifies,  with 
the  terminal  branches  of 
which  it  is  probably  con- 
tinuous. According  to 
more  recent  observers 
(Eetzius  and  others)  the 
auditory  hairs  are  con- 
nected with  the  columnar 
cells,  and  do  not  project 
into  the  endolymph,  but 
into  a  soft  material  of  in- 
distinctly fibrillar  struct- 
ure. The  inner  surface 
of  the  epithelium  of  the 
crista  is  thus  clothed  with 
a  thick-set  "  wood "  of 
these  hairs.  Max  Schultze 
found  their  length  to  be 
about  ^1^  inch — their  ul- 
timate ends,  however,  be- 
ing too  fine  to  discriminate.  Calcareous  particles,  called  "  ear- 
stones  "  (otoliths)  apj)ear  in  both  saccule  and  utricle,  embedded  in 
a  soft  matrix  and  lying  in  contact  with  the  nerve-epithelium.  In 
the  vestibule  the  hair-like  prolongations  of  the  epithelial  cells  are 
more  scanty  than  in  the  ampullae. 

§  29.  The  terminal  nerve-apparatus  of  the  cochlea  is  even  far 
more  complicated  and  remarkable.  The  cochlear  branch  of  the 
auditory  nerve  pierces  the  axis  of  the  cochlea  (modiolus)  and  gives 
off  lateral  branches  which  pass  into  the  canals  of  the  osseous  spiral 
membrane.  Here  they  radiate  to  the  membranous  spiral  lamina, 
and  are  connected  with  a  ganglion  of  nerve-cells  ;  beyond  the  gan- 


Fig.  69. — Scheme  of  the  Nerve-endings  in  the  Ampullse. 
(After  Kiidiiiger.)  1,  membranous  wall  of  the  anipiillag, 
with  a  structureless  border.  2  ;  through  which  the  nerve- 
fibre,  3,  sends  its  axis-cylinder,  4  ;  5,  plexiform  connection 
of  the  nerve-fibres  ;  6,  auditory  cells  ;  7,  supporting  cells ; 
8,  auditory  hairs. 


THE   OEGA]^   OF   CORTI. 


193 


glion  they  form  a  plexiform  expansion,  from  wliicli  the  delicate 
fibrils — losing  their  medullary  sheath  and  becoming  extremely 
fine  axis-cylinders — pass  through  a  gap  in  the  edge  of  the  lamina 
into  the  organ  of  Corti.  The  connection  of  their  ultimate  fibrils 
with  the  cone-cells  of  this  oi'gan  may  be  assumed,  but  is  difiicult  to 
demonstrate. 

The  organ  of  Corti  is  situated  on  that  surface  of  the  basilar 
membrane  which  is  directed  toward  the  ductus  cochlearis.  Its 
structure  is  a  wonderful  arrangement  of  cells.  Some  of  these  cells 
are  curved,  elongated,  and  placed  in  two  groups — an  inner  and  an 
outer.     They  are  called  the   "rods,"  or   "pillars,"  or   ''fibres  of 


Fig.  to. — Organ  of  Corti  in  the  Dog.  ^00/^.  (Waldeyer.)  h — c,  homogeneous  layer  of  the  basilar 
membrane ;  u,  its  vestibular  layer ;  v.  its  tympanal  layer  ;  d,  blood-vessel  ;  f,  nerves  in  spiral 
lamina ;  g,  epithelium  of  spiral  groove  ;  A,  nerve-fibres  passina;  toward  inner  hair-cells,  /,  k  ;  I, 
auditory  hairlets  on  inner  hair-cells ;  / — l^,  lamina  reticularis  ;  m,  heads  of  the  rods  of  Corti 
jointed  together  ;  the  inner  rod  seen  in  its  whole  length  ;  the  outer  one  broken  off :  n,  cell  at 
base  of  inner  rod  ;  p,  q.  r,  outer  hair-cells  ;  s.  a  cuticnlar  process  probably  belonging  to  a  cell 
of  Deitcrs  :  t,  lower  ends  of  hair-cells,  two  being  attached  by  cuticular  processes  to  the  basilar 
membrane  ;  to,  a  nerve-fibril  passing  into  an  outer  hair-cell ;  «,  a  sustenticular  cell  of  Deiters. 

Corti."  The  cells  of  the  inner  grouj)  rest  by  a  broad  foot  on  the 
inner  part  of  the  basilar  membrane,  project  obliquely  forward  and 
outward,  and  expand  into  a  dilated  head ;  the  cells  of  the  outer 
gi'oup  rest  in  the  same  way,  incline  forward  and  inward,  and  fit 
into  a  depression  in  the  head  of  the  cells  of  the  inner  group.  The 
two  thus  make  a  boio,  which  arches  over  an  exceedingly  minute 
canal  (the  canal  of  Corti)  formed  between  them  and  the  basilar 
membrane.  These  rods  of  Corti  increase  in  length  from  the  base 
to  the  apex  of  the  cochlea.  The  basilar  membrane  is  composed 
of  fibres  arranged  in  a  transverse  direction,  so  that  each  rod  rests 
upon  one,  or  upon  a  pair  of  these  fibres.  Internal  and  almost 
parallel  to  the  inner  group  of  rods  is  a  row  of  compressed  conical 
13 


194  THE  HUMAN   EAE. 

cells  with  short  and  stiff  hair-like  processes  [inner  hair-cells). 
External  and  almost  parallel  to  the  outer  group  are  four  or 
five  rows  of  hair-cells  {outer  hair-cells)  which  are  attached  to  the 
basilar  membrane,  while  their  other  extremity  projects  as  a  brush 
of  hairs  through  the  reticular  membrane  (membrane  of  Kulliker). 
This  latter  membrane  is  a  very  delicate  framework,  perforated 
with  holes,  through  which  the  hairs  of  the  outer  hair-cells  project, 
and  which  extends  from  the  inner  rods  to  the  external  row  of  hair- 
cells.  It  acts  as  a  support  for  the  ends  of  these  cells.  The  inter- 
val between  the  outer  hair-cells  and  the  spiral  ligament  is  occupied 
by  cells  of  a  columnar  form  (the  sujpporting  cells  of  Hensen).  The 
organ  of  Corti  is  covered  over  and  separated  from  the  endolymph 
of  the  ductus  cochlearis  by  the  so-called  membrana,  tectoria. 

§  30.  The  problem  before  the  labyrinth  of  the  ear  is  in  part  the 
same  as  that  solved  by  the  tympanum,  namely,  the  problem  of  con- 
veying the  acoustic  waves  to  the  true  end-apparatus  of  hearing. 
The  repeated  shocks  of  the  stirrup  at  the  fenestra  ovalis — and  per- 
haps, in  far  less  degree,  the  pulsations  of  air  at  the  fenestra  ro- 
tunda— produce  waves  in  the  fluid  of  the  labyrinth.  Any  mole- 
cular oscillations  of  this  fluid,  thus  occasioned,  cannot,  however, 
act  directly  as  the  appropriate  stimulus  of  the  sensations  of  sound. 
Since  the  dimensions  of  the  whole  mass  thrown  into  vibration  are 
so  small  in  comparison  with  the  length  of  the  acoustic  Avaves  that 
the  extension  of  the  shock  from  the  stirrup  would  be  practically 
instantaneous  tln-oughout,  and  since  the  surrounding  walls  may  be 
regarded  as  absolutely  immovable  by  any  such  impact,  the  laby- 
rinth-water would  act  as  an  incompressible  fluid.  It  would,  there- 
fore, be  unsuitable  for  the  transmission  of  various  kinds  of  acoustic 
waves.  But  different  parts  of  the  labyrinth  are  capable  of  yielding 
to  the  waves  in  the  fluid  caused  by  the  repeated  shocks  of  the 
stirrup.  Four  such  places,  into  which,  as  they  yield,  the  fluid  of  the 
labyrinth  can  retreat  (as  it  were)  are  designated  by  Hensen  ; '  these 
are  the  two  openings  of  the  aqueduct  of  the  vestibule,  the  mem- 
branes of  the  aqueduct  of  the  cochlea,  the  pores  of  the  blood-vessels 
in  the  bone,  the  membrane  of  the  fenestra  rotunda  by  bulging  out 
into  the  tympanic  cavity.  Impulses  started  in  the  fluid  of  the 
labyrinth  would  thus  result  in  its  movement  back  and  forth,  so  as 
to  produce  a  friction  of  the  end-apparatus.  This  friction  would 
be  increased  by  the  action  of  the  otoliths,  or  minute  calcareous 
particles,  found  in  the  fluid.  Thus  the  waves  started  at  the  fenes- 
tra ovalis  would  be  diffused  over  the  vestibule  and  into  the  scala 
vestibuli  of  the  cochlea,  where  they  would  flow  to  its  head,  being 
'  In  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  106. 


THE   ATSTALTSTS   OF   SOUKDS.  195 

prevented  by  the  separating  membrane  from  entering  the  scala 
tj'inpaui.  To  what  extent  these  waves  flow  through  the  helico- 
trema,  or  small  hole  at  the  apex  of  the  cochlea,  into  the  scala  tjm- 
pani,  and  wliat  are  the  exact  relations  between  the  waves  in  this 
latter  scala  and  those  in  the  scala  vestibuli — cannot  be  stated  con- 
fidently. Nor  can  the  exact  part  of  the  basilar  membrane  at  which 
the  excitation  of  the  end-organs  by  the  oscillations  of  the  structure 
begins,  be  indicated  with  certainty.  This  membrane  is,  however, 
undoubtedly  thrown  into  vibration  through  the  unequal  pressure 
of  the  moving  fluid  ;  and  by  its  vibration  it  excites  the  nervous 
structures  Avith  which  it  is  intimately  connected. 

§  31.  A  still  more  difficult  problem  for  the  labyrinth  to  solve 
may  be  described  in  one  word  as  a  problem  of  "analysis."  The 
inner  ear  is  not,  indeed,  contrived  so  as  to  reproduce  changes  in 
the  form  of  the  acoustic  oscillations,  as  such,  after  the  manner  in 
which  these  changes  can  be  made  apparent  to  the  eye  or  to  touch. 
But  all  our  analogies  for  the  analysis  of  composite  tones — the 
"  clangs  ■'  or  musical  notes  of  ordinary  experience — are  derived  from 
the  process  of  sympathetic  vibrations.  We  are  led,  then,  to  inquire 
whether  any  part  of  the  structure  of  the  ear  is  capable  of  enough 
such  sympathetic  vibi'ations  to  account  for  the  experience  which 
we  have  in  recognizing  all  the  possible  degrees  of  pitch  in  the  scale 
of  musical  sounds.  The  structure  must  also  be  such  as  to  receive 
the  impressions  produced  by  a  number  of  simultaneous  tones,  com- 
posing a  harmony.  Moreover,  it  must  be  such  as  to  represent 
tones  that  follow  each  other  in  rapid  succession,  as  do  the  notes  of 
a  melody.  The  sympathetic  vibratory  apparatus  of  the  labyrinth 
must  therefore  cease  its  vibrations  immediately  upon  the  cessation 
of  the  sounds  in  sympathy  with  which  it  vibrates.  In  other  words, 
it  must  either  have  a  damper,  or  be  so  constructed  as  to  return 
at  once  to  a  state  of  rest  without  such  a  damper.  It  must  be  capa- 
ble of  being  thus  excited,  and  of  returning  to  a  state  of  rest,  no 
fewer  than  five  hundred  times  in  a  second,  since  the  crackling 
of  electric  sparks,  between  which  the  interval  is  no  more  than  .002 
of  a  second,  can  be  heard  as  distinct  noises.  Still  further,  the  end- 
apparatus  of  hearing  must  suffice  for  all  kinds  of  noise,  as  distin- 
guished from  musical  (ones  ;  and  it  is  extremely  difficult  to  see  how 
the  same  apparatus  which  serves  for  the  analysis  of  the  clang  can 
also  suffice  for  all  the  various  sensations  of  noise. 

The  manner  is  not  known  in  which  the  auditory  hairs  and  stones 
and  cells  of  the  vestibule  and  ampuUse,  and  the  rods  of  Corti,  the 
fibres  of  the  basilar  membrane,  and  the  conical  hair-cells  of  Dei- 
ters,  in  the  cochlea,  actually  discharge  the  required  functions.    The 


196  THE   HUMAN   EAE. 

structure  of  the  end-apparatus  in  the  vestibule  and  semicireulai: 
canals  is  plainly  not  adapted  to  the  analysis  of  musical  tones.  The 
otoliths  found  in  the  vestibule,  and  the  hairs  of  the  ampullse,  are 
not  capable  of  regular  sympathetic  vibrations  ;  moreover,  they  form 
no  scale  of  structures  corresponding  to  the  scale  of  sensations  of  toue. 
This  fact  has  led  to  the  assumption  that  these  organs  are  designed  to 
act  as  the  end-organs  of  noise  instead  of  musical  sound.  The  more 
complicated  structures  of  the  ductus  cochlearis  do  seem,  on  the 
contraiy,  to  be  adapted  for  the  required  analytic  functions.  It  was 
first  argued  by  Helmholtz  that  the  bov^s  formed  by  the  rods  or 
fibres  of  Corti  are  enough  in  number  to  constitute  such  a  scale  of 
structures  that  this  work  of  analysis  can  be  assigned  to  them. 
Some  three  thousand  of  these  fibres,  arranged  in  rows  upon  the 
basilar  membrane  hke  the  keys  of  a  piano-forte,  if  distributed  over 
seven  octaves  would  give  about  thirty-three  for  a  semitone.  They 
might  then  be  supposed  to  be  elastic  ;  and  since  they  differ  in 
size,  to  be  tuned  for  particular  sounds,  so  that  the  sympathetic 
vibration  of  each  one  of  them  cori-esponds  to  the  sensation  of  a 
given  toue.  But  the  rods  of  Corti  are  stiff  and  not  easily  vibratory  ; 
and  their  office  is  probably  simply  to  constitute  a  support  for  the 
hair-cells.  Moreover,  birds,  which  are  undoubtedly  capable  of  ap- 
preciating musical  notes,  have  no  rods  of  Corti. 

Hen  sen  has  shown  '  that  the  basilar  membrane  is  itself  in  a  good 
degree  gi'aded  to  pitch  ;  its  continuous  structure  and  expansion  in 
size  from  the  beginning  to  the  end  of  the  ductus  cochlearis  en- 
courage the  assumption  that  its  individual  radii  act  like  stretched 
strings  to  respond  to  the  different  tones,  from  the  lowest  to  the 
highest.  The  calculations  of  Helmholtz  have  tended  to  confirm  the 
view  of  Hensen..  It  is  assumed,  then,  that  the  parts  resting  upon 
this  membrane  would  be  moved  up  and  down,  and  that  the  excita- 
tion of  the  conical  hair-cells — with  which  the  terminal  fibrils  of  the 
auditory  nerve  are  supposed  to  be  connected — is  thus  brought 
about.  The  number  of  the  acoustic  cells  is  claimed  to  be  about 
great  enough  to  correspond  to  the  demands  made  upon  the  organ 
which  shall  be  instrumental  in  the  physical  analysis  required  as  a 
basis  for  the  sensations  of  musical  tones.  The  claim  is  at  best 
doubtful.  As  Hensen  himself  remarks,^  the  possibility  is  by  no 
means  excluded  that  the  working  of  this  complicated  and  delicate  ap- 
paratus may  be  altogether  different  from  that  conjectured  by  all  such 
theory.  In  other  words,  the  physiology  of  the  peripheral  mechanism 
of  hearing  is  as  yet  in  a  very  incomplete  and  unsatisfactory  state. 

1  Zeitschrift  f.  wiss.  Zool.,  XIII.,  p.  481  f. 

2  In  Hermaun's  Ilaudb.  d.  Physiol.,  III.,  ii.,  p.  104  f. 


EISTD-OEGANS   OF   MOTIOTST.  197 

8  32.  A  brief  description  of  the  End-Organs  of  Motion,  or  motor 
end-plates,  will  suffice  for  our  purposes.  In  general,  the  termina- 
tions of  the  efferent  nerves  are  connected  either  with  electrical 
organs  (as,  for  example,  in  the  torpedo),  or  with  secretory  glands, 
or  with  the  muscular  fibre.  We  consider  only  the  last  of  these 
three  cases. 

After  an  efferent  nerve  has  entered  the  substance  of  the  so-called 
voluntary  or  striated  muscle,  it  subdivides  among  the  individual 
muscular  fibres,  separating  these  fibres  from  each  other.  Such 
nerve-twigs  usually  lose  their  medullary  sheath,  and  their  axis- 
cylinder  splits  up  into  fibrils,  whose  exact  mode  of  termination  has 
been  much  debated.  It  appears  now  to  be  demonstrated  (by 
Kiihne,  Margo,  Eouget,  and  others)  that  the  axis-cylinder  itself 
pierces  the  sarcolemma  or  sheath  of  the  muscular  fibre  ;  that  the 
neurilemma  becomes  continuous  with  the  sarcolemma  ; '  and  that 
the  fibrils,  into  which  the  axis-cylinder  divides,  form  a  flat,  branch- 
ing mass  within  certain  peculiar,  disk-shaped  bodies  situated  inside 
the  sarcolemma,  and  called  "motor  end-'plates.'"  In  the  non-striated 
(or  non-voluntary)  muscles,  the  nerves  divide  and  subdivide  to  form 
more  and  more  minute  plexuses  of  nerve-fibres,  which  are  distrib- 
uted in  the  connective  tissue  that  separates  the  muscular  fibres  from 
each  other.  The  exact  relation  between  this  extremely  minute  in- 
tramuscular network  of  fibrils  and  the  nuclei  of  the  cells  of  mus- 
cular "fibre  "  is  not  yet  made  out. 

The  shape  and  structure  of  the  motor  end-plates  are  different  for 
different  animals,  and  even  for  different  muscles  of  the  same  ani- 
mal. Indeed,  the  mode  of  the  termination  of  the  motor  nerves  in 
the  muscle  appears  to  be  somewhat  distinctive  of  the  different 
parts  of  the  muscular  structure.  Sometimes  the  axis-cylinders  are 
somewhat  enlarged,  with  strongly  granular  corpuscles  attached  or 
adjacent.  Sometimes  a  granular  mass  with  its  nuclei  forms  a  kind 
of  base  or  floor  for  the  terminal  nerve-fibres  ;  and  this  eminence 
may  be  elongated,  elliptical,  or  circular.  But  the  character  and 
variety  of  these  forms  are  of  no  particular  interest  to  psychology, 
even  as  approached  from  the  physiological  point  of  view. 

'  The  question  of  histology  is  debated,  whether  the  neurilemma  actually 
becomes  continuous  with  the  sarcolemma.  Strictly  speaking,  according  to 
Kiihne,  it  does  not ;  but  then,  strictly  speaking,  it  is  not  continuous  with  it- 
self. It  is,  as  we  have  seen  (p.  36  f),  divided  by  the  annular  constrictions  into 
members  which  are  separate  structures.  It  is  to  be  considered  as  fringed 
out  on  its  edge  and  cemented  to  the  sarcolemma  [See  on  this  subject  the 
monograph.  Die  Verbindung  d.  Nervenscheiden  mit  dem  Sarkolemm,  Sepa- 
ratabdruck  aus  der  Zeitschrift  fiir  Biologie,  by  Kiihne.] 


CHAPTEK  YI. 
THE  DE^TELOPMENT   OF  THE  NERVOUS  MECHANISM. 

§  1.  The  life  of  the  individual  man,  so  far  as  it  can  be  made  an 
object  of  immediate  observation  and  scientific  description  begins 
as  an  undifferentiated  germ,  "without  apparent  distinction  of  bodily 
organs  or  of  physical  and  psychical  activities.  This  living  germ 
undergoes  a  development.  Before  it  can  be  subjected  to  ordinary 
inspection  it  has  unfolded  itself  into  an  elaborate  organism  ;  and, 
in  its  normal  relation  to  the  other  sj'stems  of  this  organism  (mus- 
cular, respiratory,  metabolic,  reproductive,  etc.),  the  nervous  system 
has  acquired  all  its  complex  mechanism,  consisting  of  an  indefinite 
number  of  parts.  Wliat  are  the  different  stages  of  the  development 
of  this  nervous  system,  and  what  are  the  laws  according  to  which 
its  different  factors  and  organs  become  differentiated,  it  belongs  to 
the  science  of  Embryology  to  describe.  But  it  belongs  to  psychology 
to  make  such  doubtful  inferences  as  suggest  themselves  concerning 
the  psychical  activities  that  are  to  be  ascribed  to  the  unfolding 
mind  of  the  embryo.  Psychology,  indeed,  attempts  in  such  a  case 
to  form  a  picture  of  those  earliest  and  most  obscure  mental  states, 
the  elements  of  which  can  no  longer  be  rejDroduced  or  recombined 
in  the  developed  consciousness  of  the  adult.  To  this  fact  is  due, 
in  part,  the  doubt  which  clings  to  all  such  inferences.  But  this 
doubt  is  also  due  to  the  fact  that  embryology  itself  is  so  incomplete, 
even  in  respect  to  its  possession  of  single  facts,  and  yet  more  in- 
complete in  respect  to  its  power  to  set  forth  any  system  of  general 
truths  and  laws. 

Our  knowledge  of  all  the  earlier  states  and  changes  of  con- 
sciousness is  wholly  a  matter  of  the  interpretation  of  states  and 
movements  of  the  bodily  organism,  in  terms  of  our  own  conscious 
mental  experience.  If,  then,  it  were  found  that  certain  physical  states 
and  motions  of  the  human  embryo  need  for  their  interpretation 
the  assumption  of  preceding  or  accompanying  mental  states,  we 
should  have  the  right  to  carry  our  psychological  principles  back  to 
the  life  of  this  embryo — even  back  to  its  beginning  in  the  undif- 
ferentiated   germ   from   which  the  whole  development  proceeds. 


THE   TWO-FOLD   PROCESS.  199 

But  as  the  case  now  stands,  the  proper  physical  science  cannot 
claim  to  have  furnished  us  with  the  requisite  description  of  these 
antenatal-physical  movements  and  states.  Little  use  for  the  main 
purposes  of  Physiological  Psychology,  therefore,  can  be  made  of 
facts  accessible  as  to  the  embryonic  development  of  man.  "We 
might  even  seem  warranted  in  passing  by  the  whole  subject  with 
two  or  three  general  observations  like  the  following  :  The  two-fold 
life  of  man,  both  nervous  mechanism  and  mind,  begins  in  what  is 
apparent  only  as  a  physical  unity,  in  that  system  of  moving  mole- 
cules which  constitutes  the  living  germ.  Out  of  this  unity,  and  in 
indissoluble  connection  with  it,  the  two-fold  human  life  then  pro- 
gressively develops.  The  mechanism  unfolds  itself,  increases  the 
complexity  of  its  molecular  activities,  runs  its  course  of  changes,  and 
is  broken  up  again  into  its  material  elements.  The  mind  manifests 
itself  in  primitive  activities,  unfolds  itself,  increases  the  complexity 
of  its  psychical  life,  and  then  ceases  to  make  itself  known  through 
the  physical  mechanism,  when  the  mechanism  itself  is  dissolved. 
And  all  the  while  the  molecular  mechanism  and  the  mind  are  most 
closely  and  mysteriously  correlated  in  their  development  as  a  to- 
talit}',  and  in  their  particular  activities. 

But  in  spite  of  the  fact  that  embryology  furnishes  psychology 
with  scanty  material  for  any  extended  and  trustworthy  conclusions 
with  regard  to  the  earliest  activities  and  development  of  the  mind, 
at  least  a  sketch  of  its  principal  outlines,  so  far  as  the  nervous  sys- 
tem is  concerned,  seems  desirable.  Of  knowledge  fi*om  direct  ob- 
servation concerning  the  early  development  of  the  human  embr^^o 
there  is  exceedingly  little.  Yet  the  comparatively  few  facts  which 
are  indisputably  known,  throw  considerable  light  upon  the  nature 
and  functions  of  the  human  nervous  mechanism.  Moreover,  in  cer- 
tain most  important  particulars  there  is  good  reason  to  believe  that 
the  earliest  history  of  the  development  of  the  embryos  of  other 
animals  is  substantially  like  that  of  the  human  embryo.  The  very 
first  things  in  the  life  of  the  chick — or  better,  one  of  the  mammals 
—for  example,  may  be  described  as  probably  holding  good  in  all 
important  respects  for  the  life  of  man.  And  when  those  diifei'ences 
wlaich  are  most  strikingly  human  begin  plainlj'^  to  appear,  they 
show  what  parts  of  the  nervous  system  are  most  worthy  of  em- 
phasis as  distinctively  connected  with  man's  mental  life.' 

§  2.  The  immature  ovarian  ovum  of  the  common  fowl — lil^e  that 

'  The  following  description  is  taken  to  a  large  extent,  and  in  some  places 
almost  verbatim,  from  Foster  and  Balfour's  Elements  of  Embryology,  London, 
ly83,  and  F.  M.  Balfour,  Comparative  Embryology,  vol.  ii. ,  pp.  177  ff.,  Lon- 
don, 1881. 


200  EMBRYONIC   LIFE   OF   MAN. 

of  every  other  animal — presents  the  characters  of  a  simple  cell.  It 
is  seen  to  consist  of  a  naked  protoplasmic  body  which  contains  in 
its  interior  a  nucleus  (the  germinal  vesicle)  and  within  this  a  nucle- 
olus (the  germinal  sjjot).  It  is  enclosed  in  a  capsule  of  epithelium, 
called  the  "follicle,"  or  "follicular  membrane."  As  the  ovum  ma- 
tures, the  body  of  it  grows  in  size  and  a  number  of  granules  make 
their  appearance  in  the  interior ;  while  the  outermost  layer  of  the 
protoplasm  remains  free  from  them.  But  as  the  granules  grow 
larger  in  the  centre,  other  granules  appear  also  in  the  periphery 
of  the  ovum.  The  germinal  vesicle,  during  the  growth  of  the  ovum, 
travels  toward  the  periphery  where  the  protoplasm  surrounding- 
it  i-emains  comparatively  free  from  granules.  Accessory  germinal 
spots  make  their  appearance.  The  cells  of  the  follicular  membrane, 
which  were  at  first  arranged  in  a  single  row,  now  become  two  or 
more  rows  deep ;  and,  whereas  the  immature  ovum  is  naked,  its 
superficial  layer  is  now  converted  into  a  radiately  striated  mem- 
brane. Still  later,  a  second  membrane  appears  between  this  striated 
membrane  and  the  cells  of  the  follicle ;  and  the  former  disappear- 
ing as  the  ovum  approaches  maturity,  the  second  membrane  (called 
the  "vitelline")  remains  alone.  Other  changes  which  take  place 
after  the  ovum  has  ripened  and  has  been  discharged  into  the  ovi- 
duct, it  is  not  necessary  to  describe.  They  result  in  the  formation 
of  the  accessoi-y  parts  of  the  egg.  The  only  essential  constituent 
of  the  body  of  the  ovum  is  an  active  living  protoplasm. 

§  3.  Impregnation  takes  place  in  the  upper  portion  of  the  oviduct, 
and  consists  in  the  entrance  of  a  single  spermatozoon  into  the 
ovum,  followed  by  the  fusion  of  the  two.  The  spermatozoon  itself 
may  be  considered  as  a  cell,  the  nucleus  of  which  is  its  head.  On 
entering  the  ovum,  the  substance  of  its  tail  becomes  mingled  with 
the  protoplasm  of  the  ovum ;  while  the  head  enlarges,  moves  to- 
ward and  fuses  with  a  part  of  the  substance  of  the  ovum,  thus 
constituting  the  nucleus  of  the  impregnated  e^Q.  In  this  manner 
the  jDhysical  and  mental  peculiarities  of  both  parents  are  trans- 
mitted or  carried  over  to  the  offspring  by  means  of  the  actual  fu- 
sion of  substance  derived  from  the  bodies  of  both. 

§  4.  A  process  known  as  segmentation  or  "yolk-cleavage"  follows 
the  fecundation  of  the  ovum.  This  process  consists  in  a  succes- 
sive division  of  the  ovum  into  a  number  of  cells,  from  which  all  the 
cells  of  the  full-grown  animal  are,  as  it  were,  the  lineal  descendants. 
This  process  has  many  variations  among  the  different  animals. 
The  chief  peculiarity  among  the  mammals  is  that  the  whole  mass  of 
the  yolk  is  subject  to  this  change. 

By  segmentation  the  germinal  disk  of  the  ovum  is  broken  up 


THE   OVARIAlSr   OVUM. 


201 


into  a  large  number  of  rounded  segments  of  protoplasm,  called  the 
blastoderm.  Of  these  segments  those  that  lie  uppermost  are  smaller 
than  those  beneath.  The  beginning  of  the  two  layers  into  which 
the  blastoderm  divides  is  thus  made.  The  behavior  of  the  nucleus 
formed  by  the  union  of  substance  from  the  male  and  the  female, 
during  the  process  of  segmentation,  has  not  been  so  satisfactorily 
traced  ;  it  appears  probable,  however,  that  a  pi'ocess  of  division  goes 
on  in  it  also.  Other  nuclei,  thought  to  be  derived  from  the  primi- 
tive nucleus,  make  their  appearance  immediately  below  the  blasto- 
derm. The  distinction  between  the  upper  and  lower  layers  of  the 
blastoderm  now  becomes  more  obvious,  for  the  segments  of  the 
former  arrange  themselves  side  by  side,  with  their  long  axes  vertical, 
as  a  membrane  of  columnar  nucleated  cells ;  while  those  of  the 
latter  continue  granular  and  round,  and  form  a  close,  irregular 
net-work  of  cells,  whose  nuclei  are  not  easily  seen. 

§  5.  The  principal  difference  between  the  ovum  of  a  mammal  and 
that  of  a  bird  depends  upon  the  amount  and  distribution  of  the 
food-yolk.  The  ovum  of  the  mammal  is  small — the  human  ovarian 
ovum  being  only  from 
t\s  ^^  -ih  of  an  inch 
in  diameter — because 
it  contains  so  little 
food-yolk  ;  but  this 
small  supply  is  dis- 
tributed uniformly 
throughout.  In  con- 
sequence of  the  above- 
mentioned  difference, 
the  ovum  is  able  to 
break  up  into  seg- 
ments    through     the 

whole  of  its  protoplasmic  mass.  As  the  process  of  segmentation 
goes  on,  the  differences  among  the  ova  of  different  species  of  ani- 
mals become  more  clearly  marked.  For  example,  in  the  rabbit, 
although  the  details  are  differently  described  by  different  observers, 
at  the  close  of  the  process  of  segmentation  the  ovum  appears  to  be 
comj)osed  of  "  an  outer  layer  of  cubical  hyaline  cells,  almost  en- 
tirely surrounding  an  inner  mass  of  highly  granular,  rounded,  or 
polygonal  cells."  In  a  small  circular  area,  however,  the  inner  mass 
remains  exposed.  The  outer  cells  soon  close  over  the  exposed  spot 
(called  by  van  Beneden,  hlaatopore),  and  thus  form  a  superficial 
layer.  A  narrow  cavity  then  appears  between  the  two  layers, 
which  extends  so  as  to  separate  them  completely,  except  in  the 


Fig.  Tl. 


Fig.  72. 


[GS.  71  and  73.— Fructified  Human  Egg  of  12-1.3  days,  seen 
from  the  surface  and  the  side.  In  the  centre  o£  the  former  is 
what  Keichert  considers  the  embryonic  area. 


202  EMBKYONIC   LIFE   OF   MAN. 

region  near  to  the  spot  originally  exposed.  The  enlargement  of 
the  ovum  and  of  the  cavity  together,  soon  give  the  whole  structure 
the  appearance  of  a  vesicle  with  a  thin  wall  and  a  large  central 
cavity.  This  vesicle  is  called  the  blastodermic  vesicle.  The  greater 
part  of  its  walls  is  composed  of  a  single  row  of  outer  flattened 
cells  ;  while  an  inner  lens-shaped  mass  of  cells  appears  attached  to 


Fig.  73. — Vascular  Area  and  Embryonic  Area  of  the  Embryo  of  a  Babbit,  seven  days  old.  ^^j^, 
(Kolliker.)  o  o,  the  vascular  or  opaque  area ;  ag,  embryonic  area;  pr,  primitive  streak  and 
groove ;  rf,  medullary  groove. 

a  portion  of  the  inner  side  of  the  outer  layer.  The  "  blastodermic 
vesicle  "  enlarges  rapidly  ;  its  inner  mass  of  cells  loses  its  lens-like 
shape,  becomes  flattened,  and  spreads  out  on  the  inner  side  of  the 
outer  layer.  Its  central  part  remains  thicker  and  forms  an  opaque 
circular  spot  on  the  blastoderm,  which  is  the  beginning  of  the  area 
where  the  embryo  is  to  fol-m  (the  embryonic  area). 

§  6.  The  immediately  subsequent  history  of  the  development  of 
the  mammalian  ovum,  until  the  appearance  of  the  so-called  "primi- 
tive streak,"  is  less  perfectly  understood :  Foster  and  Balfour  '  speak 
of  the  following  description  as  "tentative."  In  the  embryonic 
area  the  cells  of  the  inner  mass  become  divided  into  two  distinct 
strata,  an  upper  one  of  i-ounded  cells  which  lies  close  to  the 
flattened  outer  layer,  and  a  lower  one  of  flattened  cells  (the  "hypo- 

'  Elements  of  Embryology,  p.  316  f. 


THE  THREE  GERMINAL  LATEPwS. 


203 


blast").  The  former  becomes  fused  with  the  outer  layer,  and 
thus  gives  rise  to  a  layer  of  columnar  cells  (the  "  epiblast ").  In 
this  way  the  embryonic  area  consists  of  two  layers  of  cells  ;  the 
upper  one  of  which  is  the  epiblast,  and  the  under  one  the  hypoblast. 

The  blastoderm  at  first,  then,  consists  of  only  two  layers,  which 
constitute  a  double-walled  sac  (the  gastrula)  ;  but  a  third  layer 
soon  makes  its  appearance  between  the  other  two.  These  three 
l^jevB— epiblast,  mesoblast,  and  hypoblast— are  called  "germinal 
layers  "  and  are  found  in  the  embryos  of  all  forms  of  vertebrate, 
and  most  forms  of  invertebrate  animals.  The  middle  one,  or  meso- 
blast, arises  from  certain  parts  of  the  other  two  primitive  layers,  in 
a  manner  which  need  not  be  described.  From  these  three  germi- 
nal layers,  all  the  different  parts  of  the  organism  of  the  animal  are 
developed.  The  history  of  the  development  of  every  animal  in  its 
earlier  stages  is,  therefore,  a  narrative  of  the  changes  which  take 
place  in  the  three  layers  of  the  blastoderm.  The  hypoblast^  is 
the  secretory  layer  ;  and  from  it  almost  all  the  epithelial  hning 
of  the  alimentary  tract  and  its  glands  is  derived.  The  mesoblast 
is  the  source  of  "the  skeletal,  muscular,  and  vascular  systems,  and 
of  the  connective  tissue  of  all  the  parts  of  the  body.  But  it  is  the 
epiblast  which  produces  the  central  and  peripheral  nervous  system, 
the  epidermis,  and  all  the  most  important  parts  of  the  organs  of 
sense.  It  is  to  the  development  of  the  epiblast  exclusively,  then, 
that  we  now  direct  our  attention. 

§  7.  The  process  of  differentiating  the  layers  of  the  embryo  is 
intimately  connected  with  another,  which  results  in   forming   a 


Fig  ''4  -Primitive  Stroak  of  the  Embryo  of  a  Rabbit,  eight  days  and  nine  hoiars  old.  22"/,. 
(Kmliker)  No  medullary  groove  has  yet  been  formed,  ax,  primitive  streak:  pr  primitive 
groove  f;;/,  primitive  fold  ;  ect,  ectoderm  (or  epiUast) ;  mes,  mesoderm  (or  mesoblast) ;  ent,  en- 
toderm {hypoblast). 

structure  known  as  the  primitive  groove.  This  process  is  substan- 
tially alike  in  mammals  and  in  birds.  A  short  sickle-like  thickening 
of  the  blastoderm,  which  afterward  becomes  a  "  narrow  strap-like 
opacity"— due  to  a   forward  propagation  (linear  proliferation)  of 


204  EMBEYONIC   LIFE   OF   MAN. 

epiblast  cells  in  a  straight  line — arises  near  the  junction  between 
the  pellucid  and  the  opaque  areas  of  the  blastoderm,  and  stretches 
inwai'd  upon  the  embryonic  area ;  it  is  called  the  primitive  streak. 
The  median  line  of  the  primitive  streak  then  shows  a  shallow  fur- 
row, running  along  its  axis.  This  furrow  is  called  the  primitive 
groove.     (Compare  Fig.  73.) 

§  8.  Now  occurs  the  formation  of  the  medullary  groove.  In  that 
portion  of  the  embryonic  area  which  is  in  front  of  the  primitive 
streak,  the  axial  pai't  of  the  epiblast  thickens  ;  two  folds  arise  along 
the  boundaries  of  a  shallow  median  groove  ;  the  folds  meet  in  front, 
diverge  behind,  and  then  enclose  between  them  the  front  part  of  the 
primitive  streak.  These  are  the  medullary  folds,  and  they  constitute 
the  first  definite  features  of  the  embryo.  The  part  bounded  between 
these  folds  is  called  the  "  medullary  plate  ;  "  its  supreme  impor- 
tance in  the  embryo  ajopears  in  the  fact  that  it  is  the  portion  of  the 
epiblast  which  gives  rise  to  the  central  nervous  system.  At  about 
the  time  of  the  development  of  the  medullary  groove  (a  little  earlier) 
an  important  change  is  taking  place  in  the  constitution  of  the 
hypoblast  in  front  of  the  primitive  streak.  An  opaque  line  ap- 
pears, as  seen  from  the  surface,  and  is  continued  forward  from  the 
front  end  of  the  streak,  but  stops  short  at  a  semicircular  fold  near 
the  front  part  of  the  pellucid  area.  This  fold  is  the  future  head- 
fold  of  the  embryo.  The  opaque  line  is  due  to  a  concentration  of 
cells  in  the  form  of  a  cord  ;  it  is  the  beginning  of  what  is  known  as 
the  nolochord.  It  is  to  subsequent  changes  in  connection  with  the 
notochord  that  we  are  to  look  for  the  development  of  the  distinct- 
ively vertebral  structure  of  the  animal. 

§  9.  From  this  point  onward  the  shaping  of  recognizable  parts 
of  the  embryo  proceeds  rapidl}'.  The  pellucid  area,  which  was  at 
first  quite  flat  or  slightly  curved,  has,  in  the  process  of  its  growth, 
suffered  a  "  tucking  in  " — as  it  were — ^of  a  portion  of  the  blasto- 
derm, in  the  form  of  a  crescent.  It  is  this  tuck  which,  when  viewed 
from  above,  appears  as  a  curved  line  marking  the  margin  of  the 
medullary  groove.  Thus  the  blastoderm  is  at  this  spot  folded  in 
the  form  of  the  i-eversed  letter  8  ;  the  fold  is  the  one  already  re- 
ferred to  as  the  "head-fold."  Of  the  two  limbs  of  this  8-fold, 
the  upper  is  continually  growing  forward  and  the  lower  is  contin- 
ually growing  backward.  As  the  head-fold  enlarges  rapidly,  the 
crescentic  groove  becomes  deeper  ;  and  at  the  same  time,  the  over- 
hanging margin  of  the  groove  rises  up  above  the  level  of  the  blasto- 
derm. The  medullary  folds  meantime  increase  in  height  and  lean 
over  from  either  side  toward  the  middle  line.  They  soon  come  in 
contact  in  the  region  which  will  afterward  become  the  brain,  and 


FIRST   CEREBRAL   VESICLE. 


205 


thus  form  a  tubular  canal  (the  medullary  or  neural  canal),  although 
they  do  not  for  some  time  coalesce.  As  the  upper  limb  or  head  of 
the  embryo  becomes  more  prominent,  the  medullary  folds  close 
rapidly,  and,  in  the  region  of  the  head  quite  coalesce.  The  open 
medullary  groove  is  thus  converted  into  a  canal  or  tube,  which  is 
closed  in  front  but  remains  open  behind.     The  fi-out  end  of  this 


Fig.  75. — Pore-part  of  an  Embryo-chirk  at  the 
end  of  the  second  day,  viewed  from  the  Dorsal 
Side.  'I/,.  (Kolliker.)  V h.  fore-brain  ;  A  b  I. 
occular  vesicles  ;  JIh.  mid-brain :  /?/*,  hind- 
brain  :  /T,  part  of  the  heart  seen  bulginsr  to 
the  rig'ht  side;  Vom.  vitelline  veins;  J/"*', 
medullary  canal,  spinal  part  ;  Mr',  raednllary 
wall  of  the  mid-brain  ;  U  w,  proto-vertetral 
somites. 


Fig.  76 — Embryo  of  a  Rabbit,  eight  days  and 
fourteen  hours  old.  ^-'"/j  (Kolliker.)  a  p. 
pellucid  area ;  v.  anterior  edge  of  the  circuit 
of  the  head;  A',  fnre-brain  ;  //',  region  of 
later  mid-brain  ;  h'",  position  of  the  hinder 
brain  ;  hz,  po.sition  of  the  heart ;  rf,  medullary 
groove  ;  I'lr,  medullary  ridge ;  uw.  meso- 
blastic  somite;  pz,  lateral  zone  ;  si?,  vertebral 
zone. 


neural  canal — having  a  more  rapid  grovrth  than  the  rest — dilates 
into  a  small  bulb  or  vesicle,  the  ca\ity  of  which  remains  continuous 
with  that  of  the  rest  of  the  canal,  while  its  walls  are  similarly  formed 
of  epiblast.  This  bulb  is  the  so-called  first  cerebral  vesicle ;  and  the 
lateral  processes  which  soon  grow  out  from  its  sides  are  called  optic 
vesicles.  Behind  the  first  vesicle,  a  second,  and  afterward  behind  the 
second  vesicle,  a  third  is  soon  formed.   Thus  these  three  brain-buds, 


206 


EMBEYONIC    LIFE    OF   MAN. 


Hincl-hrain 

Rudimentary 
cerehellum 
&  medulla 


or  germinal  Drains,  are  made.  At  the  level  of  the  hind  end  of  the 
head,  two  shallow  pits  appear  (the  auditory  piti^)  which  are  the  rudi- 
ments of  the  organ  of  hearing.  Thus  the  closing-up  of  the  medul- 
lary canal  has  converted  the  original  medullary  groove  into  a 
neural  tube  ;  and  three  cerebral  vesicles  have  been  grown  which 
are  to  develop  into  the  fore-brain,  the  mid-brain,  and  the  hind- 
brain. 

§  10.  The  most  important  changes  which  now  take  place  in 
the  development  of  the  nervous  mechanism,  are  connected  with 
the  growth  of  the  three  cerebral  vesicles  and  with  the  flexure  of 
the  medullary  canal.  The  front  portion  of  this  canal— that  is,  the 
fore-brain  with   its   vesicles — in    consequence  of    inequalities   of 

growth  in  the  different 
parts  of  the  brain,  be- 
comes bent  downward  ; 
this  is  the  commence- 
ment of  the  cranial  flex- 
ure. As  the  flexure  pro- 
gresses, the  front  portion 
becomes  more  and  more 
folded  down,  so  that  the 
second  vesicle,  or  mid- 
brain, comes  to  project  in 
front  of  it.  From  the 
front  part  of  the  fore- 
brain  the  vesicles  of  the 
cerebral  hemispheres 
grow  out  and  swell  lat- 
erally, so  as  to  make  two 
buds  corresponding  to 
the  two  hemispheres  of 
the  brain.  Each  of  these  side-buds  has  a  cavity  which  is  continu- 
ous behind  with  the  cavity  of  the  fore-brain  ;  each  cavity  becomes  a 
lateral  ventricle  of  the  brain.  The  original  vesicle  of  the  fore-brain, 
having  ceased  to  occupy  its  front  position,  is  developed  into  the 
parts  surrounding  the  third  ventricle.  In  the  hind-brain,  or  third 
cerebral  vesicle,  the  part  nearest  to  the  mid-brain  becomes  marked 
off  by  a  constriction  ;  the  hind-brain  is  thus  separated  into  two 
parts  — the  rudimentary  cerebellum  with  the  pons  in  front,  the 
rudimentary  medulla  oblongata  behind. 

§  11.  Various  differentiations  of  the  lining  of  the  epiblast,  which 
is  involuted  along  the  cerebro-spinal  cavity,  take  jDlace.  Through 
the  length   of  the  neural  canal  this  lining  is   thickened  at   each 


Plexus 
chorioidc. 


Foramer 
Monroi 


N.  trig. 


Fig.  77. — 4,  Brain  of  an  Embryo  of  the  Rabbit.  B,  Brain 
of  an  Embryo  of  the  Ox.  In  both  cases  the  side-wall  of 
the  left  hemisphere  is  removed.     (After  Mihalkovics.) 


CRANIAL   AISTD   SPHSTAL   ISTERVES.  207 

side,  so  that  tlie  cavity  is  no  longer  circular,  but  resembles  a  narrow 
vertical  slit.  In  the  region  of  the  cerebral  hemispheres  the  sides 
and  floor  of  the  canal  are  much  thickened,  but  in  the  region  of 
the  third  and  fourth  ventricles,  its  roof  becomes  excessively  thin, 
^  so  as  to  foi-m  a  membrane  consisting  of  scarcely  more  than  a  single 
layer  of  cells. 

§  12.  Another  important  event,  at  about  this  stage  in  the 
development  of  the  embryo,  is  the  formation  of  the  cranial  and 
spinal  nerves.  The  cranial  nerves  sprout  out  of  a  continuous 
band  (the  neural  band),  composed  of  two  plates,  which  connects 
the  dorsal  edges  of  the  neural  canal  with  the  external  epiblast. 
This  band  separates  from  the  epiblast  and  becomes  a  crest  on  the 
roof  of  the  brain,  with  its  two  plates  fused  together.  The  crest 
extends  forward  as  far  as  the  roof  of  the  mid-brain.  As  the  roots 
of  the  cranial  nerves  grow  centrifugally  and  become  established, 
the  crest  connecting  them  is  partially  obliterated.  The  posterior 
roots  of  the  spinal  nerves  are  outgrowths  of  a  series  of  median 
processes  of  cells  that  appear  on  the  dorsal  part  of  the  cord.  These 
outgrowths  are  symmetrically  arranged,  and  attached  to  the  walls 
of  the  cord  ;  but  their  original  attachment  is  not  permanent.  Such 
rudimentary  posterior  spinal  nerves  divide  subsequently  into  three 
portions— a  rounded  portion  nearest  to  the  cord,  an  enlarged 
middle  portion  forming  the  rudiment  of  a  ganglion,  and  a  periphe- 
ral portion  forming  the  commencement  of  the  nerve.  The  origin 
of  the  anterior  roots  of  the  spinal  nerves  is  less  satisfactorily  made 
ou^. 

§  13.  In  the  further  development  of  the  hind-brain  the  medulla 
oblongata  undergoes  changes  of  a  somewhat  complicated  character. 
Its  roof  becomes  extended  and  thinner  ;  where  the  two  lateral  halves 
of  the  brain  were  at  first  united  (at  the  raphe)  a  separation  takes 
place,  so  that  the  sole  union  of  the  two  sides  is  by  a  single  row  of 
cells.  The  thin  roof  of  the  fourth  ventricle  is  thus  formed.  The 
floor  of  the  whole  hind-brain  becomes  thickened,  and  on  its  outer 
surface  a  layer  of  longitudioal  non-medullated  nerve-fibres  appears. 
The  roof  of  the  anterior  part  of  the  hind-brain,  which  has  become 
thickened  instead  of  thinned  out — thus  forming  the  rudimentary 
cerebellum — is  developed,  first,  by  the  formation  of  the  median  lobe 
(or  vermiform  process)  and,  afterward,  by  the  swelling  of  its  sides  so 
as  to  constitute  the  cerebellar  hemispheres. 

§  14.  The  changes  in  the  development  of  the  mid-brain  (or 
mesencephalon)  are  comparatively  simple.  When  the  cranial  flex- 
ure has  taken  place,  the  mid-brain  is  left  at  the  front  end  of  the 
axis  of  the  body,  as  a  single  vesicle  with  a  vaulted  roof  and  a  curved 


208 


EMBRYOlSriC   LIFE   OF   MAK. 


floor,  whose  cavity  is  known  as  the  aqueduct  of  Sylvius.     The  cor- 
uora  quadrigemina  of  the  two  sides  are  marked  off  from  each  other 

by  the  appearance  of  a  vertical 
furrow  about  the  sixth  month  ; 
and  about  a  month  later  a 
transverse  depression  sepa- 
rates the  anterior  (nates)  and 
posterior  [testes)  pairs.  The 
thickening  of  the  floor  of  the 
mid-brain  gives  rise  to  the 
crura  cerebri. 

§  15.  Of  the  two  divisions 
into  which  the  fore-brain  has 
already  become  divided,  the 
posterior  constitutes  the  so- 
called       "  thalamen-eephalon." 

Pig.   78.— Head  of  the  Embryo  of  a  Sheep,   cut    Tllis  bodv  is   at    first  a    simple 
through  the  middle.     3/].     (Kiilliker.)     u,  under  ■    -,  \,  n         j.  •      m 

jaw  ;    z,  tongue  ;  s,  septum  ?iarmm  ;  occipitale    vesicle,      formed     OI       Spmule- 
basilare ;   th.   thalamus  opticus;  vt,  roof  of  the       ,  i  n  •,!  m  e 

third  ventricle:    cp.   posterior  commissure  ;  m//,     sliapcd      CellS,     Wltll      WailS     OI 
mid-brain  divided  by  a  fold  into  two  parts  ;/,  falx  -  .„  j.i  •    i  Ti„ 

cerebri  ;  /',  terminal  plate  of  the  fore-brain.     At     nearly  Unilorm  thlCkUCSS.      ItS 
the  prolongation  of  the  line  of  fm  is  the  foramen 
of  Monro,     t,  tentorium  cerebelli ;  cl,  cerebellum  ; 
pi,  plexus  of  the  fourth  ventricle. 


floor  gives  rise  to  the  optic  chiasm 
and  the  origin  of  the  optic  nerves, 
and  to  the  rudiment  of  the  infundi- 
bulum  ;  and  its  sides  become  thick- 
ened to  form  the  optic  thalami,  while 
the  interval  between  them  enlarges 
toward  the  base  and  constitutes  the 
cavity  of  the  third  ventricle.  The 
more  complicated  changes  which  its 
roof  undergoes  give  rise  to  the  pineal 
gland  and  other  small  surrounding 
structures.  It  is  the  anterior  and 
larger  portion  of  the  fore-brain  which 
constitutes  the  rudiment  of  the  cere- 
bral hemisiDheres.  In  this  cerebral 
rudiment,  also,  a  floor  and  a  roof  may 
be  distinguished.  The  former  is  de- 
veloped into  the  principal  basal  gan- 
glia, the  striate  bodies  ;  the  latter  into  the  structures  of  the  cerebral 
hemispheres  proper.  The  formation  of  the  striate  bodies  (corpora 
striata)  is  in  fact  due  to  thickenings  of  the  walls  of  the  floor  of  this 


Fig.  79  —Brain  of  Human  Embryo  of  five 
months,  with  Basal  Ganglia  laid  bare. 
Natural  size.  (Kolliker.)  st,  corpus 
striatum  ;  o,  optic  thalamus  ;  la,  ante- 
rior lobe  (lunatus)  of  the  cerebellum, 
and  Ip,  posterior  lobe  of  the  same  ;  ss, 
semiltinariR  superior,  and  si,  inferior ; 
p,  pyramid. 


DEVELOPMENT   OF   THE   BKAHS". 


209 


rudiment.  The  laying  of  the  commissures  is  the  characteristic 
feature  of  the  development  of  the  mammalian  hemispheres.  These 
Tire  the  anterior  commissure,  the  fornix, 
and  the  corpus  callosum.  But  into  the 
details  of  this  process  we  do  not  need 
to  enter.  One  characteristic  of  the  em- 
bryonic development  of  mammals  is  the 
early  enlargement  of  the  cerebral  hemi- 
spheres ;  in  the  human  embryo  they  are 
even  by  the  tenth  week  much  larger 
than  all  the  other  parts  of  the  brain. 
At  this  time  they  are  hollow  bodies 
with  comparatively  thin  upper  walls,  the 
lateral  ventricles  being  dilated  and  com- 
municating with  each  other  through  a 
wide    opening,    and    with    the    thii'd   ven- 

by   the   foramen    of  Monro.     They 

from  befoie  backward,  and  thus 
cover  up,  one  after  the  other,  the  optic 
thalami,  corpora  quadrigemina,  and  cere- 
bellum. Their  floor  keeps  on  thicken- 
ing, and.  thus  the  striate  bodies  become 
greatly  enlarged,  and  project  upward  into 
the  lateral  ventricles,  giving  these  cav- 
ities their  arched  form. 

The  following  table,  exhibits   the  rela- 
tions, with  respect  to  their  development,  in  which  the  different 
parts  of  the  brain  stand  to  its  fundamental  rudiments  : 


tricle 
grow 


Fig. 
of 


— Brain  and  Spinal  Cord 
Fcetiis,  four  months  old. 
(KOlliker.)  h,  hemispheres  of 
the  cerebrum;  m,  corpora  quad- 
rigemina (or  mesencephalon) ; 
c,  cerebellum;  too,  medulla  ob- 
longata ;  S.9,  spinal  cord  with 
its  brachial  and  crural  enlarge- 
ments. 


f  1.  Prosencephalon, 
I  Fore-brain. 


I.  Anterior  prima-  j 


xy  vesicle. 


1  2.  Tlialamencephalon, 
1^  Inter-brain. 


II.  Middle  primary  J  3.  Mesencephalon, 
vesicle.  |  Mid-brain. 

4.  Epe  ncephalon, 
J  Hind-brain. 

I  5.  Metencephalon, 
1^  After-brain. 


III.  Posterior  prima- 
ry vesicle. 


f  Cerebral  Hemispheres.  Cor- 
!  pora  Striata,  Corpus  Callo- 
j  sum.  Fornix,  Lateral  Ven- 
[  tricles,  Olfactory  bulbs, 
f  Thalami  Optici, Pineal  gland, 
J  Pituitary  body,  Third  Ven- 
[  tricle,  Optic  nerve  (prima- 
I      rily). 

f  Corpora  quadrigemina.  Crura 
)       Cerebri,  Aqueduct  of  Syl- 
)       vius.  Optic   nerve  (secon- 
l      darily). 
'  Cerebellum,     Pons    Varolii; 

anterior  part  of  the  Fourth 

Ventricle 
j  Medulla    Oblongata,  Fourth 
(       Ventricle,  Auditory  nerve. 


^  Taken  from  Quain's  Anatomy  (Ninth  Edition),  II. 
14 


p.  828. 


210 


EMBKTONIC   LIFE   OF   MAW. 


Fissura  parieto- 


Fig.  81. — Brain  of  a  Six-months  Human  Embryo.  Natural  size, 
(Kolliker.)  ol,  olfactory  bulb  ;  /«,  fissure  of  Sylvius  ;  c,  cere- 
bellum ;  p,  pons  Varolii ;  /,  flocculus  ;  o,  olive. 


The  more  important  convolutions  and  sulci  of  the  cerebral  hemi- 
spheres (those  called  "primitive  ")  result  from  the  folding  of  the 

whole  substance  of 
the  wall  of  the  hemi- 
sphere ;  the  less  im- 
portant (the  so-called 
"secondary")  consist 
merely  of  depressions 
and  elevations  of  its 
more  superficial  por- 
tion. The  former  ap- 
pear earlier — the  first 
of  the  primitive  sulci 
being  the  fissure  of 
Sylvius,  which  is  visi- 
ble before  the  end  of 
the  third  month.  By 
the  end  of  the  seventh 
month  almost  all  the  principal  features  of  the  cerebral  hemispheres, 
both  convolutions  and  sulci,  are  already  fixed. 

§  16.  The  nervous  parts  of  the  eye  are  differentiations  of  certain 
lateral  growths  of  the  germinal  brain-buds,  called  the  "optic 
vesicles."  The  optic  vesicles  are  outgrowths  from  the  sides  of  the 
first  cerebral  vesicle,  and  are  originally  connected  with  it  by  short 
and  wide  stalks  ;  at  first  they  stand  out  at  nearly  right  angles  to 
the  axis  of  the  embryo.  The  stalks  soon  become  narrower  and  thus 
form  the  rudiments  of  the 
optic  nerves  ; '  at  the  same 
time  the  rudiments  of  the 
retina  are  formed  from  the 
vesicles  themselves.  The 
bulb  of  the  optic  vesicle  is 
made  into  a  cup  with  two 
walls  by  doubling  it  upon 
itself  ;  thus  a  second  optic 
vesicle  or  "optic  cup"  is 
produced,  as  distinguished 
from  the  original  one.  The 
lens  of  the  eye  is  made  by 
thickening  some  of  the  superficial  epiblast  and  involuting  it  in- 
ward over  the  front  of  the  optic  cup,  or  secondary  optic  vesicle. 

'  But  His  and  Kclliker  suppose  these  nerves  to  be  formed  by  secondary  em- 
anation from  tlie  chiasm  or  nervous  centre. 


Fig.  82. — LouKitudinal  Sections  of  the  Eye  of  an  Embryo, 
in  three  stages.  (From  Remak.)  1,  commencement 
of  the  formation  of  the  lens,  I,  by  rlepression  of  a  part 
of  h,  the  corneous  layer  ;  u.  r,  the  primitive  ocular  vesi- 
cle is  doubled  back  on  itself  by  the  depression  of  the 
commencing  lens.  2.  the  depression  for  the  lens  is  now 
encloscil,  with  the  lens  beginnine' to  be  formed  on  tho 
inner  side:  the  optic  vesicle  is  more  folded  back.  3, 
a  third  stage,  in  which  the  secondary  ojjtic  ve.sicle,  g  I, 
begins  to  be  formed. 


.    DEVELOPMENT   OF   EYE   AISTD    EAR.  211 

This  involution  has  at  first  the  form  of  a  pit,  then  of  a  closed 
sac  with,  thick  walls,  then  of  a  solid  mass.  The  cavity  between 
the  two  walls  of  the  optic  cup  is  closed  up  by  bringing  the  walls 
into  contact.  The  subsequent  development  of  the  different  parts 
of  the  eye  is  conditioned  upon  the  fact  that  the  walls  of  the 
optic  cup  grow  more  rapidly  than  does  the  lens,  and  that  their 
growth,  does  not  take  place  equally  in  all  portions  of  the  cup.  It 
is  by  changes  in  the  surrounding  mesoblast,  which  takes  on  the 
character  of  an  investment,  that  the  outline  of  the  eyeball  is  defi- 
nitely formed  (the  choroid  and  sclerotic).  The  vitreous  humor 
also  is  a  mesoblastic  product  which  is  supposed  to  originate  as  a 
kind  of  transudation  through  the  so-called  choroid  slit.  Of  the 
two  walls,  the  inner  or  anterior  is  originally  somewhat  thicker ; 
and  since,  in  most  parts  of  the  cup  it  grows  more  rapidly,  it  con- 
stantly increases  in  relative  thickness.  But  just  in  front  of  a  line 
which  afterward  becomes  the  ora  serrata,  both  layers  soon  cease 
to  thicken  and  then  completely  coalesce  ;  thus  the  hind  portion  or 
true  retina  becomes  marked  off  from  the  ciliary  ridges  and  the  iris, 
while  the  wide  opening  of  the  optic  cup  is  narrowed  into  a  smaller 
orifice  that  constitutes  the  pupil.  By  differentiations  of  the  inner 
or  anterior  wall  of  the  hind  portion  of  the  optic  cup — its  cells  mul- 
tiplying rapidly  and  undergoing  morphological  changes  while  the 
wall  is  thickening — the  different  layers  of  the  retina  are  formed.  It 
is  a  significant  fact  that  in  its  early  stage  this  wall  resembles  the 
brain  in  its  structure,  and  may  be  considered  as  a  part  of  that  organ. 
It  is  not  necessary  to  enter  into  a  more  detailed  description  of  the 
development  of  the  different  parts  of  the  eye. 

§  17.  The  ear  originally  appears  on  either  side  of  the  hind-brain 
as  an  involution  of  the  external  epiblast,  sunk  in  a  mass  of  the 
mesoblast.  It  is  then  simply  a  shallow  pit  with  a  wide-open 
mouth.  The  mouth  closes  up  and  the  pit  then  becomes  a  closed 
vesicle  (the  otic  vesicle)  which  is  lined  with  epiblast  and  sur- 
rounded by  mesoblast.  As  the  walls  of  this  vesicle  thicken,  its 
cavity  enlarges.  The  shape  of  the  vesicle  is  at  first  nearly  spheri- 
cal, but  it  soon  becomes  triangulai',  with  the  apes  of  the  triangle 
directed  inward  and  downward.  It  is  by  elongating  this  aj)ex  that 
the  rudiment  of  the  cochlear  canal  is  formed.  Part  of  the  vesicle 
becomes  stretched  into  a  long,  narrow,  hollow  process  (the  recess  us 
vestibidi),  and  from  the  outer  wall  of  the  main  body  two  pi-otube- 
rances  grow,  which  are  the  rudiments  of  the  vertical  semicircular 
canals.  These  parts  of  the  auditory  labyrinth  are  soon  more  clearly 
defined.  The  cochlear  canal  is  further  elongated  and  curved  ;  the 
recess  us  is  also  stretched  out  more  ;  and  from  a  new  protuberance 


212  EMBRYONIC   LIFE   OF   MAIT. 

tlie  horizontal  canal  is  developed.  Another  protuberance,  which 
becomes  apparent  at  the  inner  commencement  of  the  cochlear 
canal,  is  converted  into  the  sacculus  by  being  constricted  on  either 
side.  The  rest  of  the  cavity,  into  which  all  the  other  parts  open, 
may  now  be  called  the  utricidus.  Dilatations  of  the  semicircular 
canals  form  the  ampullae.  When  the  cochlear  canal  has  reached  two 
and  a  half  coils,  the  thickened  epithelium  of  its  lower  surface 
forms  a  double  ridge,  from  which  the  organ  of  Corti  is  developed. 
For  the  details  of  the  structure  of  the  labyrinth  we  refer  to  the 
previous  description  of  this  end-organ  of  sense. 

§  18.  All  the  coarser  differentiations  of  structure  to  which  refer- 
ence has  thus  far  been  made  are  only  the  expression — as  it  were — • 
of  certain  histogenetic  changes  which  have  been  secretly  taking 
place.  The  laj'ing  down  of  delicate  threads  of  nervous  tissue,  the 
proliferation  of  nerve-cells  along  definite  lines  of  movement,  have 
resulted  in  combining  these  elements  by  a  living  process  into  the 
organs  of  the  neiwous  mechanism.  The  white  matter  of  the  cord 
is  supposed  to  result  from  a  difierentiation  of  the  outer  parts  of  its 
superficial  cells  into  longitudinal  nerve-fibres  ;  the  latter  remain, 
however,  for  a  considerable  time  without  their  medullary  sheath. 
The  white  matter  first  appears  in  four  patches  at  the  front  and 
back  of  either  side,  in  which  the  individual  fibres  seem  like  smaU 
dots.  The  gray  matter  of  the  cord  is  formed  by  a  differentiation 
of  the  principal  mass  of  the  Avails  of  the  medullary  canal.  The 
outer  cells  first  lose  their  epithehal-like  arrangement,  and  then 
become  converted  into  true  nerve-cells,  with  prolongations  that 
constitute  nerve-fibres.  The  early  histological  character  of  the 
parts  of  the  brain  which  lie  back  of  the  cerebral  hemispheres  is 
very  similar  to  that  of  the  spinal  cord.  In  the  floor  of  the  hind- 
brain  and  mid-brain  a  superficial  layer  of  delicate  nerve-fibres  is 
early  formed.  The  cells  internal  to  the  nerve-fibres  give  rise  to 
the  epithelial  layer  which  lines  the  cavities  of  the  ventricles  and  to 
an  outer  layer  of  gray  matter.  In  the  fore-brain  the  walls  of  the 
hemispheres  become  divided  into  two  la3'ers,  between  which  the 
fibres  of  the  crura  cerebri  interpose  themselves.  The  inner  layer 
unites  with  these  fibres  to  give  rise  to  most  of  the  white  matter  of 
the  hemispheres  ;  the  outer  layer  of  rounded  cells  becomes  further 
differentiated  into  the  outer  part  of  the  gray  matter,  which  has 
comparatively  few  cells,  and  a  deeper  layer  with  numerous  cells, 
the  latter  forming  the  principal  mass  of  the  gray  matter  of  the 
cortex. 

§  19.  The  preceding  description  of  the  outlines  of  the  develop- 
ment of  the  human   nervous  mechanism  is  derived   for  the  mosi 


MECHAlSriCAL   THEORY    OF   THE   EMBRYO.  213 

part,  from  'the  study  of  other  embryos  than  those  of  the  human 
species.  It  is  probably,  however,  substantially  true  for  the  latter 
also.  It  is  valuable  for  the  purposes  of  Physiological  Psychology, 
chiefly  as  emphasizing  vphat  has  already  been  said  concerning  the 
structure  and  functions  of  this  mechanism  in  its  developed  form. 
The  nature  of  the  process  by  which  the  nervous  system  is  devel- 
oped, as  well  as  the  nature  of  the  developed  structure  and  its  func- 
tions, as  far  as  physical  science  can  go  at  all,  leads  us  in  the  direc- 
tion of  a  mechanical  theory.  But  in  respect  to  both,  such  a  theory 
is  at  present  in  an  exceedingly  fragmentary  and  uncertain  condition. 
Further  investigations  may  largely  remove  the  present  limitations. 
But  the  most  complete  theory  possible  can  hardly  be  more  than 
a  statement  of  the  order  and  extent  of  physical  changes,  the  real 
causes  and  meaning  of  which  it  lies  beyond  the  power  of  a  mechani- 
cal theory  to  give. 

The  impregnated  ovum  does,  indeed,  become  converted  into  the 
developed  organism  by  an  evolution  that,  at  every  step  in  its  course, 
appears  as  an  alteration  in  the  arrangement  of  material  molecules, 
under  conditions  derived  from  the  original  nature  of  the  molecules 
themselves,  from  their  necessary  relations  to  each  other,  and  from 
the  action  of  their  total  environment.  By  division  of  that  which 
was  single  into  several  parts,  by  bending  of  that  which  was  straight, 
by  stretching  in  one  direction  and  compressing  elsewhere,  by  swell- 
ing and  dilating  in  the  various  outlines  under  the  influence  of  press- 
ure, by  folding  and  tucking  in  so  as  to  close  up  an  opening  here 
and  form  another  there,  by  laying  down  cells  of  the  same  kind  in 
right  lines  or  grouping  them  in  masses,  etc. — in  brief,  by  motion 
of  pai'ticles  of  matter  in  such  way  that  the  motion  of  each  is  con- 
ditioned upon  that  of  the  others,  the  nervous  mechanism  is  built 
up.  What  it  can  accomplish  in  the  way  of  further  molecular  mo- 
tion, after  it  is  thus  built  up,  depends  of  course  in  large  measure 
"Upon  what  it  is  made  to  be  by  the  very  process  of  building.  Bow 
far  it  is  possible  even  to  propound  a  mechanical  theory  of  the  build- 
ing process  belongs  to  the  speculations  of  embryologists  to  con- 
sidei*.  It  is  our  next  problem  to  consider  as  a  whole  the  few  data 
upon  which  it  has  been  thought  possible  to  base  a  mechanical 
theory  of  the  behavior  of  the  nervous  system  after  it  has  once  beea 
constructed  as  a  result  of  the  embryonic  process. 


CHAPTER  YII. 
MECHANICAL  THEOEY  OF  THE  NEEVOUS  SYSTEM. 

§  1.  The  macliine-like  nature  of  much  of  tlie  structure  and  move- 
ment of  the  human  body  does  not  escape  the  most  ordinary  obser- 
vation. When  this  body,  either  as  a  whole  or  with  respect  to  some 
of  its  parts,  changes  its  position  in  space,  its  various  masses  sup- 
port and  act  upon  each  other  in  essentially  the  same  manner  as 
the  masses  of  matter  which  compose  the  parts  of  any  machine  con- 
structed by  human  skill.  Such  movement  is  possible  for  it,  because 
its  framework  of  boues  has  a  rigidity  sufficient  to  sustain  the  other 
less  rigid  organs  ;  and  because  the  bones  are  so  divided,  and  yet 
articulated,  that  they  can  assume  different  relations  toward  one  an- 
other in  accordance  with  the  simplest  principles  of  mechanics. 
The  laws  of  the  lever,  of  the  pulley,  the  ball-and-socket  joint,  etc., 
need  no  modification  when  applied  to  this  particular  machine  of  the 
human  body. 

The  action  of  certain  other  of  its  parts,  which  do  not  belong 
to  the  bony  framework  but  which  are  of  muscular  or  epithelial 
stnicture,  is  also  plainly  of  the  same  machine-like  character.  The 
movement  of  the  heart,  for  example,  is  in  part  to  be  explained  as 
that  of  a  pump  with  chambers  and  valves ;  and  the  flow  of  the 
blood  thi'oug-h  the  arteries  as  that  of  a  fluid  pumped  through  con- 
duits, of  unlike  and  changeable  sizes.  So,  too,  the  lungs  may  be, 
with  considerable  propriety,  compared  to  bellows  which  alternately 
suck  in  and  expel  the  surrounding  atmosphere.  The  optics  of  the 
eye  and  the  acoustics  of  the  ear  are  special  only  so  far  as  the  stnict- 
ure of  the  organs  makes  necessary  a  special  application  of  the  gen- 
eral laws  of  those  sciences.  Moreover,  the  distribution  of  the 
fluids  among  the  tissues  of  the  body  takes  place  under  the  laws 
which  govern  the  distribution  of  fluids  generally  when  separated  by 
membranes  which  they  can  permeate.  Nor  is  the  chemistry  of  the 
same  tissues  and  fluids  by  any  means  wholly  unlike  that  with  which 
the  experiments  of  the  laboratory  make  us  familiar.  When,  how- 
ever, we  begin  to  speak  of  those  changes  of  relative  position  which 
take  place  at  extremely  minute  distances  among  the  molecvdar  ele- 


MACHIJSrE   AND   MECHAIVTISM.  215 

ments  of  which  the  larger  masses  of  the  body  are  composed,  we 
seem  compelled  to  drop  the  conception  of  a  machine  and  to  seek 
both  another  conception  and  another  title. 

The  very  attempt,  then,  to  explain  the  motion  of  the  more  purely 
machine-like  parts  of  the  human  body,  leads  us  to  consider  certain 
activities  of  other  parts  for  which  the  word  "mechanism  "  is  more 
appropriate.  The  movement  of  none  of  the  more  or  less  rigid  or- 
gans of  the  body  originates  within  these  organs  themselves.  The 
changes  of  relative  position  in  the  parts,  with  which  the  ordinary 
laws  of  mechanics  deal,  imply  antecedent  molecular  changes  in 
other  parts  with  which  these  laws  cannot  deal.  The  motion  which 
finds  its  final  expression  in  the  swing  of  the  arm,  or  of  the  leg,  in 
the  lifting  of  a  weight,  and  even  in  the  contraction  of  the  heart,  or 
in  the  rising  and  falling  of  the  chest,  does  not  begin  in  arm,  or  leg, 
or  ribs,  or  diaphragm,  or  cardiac  muscles.  The  change  of  position 
of  so  considerable  masses  of  matter  is  but  the  summing-up  of  in- 
numerable minute  molecular  changes  which  began  within  the  body, 
but  outside  of  the  masses  themselves.  If,  for  example,  we  inquire 
as  to  what  causes  the  bones  to  move — however  strictly  their  mo- 
tion, once  begun,  may  follow  the  laws  of  mechanics — the  answer  is 
to  be  found  in  the  pull  of  the  tendons,  or  cord-like  structures, 
which  are  attached  to  them.  And  if  we  then  inquire,  What  causes 
the  tendons  to  pull  upon  the  bones  by  means  of  their  attachment  ? 
the  answer  must  be,  That  it  is  the  contraction  of  the  muscles  which 
pulls  upon  the  tendons. 

The  next  step  in  following  this  chain  of  causes,  however,  intro- 
duces us  to  a  different  class  of  considerations  from  any  of  the  fore- 
going. For  we  cannot  say  that  the  contraction  of  the  muscles  is 
caused  by  the  pull  of  the  nerves  upon  them.  The  movement  of 
muscular  fibre  in  contraction  is  an  altogether  dififerent  affair  from 
the  movement  of  the  bones  as  they  are  pulled  by  the  muscles  ;  nor 
do  the  nerves  act  upon  the  muscles  as  the  muscles  act  upon  the 
tendons.  The  elasticity  of  the  muscles  is,  indeed,  a  mechanical 
quality,  like  that  of  which  we  avail  ourselves  in  the  construction  of 
machines.  But  the  quality  of  elasticity  does  not  fully  explain  the 
behavior  of  the  so-called  muscle-nerve  machine  when  its  muscular 
tissue  is  contracting  or  relaxing.  Yet  the  Hving  muscle,  in  itself 
considered,  may  certainly  be  looked  upon  as  a  molecular  mechan- 
ism. It  is  a  system  of  minute  particles  of  matter  which  act  upon 
each  other  at  indefinitely  small  distances  ;  and  which,  when  any 
motion  is  set  up  at  one  part  of  it,  propagates  such  motion  accord- 
ing to  laws  that  are  given  in  the  very  constitution  and  arrangement 
of  the  particles  themselves.     This  is  precisely  what  we  understand 


216  THE   ISTEEVOUS   SYSTEM   A   MECilANISM. 

by  a  pbj-sical  molecular  mechanism.  The  office  of  the  nerve  with 
respect  to  the  muscle  is  simply,  as  we  know,  to  start  that  molecular 
activity  which  it  is  the  function  of  the  irritated  muscle  itself  to  ex- 
ercise. The  nerve,  however,  cannot  perform  its  office  of  irritating 
the  muscle  without  being  in  a  state  of  molecular  commotion  called 
the  "  excitement "  of  the  nerve.  And,  further,  this  excited  condition 
of  that  jDart  of  the  nerve  which  is  in  immediate  contact  with  the 
muscle  is  itself  a  state  of  the  nerve  which  has  been  propagated  from 
a  distant  point  of  the  nervous  matter.  All  the  machine-like  move- 
ments of  the  masses  of  the  body  require  us,  therefore,  to  look  for 
their  origin  in  minute  molecular  changes  that  originate  in  its  ner- 
vous elements.  And  for  the  further  account  of  these  neural  molec- 
ular changes  we  are  to  look  to  a  mechanical  theory  of  the  nervous 
s^'stem. 

§  2.  The  basis  for  a  general  view  of  the  nervous  system  as  a 
mechanism  has  been  laid  in  all  the  preceding  examination  ;  and 
it  cannot  be  denied  that  the  results  of  this  examination  are  such 
as  to  dispose  us  favorably  toward  the  attempt  to  develop  such  a 
view  into  a  complete  mechanical  theory.  Physical  science,  as  a 
matter  of  course,  strives  to  establish  such  a  theory.  It  knows  no 
other  way  of  considering  any  group  of  phenomena  when  brought 
before  it  for  examination.  To  deny  totally  the  application  of  the 
conception  of  a  mechanism  to  the  action  of  the  nervous  system 
would  be  to  refuse  to  apply  to  its  phenomena  the  same  scientific 
treatment  which  we  apply  to  all  other  physical  phenomena.  To 
limit,  a  priori,  such  application  would  be  to  restrict  improjperly,  on 
merely  theoretical  grounds,  the  area  of  the  phenomena  with  which 
such  science  is  entitled  to  deal.  The  fact  that  molecular  changes 
here  are  correlated  with  another  class  of  phenomena  which  we  call 
"  mental,"  in  no  wise  destroys  the  propriety  of  pushing  our  physical 
science  of  the  nervous  system  to  its  furthest  possible  limits.  The 
movements  of  all  material  bodies,  whether  in  the  elemental  shape 
of  the  molecules,  or  in  the  shape  of  the  same  molecules  when  aggre- 
gated into  masses,  as  well  as  the  laws  under  which  such  bodies  in 
movement  act  and  react  upon  each  other,  constitute  the  legitimate 
sphere  of  physical  science.  But  it  is  to  a  system  of  interacting 
molecules  that  the  conception  of  mechanism  especially  ajDplies. 
The  aim  of  physical  research  with  regard  to  any  given  system  of 
this  kind  is,  therefore,  not  accomplished  until  all  the  movements 
of  its  different  parts  are  explained  in  the  light  of  a  consistent 
mechanical  theory.  This  general  principle  of  all  physical  science 
neither  needs  nor  permits  a  special  exception  in  the  case  of  the 
human  nerves,  organs  of  sense,  and  brain. 


.      THE    CONSTITtTTIOlSr   MECHATSTICAL.  217 

On  the  other  hand,  the  very  unsatisfactoiy  condition  of  the  data 
for  a  mechanical  theory  of  the  human  nervous  system  has  been  im- 
plied in  each  of  the  preceding  chapters.  It  -will  appear  all  the 
more  plainly  now  as  we  present  briefly  a  statement  of  two  or  three 
such  theories  in  the  form  in  which  it  has  been  found  possible  for 
different  investigators  to  state  and  to  defend  them.  Nor  can  we 
express  much  confidence  that  physics  and  physiology  combined 
will  ever  be  able  to  point  to  a  complete  theory  of  so  intricate  and 
delicate  a  mechanism  as  this  nervous  system.  Moreover,  we  do  not 
by  any  means  affirm  that  a  purely  mechanical  treatment,  however 
complete,  would  of  itself  suffice  to  furnish  a  satisfactory  understand- 
ing of  all  the  phenomena  ;  or  even  that  the  phenomena  in  general 
could  by  any  possibility  be  brought  solely  under  the  terms  of  such 
treatment.  We  only  affirm  the  unrestricted  right  of  jDhysical  sci- 
ence to  attempt,  in  the  light  of  the  conception  of  mechanism,  an  ex- 
planation of  the  nervous  system  as  well  as  of  all  other  physical 
subjects  ;  and  also  its  right  to  its  ^Dersistent  faith  that — So  far  as 
■physical  science  can  explain  any  such  subject,  all  the  s^Decial  difficul- 
ties of  the  nervous  system  can  be  fitly  considered  only  in  this  way. 

§  3.  The  chemical  constitution  and  structural  form  of  the  ele- 
ments of  nervous  matter  require  that  the  system  which  they  com- 
pose should  be  regarded  in  the  light  of  the  concej)tiou  of  mechan- 
ism. It  is  true  that  physical  science  cannot  give  an  accurate  descrip- 
tion of  the  chemical  processes  which  take  place  in  the  formation  of 
the  nerve-fibres  and  nerve-cells,  or  during  their  functional  activity  ; 
it  cannot  do  so  much  as  this  for  the  living  tissues  generally.  But 
it  finds  here  the  same  chemical  elements  which  exist  elsewhere 
in  nature,  esj)ecially  the  four  elements,  oxygen,  hydrogen,  nitrogen, 
and  carbon.  It  nowhere  finds  these  elements  behaving  differently 
in  the  nervous  system  from  the  way  in  which  it  is  their  nature  to 
behave  elsewhere,  under  similar  circumstances.  And  the  fact  that 
precisely  similar  circumstances  do  not  occur  to  induce  the  same 
combination  and  interaction  of  these  elements  outside  of  the  ner- 
vous sj'stem,  is  traced  back  to  its  causes  in  a  succession  of  occur- 
rences that  all  have  the  character  belonging  to  the  chemistry  of 
living  tissues.  We  know  of  no  sap  which  is  suitable  for  forming- 
organisms  in  general,  but  which  is  itself  a  perfectly  homogeneous 
fluid.  Nucleated  granules  in  the  very  chemical  constituents  which 
give  conditions  to  all  the  subsequent  activity  of  the  molecules,  are 
revealed  by  microscopic  examination  of  those  cells  from  which  the 
whole  body  springs.  This  fact,  together  with  the  character  of  the 
subsequent  process,  may  lead  some  to  insist  that  a  certain  special 
form   of  energy  (called  "vital  force,"  or  by  some  less  obnoxious 


218  THE   NERVOUS   SYSTEM   A   MECHANISM. 

title),  is  marslialling  the  minute  particles  under  its  superior  control 
But  such  way  of  considering  the  phenomena — whether  admissible 
or  inadmissible — does  not  at  all  help  us  to  dispense  with  the  purely 
mechanical  point  of  view.  In  the  original  living  germ  with  which 
the  organism  began,  and  in  all  its  subsequent  development,  every 
chemical  change  in  nervous  matter  is  nothing  more  than  a  move- 
ment of  physical  molecules,  strictly  under  the  conditions  furnished 
by  their  constitution  and  previous  arrangement. 

The  general  significance  of  the  chemical  constitution  of  ner- 
vous matter,  with  reference  to  a  mechanical  theory  of  the  nervous 
system,  is  by  no  means  wholly  obscure.  It  is  obvious  that  all  the 
energy  expended  in  the  movement  of  the  body  as  a  whole,  or  of  its 
larger  masses,  originates  in  minute  molecular  changes.  The  latter 
changes  have,  of  course,  a  direct  relation  to  the  chemical  constitu- 
tion of  the  tissues  in  which  they  occur.  The  muscular  fibre  can 
contract  because  its  molecules  admit  of  that  rearrangement  in 
which  the  contraction  essentially  consists  ;  for  doing  the  amount  of 
work  implied  in  such  rearrangement,  this  fibre  is,  of  course,  depen- 
dent upon  its  own  chemical  constitution.  But  the  source  of  the 
excitation  of  the  muscle  is  to  be  found  in  antecedent  molecular 
changes  within  the  nervous  system  ;  indeed,  all  the  changes  that 
are  to  be  summed  up  in  the  work  done  by  and  within  the  rigid 
masses  of  the  body  have  their  origin  here.  It  accords,  then,  with 
the  mechanical  conception  of  the  nervous  system  that  its  chemistry 
should  be  just  such  as  we  have  seen  that  it  actually  is.  Nervous 
matter  holds  in  store  a  large  amount  of  energy  that  is  easily  dis- 
posable ;  of  energy  that  will  be  yielded  freely  and  rapidly  if  any- 
thing occurs  to  start  the  process  within  the  system  of  molecules 
of  which  such  matter  is  composed.  For  the  molecules  are  of  such 
kind  as  readily  break  up  and  recombine  their  elements  in  simpler 
forms  ;  in  doing  this  they  render  kinetic  a  large  amount  of  energy 
which  they  have  previously  held  latent. 

No  mechanical  theory  of  the  nervous  system  can  explain  the 
meaning  of  all  the  various  structural  forms  which  the  elements  of 
this  system  assume.  It  cannot  be  told,  for  example,  what  pecuUar 
place  in  the  mechanism  belongs  to  the  different  shapes  of  nerve- 
cells,  bipolar,  multipolar,  stellate,  etc.  Nor  can  a  complete  picture 
be  drawn  of  the  dift'erences  in  character  which  the  nerve-commotion 
takes  as  it  passes  from  the  nerve-fibres  to  the  nerve-cells,  or  from 
one  nerve-cell  to  another.  We  can  only  insist  upon  the  undoubted 
general  fact  that  all  these  structural  forms  have  whatever  signifi- 
cance belongs  to  them,  because  they  are  themselves  molecular 
structures,  capable  of  undergoing,  in  relation  to  each  other,  those 


,    THE    AERANGEMENT   MECHANICAL.  219 

very  changes  in  which  the  functional  activity  of  the  nervous  system 
consists. 

§  4.  There  can  be  no  doubt  that  the  arrangement  of  the  nervous 
elements  into  a  system  corresponds  to  the  conception  of  mechanism. 
A  certain  work  of  "concatenating"  the  different  physical  systems  of 
the  body,  and  of  adjusting  its  relations  to  the  changes  in  its 
environment,  requires  to  be  accomplished.  This  problem  demands 
a  three-fold  exercise  of  function  ;  it  is  a  problem  in  the  construction 
of  a  mechanism.  The  nervous  system  actually  is  of  threefold  con- 
struction ;  its  threefold  construction  is  the  answer  which  it  prac- 
tically makes  to  the  above-mentioned  problem.  One  part  of  the 
complex  problem  consists  in  the  conversion  of  certain  of  those 
molecular  motions  which  take  place  in  nature  outside  of  the  living- 
organism  into  molecular  motion  within  the  tissues  of  such  organism. 
The  solution  of  this  part  of  the  problem  is  furnished  by  the  end- 
organs  of  the  nervous  system.  The  end-organs  are  those  special 
mechanisms  which  are  adaj)ted  to  convert  the  molecular  motions 
called  stimuli  into  the  molecular  motions  called  neural  excitation. 
That  by  far  the  larger  portion  of  the  eye  and  ear,  for  example,  acts 
in  a  purely  mechanical  way,  there  is  no  doubt.  It  is  the  office  of 
the  great  mass  of  the  eye  to  transmit  and  refract  the  rays  of  light ; 
of  the  ear  to  transmit  and  condense  the  acoustic  waves.  But  when 
the  nervous  elements  of  the  retina  and  of  the  organ  of  Corti  re- 
ceive the  physical  processes  transmitted  to  them,  they  transmute 
these  physical  processes  into  physiological  neural  processes  ;  in 
doing  this  they  act  as  special  molecular  mechanisms. 

The  second  j)art  of  the  complex  problem  before  the  nervous  sys- 
tem consists  iu  the  conduction  in  all  necessary  directions  of  these 
neural  processes  ;  only  on  this  condition  can  distant  parts  of  the 
nervous  system  act,  as  it  were,  in  view  of  each  other,  and  thus  the 
whole  body  be  bound  into  a  living  unity  under  the  influence  of 
changes  in  its  environment,  and  iu  the  ideas  and  impulses  of  the 
mind.  The  nerve-fibres  solve  this  part  of  the  problem.  This  they 
do  by  acting  as  mechanisms,  which  have  such  a  molecular  constitu- 
tion and  function  that  a  commotion,  started  at  any  point  in  tbe 
physical  elements  of  the  system,  spreads  from  molecule  to  molecule, 
in  accordance  with  the  laws  of  the  system. 

The  third  part  of  the  same  complex  problem  requires  for  its  solu- 
tion structures  and  functions  still  more  intricate  and  inexplicable. 
Incoming  molecular  disturbances  must  be  modified  and  redistributed 
so  as  to  give  rise  to  outgoing  molecular  disturbances  along  definite 
tracts,  in  order  that  definite  groups  of  muscles  may  be  made  to  con- 
tract.    Only  in  this  way  can  the  whole  physical  organism,  by  a  so- 


220  THE   NERVOUS    SYSTEM    A   MECHANISM. 

called  reflex  activity,  adjast  its  condition,  in  view  of  the  presence  of 
given  kinds  and  degrees  of  stimuli.  Moreover,  the  vital  functions — 
the  movements  that  control  respiration,  digestion,  circulation  of  the 
blood  and  of  other  fluids,  etc. — must  be  united  so  as  to  work  to  a 
common  end,  and  with  the  modified  forms  and  degrees  of  their  re- 
spective energies,  which  the  changing  circumstances  require.  Still 
further,  not  only  must  the  neural  processes  set  up  by  the  end-or- 
gans and  conducted  inward  by  the  afferent  nerves  have  a  place  of 
meeting  in  j)i'oximity  with  the  centres  of  origin  for  the  correspond- 
ing efferent  impulses  ;  but  all  the  neural  processes  in  this  place  of 
meeting  must  also  be  so  modified  and  made  mutually  dependent 
that  they  can  be  correlated,  under  psycho-physical  laws,  with  the 
processes  of  mind.  It  is  the  central  organs  which  alone  possess 
the  molecular  construction  and  functions  necessary  for  such  won- 
derful reflex  and  automatic  activities.  In  their  highest  form — the 
hemispheres  of  the  human  brain — they  solve  the  problem  of  pro- 
viding a  system  of  molecules,  whose  constitution  and  changes  may 
be  immediately  related  with  the  phenomena  of  mind.  These  central 
organs  are  extremely  intricate  physical  structures.  It  cannot  be 
pretended  that  even  a  beginning  has  been  made  toward  a  satisfac- 
tory theory  of  their  functional  activity  considered  as  a  special  case 
in  molecular  physics.  But  this  fact  does  not  affect  the  confidence 
which  is  based  upon  what  is  known  of  physical  structures  in  gen- 
eral, that  in  these  organs,  the  changes  wliich  take  place  are  essen- 
tially of  the  same  order  as  are  those  with  which  the  science  of  mo- 
lecular physics  has  elsewhere  to  deal.  They  are  modes  of  motion  in 
which  the  behavior  of  each  molecule,  regarded  as  a  constituent 
element  of  the  system,  is  conditioned  upon  the  constitution  and 
behavior  of  the  other  members  of  the  same  system.  That  is  to 
say,  the  central  organs  must  be  regarded  in  the  light  of  the  con- 
ception of  mechanism. 

§  5.  The  general  office  of  the  nervous  system  may,  then,  be  de- 
scribed in  somewhat  the  following  manner.  The  development  of  a 
rich  and  varied  life,  both  animal  and  intellectual,  requires  a  great 
store  of  sensations  and  of  motions.  Tlie  sensations  are  jDrimarily 
designed  to  serve  as  signs  of  changes  in  the  environment  of  the 
animal  to  \^hich  his  condition  must  be  adapted  by  movement  of 
his  l)odily  parts  ;  but  they  are  also  to  serve  as  a  basis  for  intel- 
lectual attainment  and  development.  The  forces  of  external  nature 
continually  storm  the  peripheral  parts  of  the  animal's  body.  In 
order  that  any  of  these  forces  may  act  as  the  stimuli  of  sensations, 
they  must  be  converted  into  molecular  motions  within  the  tissues 
of  this  body.     In  order,  further,  that  the  masses  of  the  body  may 


.     THE   EQUILIBKATING   MECHAlSriCAL.  221 

constantly  be  readjusted  to  tlie  external  changes  of  which  the  sen- 
sations are  signs,  the  molecular  motions  must,  in  turn,  be  converted 
into  movements  of  these  masses.  In  other  words,  a  process  of  con- 
stant interchange  must  take  j)lace  between  the  animal  organism 
and  external  nature. 

Disturbances  in  one  part  of  the  body,  by  the  play  upon  it  of  nat- 
ure's energ}',  instead  of  becoming  injurious  or  destructive,  are 
thus  made  serviceable  through  inducing  the  needed  disturbances 
of  other  j^arts  of  the  same  body.  The  equilibrium  on  which  life 
depends  is  maintained.  Moreover,  the  material  necessary  for  self- 
conscious  development,  for  a  growing  knowledge  of  the  so-called 
outside  world,  is  furnished  through  the  conduction  of  these  dis- 
turbances to  their  common  meeting-places  iii  the  central  organs. 

To  accomplish  the  general  work  of  equilibrating  the  interaction 
of  the  different  jjarts  of  the  body,  of  readjusting  its  condition  to 
the  changing  condition  of  its  surroundings,  some  special  construc- 
tion and  arrangement  of  material  molecules  is  necessary.  If  the 
work  is  to  be  done  in  a  highly  elaborate  way,  a  very  intricate  ar- 
rangement of  an  indefinitely  great  number  of  chemically  complex 
molecules  is  necessary.  Such  an  an-angement  is  the  human  ner- 
vous system.  But  just  because  its  arrangement  and  function  are 
of  this  kind,  it  is  a  "  mechanism."  As  a  highly  complex  molecular 
mechanism  it  utilizes  the  disturbances  which  arise  from  the  en- 
vironment. It  binds  together  all  the  other  systems  of  the  body  in 
living  reciprocity  of  energies  and.  functions.  Its  superficial  parts 
are  so  constructed  that  they  can  be  set  in  motion  by  various  forms 
of  physical  energy — by  light,  heat,  sound,  chemical  change,  etc.  ; 
they  are  also  adapted,  fitly  to  modify  the  impressions  thus  received. 
The  molecules  of  its  conducting  nerves  are  so  constituted  and  ar- 
ranged that  they  can  indicate  the  path  along  which  the  disturbance 
thus  occasioned  must  pass ;  they  can  dictate  the  conditions  and 
laws  under  which  its  course  must  be  completed.  The  molecules  of 
its  central  organs  are  capable  of  assuming  inconceivably  varied  re- 
lations to  each  other,  of  thus  transmuting  and  redistributing  the 
nerve-commotions  which  reach  them  along  the  incoming  tracts,  and 
even  (it  would  seem)  of  starting  automatically  outgoing  disturb- 
ances in  response  to  self-conscious  sensations  and  ideas. 

But  all  the  foregoing  offices  of  the  nervous  system  are  nothing 
but  the  jnovements  of  physical  elements,  in  constant  reciprocal  de- 
pendence upon  each  other,  though  in  response  to  excitations  lying 
outside  of  the  system  itself.  To  move  thus  is  the  function  of  a 
molecular  mechanism.  So  far  as  science  can  control  the  different 
parts  of  the  nervous   system  for  experimental  purposes,  it  finds 


222  THE   NERVOUS   SYSTEM   A   MECHANISM. 

them  behaving  in  such  a  manner  as  to  make  a  plain  demand  for  a 
physical  and  mechanical  theory  in  explanation  of  their  behavior. 

§  6.  The  foregoing  description  of  the  nervous  system  as  a  mech- 
anism, like  all  similar  descriptions,  undoubtedly  lacks  scientific 
quality.  It  is  neither  exact  nor  in  such  form  as  to  admit  of  ex- 
l^erimental  verification.  It  is  largely  based  upon  conjectures,  full 
of  gaps  and  assumptions  ;  and  were  it  pressed  at  every  point  for 
proof,  it  would  be  obliged  to  rely  much  upon  general  principles  in 
mechanics  (the  special  applications  of  which  to  the  case  in  hand  are 
by  no  means  certain  or  obvious),  and  even  to  indulge  in  hopes  and 
promises  with  reference  to  the  future,  rather  than  present  demon- 
stration. May  we  not  know  more  precisely  the  nature  of  the  mo- 
lecular changes  which  constitute  the  functions  of  nerve-fibres  and 
nerve-cells  ?  Cannot  physical  science  help  us  to  complete  these  be- 
ginnings of  a  theory  ? 

In  answer  to  the  question  just  raised  we  have  already  seen  how 
little  satisfaction  is  afforded  on  applying  to  the  science  of  chemistry. 
On  general  principles  of  physical  science  there  can  be  little  doubt 
that  the  excitation  and  conduction  of  nerve-commotion  is  dependent 
upon  a  chemical  change  in  the  nervous  tissue  itself.  Moreover,  we 
know  that  the  j)rocess  of  conduction  in  the  nerve  requires  each  of 
its  molecules  to  act  upon  the  neighboring  elements  as  the  condition 
of  the  process  continuing.  Nor  can  this  process  itself  be  a  mere 
impartation  of  motion,  from  molecule  to  molecule  ;  on  the  contrary, 
the  phenomena  of  electrotonus  seem  to  show  that  it  must  also  con- 
sist in  the  setting  free  of  energy  which  exists  latent  within  the 
molecules  of  the  nerve-substance.  These  molecules  contain,  then, 
by  virtue  of  their  constitution,  stored  or  potential  energy  which  is 
converted  into  kinetic  energy  in  the  propagation  of  the  process  of 
excitation,  and  which  is  expended,  in  part,  in  either  inhibiting  or 
increasing  the  energy  of  that  process.  Such  potential  energy  can 
scarcely  be  other  than  chemical. 

Accordingly,  we  should  be  tempted  to  describe  the  process  of 
progressive  excitation  of  the  nerve  somewhat  as  follows  :  Every 
element  of  the  nerve,  by  reason  of  its  highly  complex  and  unstable 
chemical  constitution,  contains  a  large  store  of  energy  ;  the  excite- 
ment of  the  nerve  consists  in  the  explosive  decomposition  succes- 
sively of  these  elements  of  the  nerve  ;  and  the  result  of  the  decom- 
position is  the  setting  free  of  the  stored  energy  to  be  expended  in 
part  in  the  excitation  of  the  next  adjoining  elements.  The  process, 
then,  is  not  altogether  unlike  the  burning  of  a  line  of  powder 
grains.  Such  an  hypothesis,  however,  would  at  once  have  to  answer 
several  difficult  questions.    "Why  does  not  the  whole  of  the  exjilosive 


INTERFERENCES   OF   NERVE-COMMOTION.  223 

substance  burn  up,  instead  of  only  an  amount  of  it  approximately 
proportional  to  the  strength  of  the  stimulus  which  sets  the  process 
ao-oing  ?  Analogies  may  indeed  be  found  in  the  union  of  chlorine 
and  hydrogen  under  the  action  of  light.  What  checks  the  process 
in  the  nerve  as  a  whole,  and  what  limits  it  quantitatively  in  a  differ- 
ent way  at  different  points  in  its  course,  so  as  to  give  the  phenomena 
of  anelectrotonus  and  catelectrotonus  ?  (comp.,  Chap.  III.,  §  19  f.). 
Moreover,  direct  observation  has  as  yet  discovered  no  indisputable 
evidence  of  functional  chemical  changes  in  the  nerve-fibres.  If 
such  changes  exist  at  all  they  are  exceedingly  small. 

§  7.  Allusion  has  been  made  (p.  119  f.)  to  the  fact  that  the  effect 
of  several  excitations  of  a  nerve-stretch  is  compounded,  as  it  were, 
in  the  action  of  the  attached  muscle.  That  is  to  say,  excitations 
which  are  simultaneous,  or  which  follow  each  other  with  sufficient 
and  not  too  great  rapidity,  are  summed  up  in  the  nerve,  like  mo- 
lecular waves  of  nerve-commotion  piled  upon  each  other.  Besides 
such  phenomena  of  "  summation,"  there  exist  analagous  phe- 
nomena of  so-called  "  interference  ;  "  and,  further,  of  the  facilitat- 
ing effect  which  one  excitation  has  upon  others  following  it  along 
the  same  paths  of  conduction,  especially  in  the  central  organs. 
These  and  similar  phenomena  tempt  us  to  consider  the  activity  of 
the  nervous  substance  in  terms  of  an  exceedingly  complex  sum  in 
the  addition  and  subtraction  of  molecular  disturbances  of  a  wave- 
like character.  Elaborate  experiments  have  been  made  to  deter- 
mine the  laws  under  which  such  summation  or  interference  of 
electrical  excitations  takes  place.  Thus  G.  Valentin'  assumes  that 
the  case  of  the  nerves  comes  under  the  general  theory  of  molecular 
waves  that  may  either  be  piled  upon  each  other,  or  may  interfere 
with  each  other.  The  interferences  he  calls  "  positive  "  when  the 
currents  are  moving  in  the  same  direction,  "  negative  "  when  they 
are  moving  in  opposite  directions  ;  and  such  currents  may,  of 
course,  be  either  ascending  or  descending.  The  character  of  the 
interferences  is  to  be  defined  by  the  way  in  which  the  nerve-muscle 
machine  responds  to  these  four  kinds  of  interference.  The  inter- 
ference has  a  heightening  effect  (is  erhohende)  when  the  result 
indicated  by  the  behavior  of  the  muscle  is  greater  than  the  sum  of 
two  single  effects  from  the  partial  excitations  that  are  compounded  ; 
a  depressing  effect  when  the  result  is  less  than  this  sum.  If  the 
effect  of  the  interference  is  such  as  to  reduce  the  result  to  zero, 
it  is  called  inhibitory.  Valentin  concludes  that,  in  case  of  inter- 
ferences of  excitations  from  one  and  the  same  current  (with  respect 

'  In   PfliJger  s   Archiv,    vii.    (1873),   pp.   458-496,  article   on  the  Interfer- 
ences of  Electrical  Excitations. 


224  THE  NERVOUS   SYSTEM   A   MECHAISTISM. 

to  degree,  direction,  etc.),  the  character  of  the  effects  produced 
depends  upon  the  original  molecular  constitution  of  the  nerve. 
Just  as  its  constitution  is  decisive  with  regard  to  the  nature  of  the 
muscular  contractions  that  follow  a  single  excitation  of  the  nerve, 
so  is  it  also  decisive  with  regard  to  the  results  of  interference. 
These  results,  moreover,  conform  to  the  same  laws  after  decapita- 
tion or  poisoning  as  before.  And  further,  the  same  rules  govern 
in  the  case  of  interferences  of  two  currents,  if  both  the  currents 
are  of  about  the  same  degree  of  strength.  Finally,  according  to 
Valentin,  the  same  rules  belong  to  the  interferences  that  occur  in 
cases  of  reflex  action,  or  of  the  stimulation  of  motor  nerves  through 
the  sensory,  as  those  which  apply  to  the  direct  stimulation  of  the 
motor  nerves.  It  is  apparent  that  the  only  net  gain  from  the  fore- 
going experiments  consists  in  the  information  that  the  molecular 
constitution  of  the  nerves  themselves  determines  all  the  variable 
elements  in  the  results  of  exciting  them.  But  this  would  be  an 
assumption  fairly  made  by  every  attempt  at  a  physical  science  of  the 
nervous  functions.  And  inasmuch  as  we  can  make  no  such  veri- 
fiable statements  concerning  the  nature  of  this  molecular  constitu- 
tion as  will  serve  the  purposes  of  a  precise  mechanical  theory,  it  is 
hard  to  see  what  advance  has  been  gained  toward  the  construction 
of  such  a  theory. 

The  jDhenomena  caused  by  the  reciprocal  action  of  different  ex- 
citations within  the  central  nervous  system  are,  of  course,  much 
more  complex  and  difficult  to  bring  under  a  theory  of  molecular 
wave-like  impulses,  than  are  the  phenomena  of  the  comparatively 
simple  nerve-muscle  machine.  A  fortiori,  molecular  physics  is 
unable  to  propose  a  satisfactory  theory  for  the  central  organs. 
According  to,  Exner,'  many  of  the  phenomena  are  covered  by  the 
general  principle  that  one  excitation  acts  io  facilitate  or,  as  it  were, 
smooth  the  path  for  others  passing,  after  only  a  brief  interval,  along 
the  same  course.  This  principle  he  distinguishes  from  that  of 
''summation,"  when  applied  to  reflex  action.  The  latter  term  Exner 
applies  to  the  accumulation  in  the  central  organ  of  excitations 
which,  taken  singly,  are  too  weak  to  produce  any  reflex  motion,  but 
which  by  their  combined  strength  do  produce  such  motion.  The 
principle  of  "facilitation,"  however,  refers  to  the  condition  of  the 
central  parts  after  the  passage  through  them  of  a  stimulus  which 
has  already  called  forth  some  reflex  action.  Exner's  experiments 
led  him  to  conclude  that  the  motor  excitation  of  some  one  ex- 
tremity from  the  brain  (that  is,  by  stimulating,  in  the  brain,  the 
so-called  motor  area  of  the  extremity)  facilitates  the  subsequent  pas- 
'  Article  in  PflLiger's  ArcLiv.,  xxviii.,  pp.  487  ff. 


'PHYSICS   OF   THE   CENTRAL   ORGANS.  225 

sage  of  reflex  stimulus  affecting  the  same  extremity  ;  and,  con- 
versely, stimulating  an  extremity  reflexly  facilitates  the  passage  of 
a  subsequent  motor  excitation  from  the  area  of  the  bi'ain  to  the 
same  extremity.  Thus,  for  example,  the  reflex  motions  of  the  fore- 
leg of  a  rabbit,  produced  by  stimulating  the  toes  of  that  leg,  were 
found  to  be  increased  in  intensity  if  the  so-called  cerebral  motor 
centre  of  the  fore-leg  was  also  stimulated.  Different  reflex  excita- 
tions also  may  facilitate  each  other's  effect  in  the  same  way.  For 
example,  the  sensory  stimulation  of  the  left  foot  has  the  effect  of 
facilitating  the  reflex  act  which,  as  it  might  appear,  would  relate 
only  to  the  right  foot  and  its  motor  area  in  the  central  organ  ;  and 
such  reflex  action  of  the  right  foot  facilitates  the  contraction  set 
fz'ee  in  the  same  foot  by  stimulating  the  left-foot  section  of  the  spi- 
nal cord.  Exner  was  unable,  however,  to  obtain  any  inhibitory 
effect  upon  the  motion  of  the  extremities  by  stimulating  various 
other  places  of  the  cortex  of  the  cerebrum,  or  by  stimulating  the 
cerebellum.  He  also  found  that  when  one  side  of  the  cortex  of  the 
cerebrum  is  stimulated  by  electricity  so  as  to  produce  a  condition 
of  tetanus  in  one  extremity  of  the  animal,  the  results  of  two  excita- 
tions— one  as  a  reflex  from  the  foot  and  one  directly  from  the  same 
side  of  the  brain — are  compounded  in  a  way  which  seems  incom- 
patible with  any  known  form  of  the  summation  and  interference 
of  molecular  wave-like  disturbances. 

Indeed  (to  return  to  the  simpler  case),  Griitzner  '  seems  justified 
in  saying  that,  strictly  speaking,  we  cannot  without  qualification 
even  represent  what  takes  place  when  two  currents  of  electricity 
act  in  combination  upon  a  nerve,  as  though  it  were  a  matter  of  the 
addition  or  subti'action  of  their  separate  effects.  For  it  is  possible 
that  an  electrical  current  of  an  intensity  equal  to  the  d,mount  of  the 
natural  nerve-current  (current  of  rest  =  a)  and  the  current  used  as 
stimulus  (current  of  action  =  b),  taken  together  (a  +  b),  will  not  ex- 
cite a  nerve  that  shows  no  current  at  all,  although  the  latter  (b) 
alone  will  excite  the  nerve  if  just  previously  the  former  {a)  was 
present  in  the  nerve.  The  currents  already  existing  in  the  nerve, 
when  the  exciting  current  is  applied,  are,  therefore,  not  simply 
added  to  or  subtracted  from  the  latter  ;  but  they  produce  molecu- 
lar changes  of  an  unknown  kind  which  tend  to  induce  the  origina- 
tion of  so-called  "  cathodic  "  and  "anodic"  places  in  the  nerve — 
that  is,  places  of  exalted  and  places  of  depressed  excitability. 
Thus  a  weaker  current  will  excite  the  nerve  when  it  is  in  a  condi- 
tion of  exalted  excitability  ,  a  stronger  current  may  fail  to  excite 
the  nerve  when  in  a  condition  of  depressed  excitability. 

'  See  Pfliiger's  Arcliiv,  xsviii.,  p.  144  f. 
15 


226  THE   ELECTRICAL   THEORIES. 

How  obscure  and  complicated  are  the  molecular  conditions  con- 
nected with  the  excitation  of  the  nerve  is  further  shown  by  the 
effect  of  giving  different  treatments  to  the  cross-section  of  the  nerve. 
If  the  nerve  is  simply  cut,  its  behavior  under  stimulation  is  differ- 
ent from  that  which  occurs  when  it  has  been  bound  before  the 
cross-section  is  made.  Binding  the  nerve  produces,  for  some  min- 
utes after  cross-section,  a  large  increase  of  its  excitability  in  the 
immediate  neighborhood  of  the  injui-ed  place  ;  this  is  true  for  all 
kinds  of  stimuli,  including  the  electric  current  in  both  directions. 
From  five  to  ten  minutes  subsequently,  however,  the  making  of  the 
current  in  the  opposite  direction  to  the  current  induced  by  cross- 
section  has  frequently  a  diminished  rather  than  an  increased  effect. 

§  8.  On  the  whole,  it  would  appear,  then,  that  the  ability  to  lay 
even  a  basis  for  a  strictly  scientific  molecular  theory  of  the  nervous 
mechanism  depends  upon  the  ability  satisfactorily  to  explain  the 
electrical  process  in  the  nerves  and  their  consequent  behavior  under 
electrical  stimulation.  It  would  by  no  means  follow  that  a  com- 
plete theory  for  the  comparatively  simple  phenomena  of  the  nerve- 
muscle  machine  would  furnish  the  sure  clew,  not  to  say  the  full 
explanation,  of  all  the  activities  of  the  nervous  system.  On  the 
contrary,  the  evidence  is  overwhelming  that  the  working  of  the 
complete  nervous  mechanism  involves  other  principles  than  those 
which  may  be  deemed  sufficient  for  the  case  of  the  single  nerve 
and  muscle  when  under  electrical  stimulation.  But,  plainly,  the 
more  complex  case  cannot  be  solved  without  fii'st  solving  the  far 
less  complex  one.  And  yet  the  simplest  possible  case  of  nervous 
molecular  mechanism — the  case  that  can  be  brought  under  the 
most  favorable  experimental  conditions — has  thus  far  proved  to 
lie  beyond  oui"  power  to  find  a  satisfactory  scientific  solution. 

The  two  most  important  principles  which  must  enter  into  any 
mechanical  theory  for  explaining  the  behavior  of  nerves  in  relation 
to  electricity  are,  according  to  Hermann  :  '  (1)  the  law  of  electrical 
excitation,  and  (2)  the  law  of  the  so-called  current  of  action.  The 
phenomena  upon  which  these  laws  are  themselves  based  are  chiefly 
the  phenomena  of  electrotonus  and  the  phenomena  of  negative 
variation. 

It  is  a  fact  (see  p.  114  f.)  that  the  passage  of  the  electrical  current 
through  a  nerve-stretch  produces  in  the  nerve  a  changed  condi- 
tion of  excitabilit}^  called  electrotonic.  This  condition  is,  however, 
different  for  different  parts  of  the  nerve-stretch.  It  is  dependent 
upon  the  nearness  of  each  part  to  the  electrodes,  it  being  greatest 
in  their  vicinity.  It  is  dependent  on  the  strength  of  the  polarizing 
'  Handb.  d.  Physiol.,  II.,  i.,  p.  193. 


TIIEOJJY    OF   DU   BOIS-EEYMOND.  227 

current  and  on  the  length  of  the  stretch  through  which  it  flows. 
Its  intensity  is  greater  on  the  side  of  the  anode  than  on  the  side 
of  the  cathode.  The  condition  may  be  said  to  be  one  of  increased 
excitabihty  in  the  region  of  the  cathode,  of  diminished  excitabihty 
in  the  region  of  the  anode.  Helmholtz  found  that  the  time  of  the 
development  of  the  electrotonic  condition  is  not  perceptibly  later 
than  that  of  the  electrical  current  which  excites  it ;  the  condition 
originates  at  the  moment  of  making,  and  ceases  at  the  moment  of 
breaking,  the  polarizing  current.  Du  Bois-Reymond  concludes, 
thereupon,  that  the  electrotonic  condition  is  spread  over  the  nerve 
with  a  speed  equal  to  that  of  the  process  of  excitation. 

It  is  also  a  fact  (see  p.  117  f.)  that,  in  the  case  of  the  nerve-stretch 
as  well  as  in  that  of  the  muscle,  the  galvanometer  shows  the  pas- 
sage of  a  current  when  one  of  the  electrodes  is  placed  at  its  cut 
end  and  the  other  at  its  equator.  It  is  a  fact  that  this  so-called 
natural  current,  or  current  of  rest,  is  diminished  by  the  stimula- 
tion of  the  nerve  with  an  interrupted  current,  or  by  other  means 
of  exciting  it — the  diminution  being  shown  by  the  return  of  the 
needle  of  the  galvanometer  toward  the  zero-point  (the  so-called 
"  vegative  variation  "). 

§  9.  The  two  principal  theories  which  have  hitherto  attempted 
to  account  for  the  above-mentioned  facts  are  the  theoi'ies  of  du 
Bois-Reymond  and  of  Hermann.  Du  Bois-Reymond '  assumes 
that  in  the  substance  of  the  nerve  there  exists  an  arrangement  of 
electro-motive  molecules  embedded  in  an  imperfectly  conducting 
medium.  Each  molecule  is  like  a  minute  battery  with  positive  and 
negative  poles  ;  and  the  molecules  present  their  positive  surfaces  to 
the  longitudinal  surface  of  the  nerve,  their  negative  surfaces  to  the 
cut  ends  or  transverse  sections  of  the  nerve.  The  presence  of  these 
molecules  gives  rise  to  currents  in  the  medium  which  surrounds 
them.  Owing  to  the  imperfect  conductivity  of  the  medium,  such 
currents  flow  in  more  or  less  concentric  lines  at  some  distance 
from  each  molecule.  The  current  which  exists  in  the  nerves 
(exists,  according  to  du  Bois-Reymond,  as  natural  to  the  nerve  and 
previous  to  its  injury  by  cross-section),  and  which  is  made  obvious 
by  the  deflection  of  the  needle  of  the  attached  galvanometer,  may 
therefore  be  regarded  as  the  resultant  of  the  numerous  unobserv- 
able  currents  belonging  to  the  several  molecules.  In  this  way  the 
so-called  "  cui'rent  of  rest "  is  to  be  explained.  Du  Bois-Reymond 
is  forced  to  account  for  the  fact  that  such  natural  currents  are 

'  The  views  of  du  Bois-Reymond  are  to  be  fouud  in  his  Untersuchungen 
liber  thierische  Electricitat,  1848-49,  and  Gesammelte  Abhaudluugen,  etc., 

1875-77. 


THE   ELECTRICAL   THEORIES. 

either  exceedingly  small  or  wholly  wanting  in  an  uninjured  mus- 
cle by  a  very  artificial  hypothesis  as  to  a  so-called  parelectronomic 
region  at  the  place  where  the  ends  of  the  muscle  come  into  contact 
with  the  tendons.  His  theory  of  electrotonus  and  of  the  negative 
variation  of  the  nerve-current  is  too  complicated  and  doubtful  to 
be  even  stated  here  ;  it  is  enough  to  say  that  his  assumptions  as  to 
"peripolar"  and  "bipolar"  molecules,  and  the  efiect  of  the  elec- 
trical current  in  reversing  the  molecules,  etc.,  have  little  to  com- 
mend them  to  the  practical  workers  in  modern  physics. 

§  10.  The  theory  which  Hermann,'  and  those  who  agree  with 
him,  would  substitute  for  the  theory  of  du  Bois-Reymond  takes 
its  point  of  starting  from  a  discovery  made  by  Matteucci  some 
years  ago.  In  1863  this  truly  great  investigator  noticed  phenom- 
ena similar  to  those  of  the  electrotonic  condition  of  the  nerves  in 
over-spun  wires  moistened  with  a  conducting  fluid.  If  an  electri- 
cal current  is  conducted  to  the  moist  covering  of  such  a  wire,  the 
needle  of  the  galvanometer  shows  along  every  part  of  the  wire  the 
presence  of  a  current  in  the  same  direction  with  the  primary  cur- 
rent, but  with  the  strength  of  the  former  diminishing  as  the  dis- 
tance increases  fi'om  the  points  where  the  latter  is  applied  to  the 
wire.  No  such  cun-ent  arises,  however,  if  the  wire  is  made  of  amal- 
gamated zinc  and  its  covering  is  moistened  with  a  solution  of  sul- 
phate of  zinc.  It  appears,  then,  that  the  electrical  condition  of  the 
wire,  when  a  current  is  conducted  to  it,  depends  upon  the  limiting 
surfaces  of  its  metal  centre  and  of  its  moistened  covering  being  po- 
larizable.  Very  recently  ^  Hermann  has,  as  he  thinks,  still  further 
shown  the  possibility  of  explaining  all  the  electrotonic  properties 
of  the  nerves  after  the  analogy  of  Matteucci's  discovery.  A  con- 
ductor consisting  of  a  central  and  a  covering  substance,  with  polar- 
izable  hmiting  surfaces,  as  soon  as  a  momentary  electiic  current  is 
conducted  through  any  portion  of  it  begins  successively  to  exhibit 
a  current  of  the  same  kind  at  every  other  place  in  it  ;  the  more 
•  distant  the  place  from  the  one  to  which  the  cui-rent  is  applied  the 
later  its  appearance  there,  so  that  at  the  most  distant  places  such 
current  may  begin  after  it  has  for  some  time  ceased  at  the  primary 
place.  Now,  in  an  analogous  manner,  every  nerve-fibre  may  be  as- 
sumed to  consist  of  a  centre  and  covering  substance,  with  polarizable 
limiting  surfaces.  In  the  nerve-fibre  the  limiting  surfaces  needed 
for  the  theory  are  j)erhaps  actually  to  be  found  between  the  axis- 

'  The  views  of  Hermann  may  be  found  in  liis  Untersucliungen  znr  Physiol- 
ogie  d.  Muskeln  u.  Nerven,  1867-68,  and  in  numerous  later  papers  in  PfliigerV 
Archiv. 

^  Pfliiger's  Arcliiv,  1885,  xxxv.,  p.  23  f. 


THE   THEORY    OF   HERM AISTIST.  229 

cylinder  and  the  medullary  sheatli.  Griinliagen,'  however,  affirms 
that  the  polarization  of  the  limiting  surfaces  of  the  nerve-fibre  is  a 
consequence  rather  than  a  cause  of  the  current  in  electrotonus. 
The  first  and  fundamental  cause  of  this  current  he  considers  to  be 
the  characteristic  difference  in  the  resistance,  as  conductors,  of  the 
kernel  and  the  covering  of  the  nerve-stretch. 

The  so-called  "  natural  current,"  or  "  current  of  rest,"  Hermann 
does  not  consider  it  necessary  to  explain.  What  appears  to  be  a 
natural  current  Hermann  holds  to  be  in  all  cases  the  result  of  in- 
jury. It  is  to  be  considered,  then,  as  due  to  the  peculiar  molecu- 
lar condition  into  w^hich  certain  parts  of  a  nerve-stretch  are  thrown 
by  their  mechanical  or  chemical  destruction.  In  fact,  whenever  a 
nerve  is  cut  across,  or  any  of  its  fibres  are  injured,  the  molecules 
thus  disturbed  begin  at  once  to  die  ;  they  then  become  negative  to- 
ward the  other  uninjured  parts  of  the  nerve.  It  is  because  of  this 
change  in  the  dying  molecules  that  the  electrical  current  is  devel- 
oped. But  all  the  parts  of  a  wholly  untouched  and  unexcited  nerve 
are,  according  to  Hermann,  "  isoelectric."  It  is  not  necessary  to 
give  the  experimental  evidence  by  which  this  investigator  strives 
to  prove  his  opinion  ;  it  is  enough  to  say  that  this  evidence  is 
strong,  and  nearly,  if  not  quite,  conclusive. 

Accordingly',  Hermann  regards  the  negative  variation  as  not  due 
to  the  diminution  of  any  current  previously  existing,  but  rather  as 
a  manifestation  of  the  electro-motive  forces  which  come  into  opera- 
tion at  the  moment,  and  at  the  seat,  of  excitation.  This  current  is, 
therefore,  the  only  true  "  current  of  action."  Its  rise  and  flow  are 
explained  by  the  fact  that  every  excited  part  of  a  nerve-stretch  be- 
comes negative  toward  all  the  other  parts.  As  this  wave  passes 
along  the  nerve-fibre,  each  minute  portion  becomes  first  negative 
and  then  positive  toward  the  adjoining  minute  portions  ;  and  hence 
the  so-called  "ad-terminal"  and  "ab-terminal  currents"  appear 
along  the  nerve-stretch  as  fast  as  successive  parts  of  its  substance 
reach  their  maximum  of  negativity.  The  excess  of  the  ab-terminal 
over  the  ad-terminal  current  manifests  itself  as  the  so-called  '^'■neg- 
ative variation." 

The  phenomena  of  electrotonus  Hermann  explains,  as  has  already 
been  said,  upon  the  basis  of  Matteucci's  experiments.  An  inner 
polarization,  such  as  takes  place  between  the  wire  and  its  moist- 
ened covering,  takes  place  between  the  substance  which  constitutes 
the  core  of  the  nerve  and  one  of  its  sheaths.  The  electrotonic  cur- 
rent is,  therefore,  simply  due  to  an  escape  of  the  polarizing  cur- 
rent. It  is  wanting  in  the  dead  nerve,  because  the  inner  polariza- 
'  Pfliiger's  Archiv,  xxxv.,  p.  534  f. 


2S0  THE   ELECTEICAL   THEORIES. 

tion  belongs  only  to  the  nerve  in  its  living  state  ;  it  is  stopped  bj 
ligature  or  by  crusbing,  because  the  nervous  substance  is  thus 
made  into  dead,  indifferent  substance,  and  the  functional  continu- 
ity of  the  nervous  core  is  destroyed.  His  detailed  explanation  of 
"  tetanic  action-currents  "  and  "  phasic  action-currents,"  and  of  the 
jDhysiological  phenomena  of  electrotonus  and  catelectrotonus,  need 
not  be  repeated.  The  one  principle  to  which  Hermann  -would  re- 
duce all  the  electrical  j)henomena  derived  from  the  cut  nerve- 
stretch  is  this  :  All  excitable  j^^otoplasm,  when  dying  or  irritated, 
becomes  negative  toward  its  own  univjured  and  unirritated  parts. 
Such  is  the  nature  of  its  electro-motive  reaction. 

§  11.  Objections  have  been  made  to  the  theory  of  Hermann,  but 
they  can  scarcely  be  said  to  be  so  formidable  as  those  which  he 
brings  against  the  theory  of  du  Bois-Keymond.  The  most  forcible  of 
them  is,  perhaps,  the  following :  If  the  so-called  currents  of  rest  were 
due  solely  to  the  negativity  of  the  dying  jjortion  of  the  substance, 
we  should  not  expect  that  the  current  from  the  equator  to  the  cross- 
section  would  be  greater  than  the  current  from  a  point  nearer  the 
cross- section,  seeing  that  the  resistance  is  greater  in  the  former  case. 

Hermann  is  himself  ready  to  admit,'  however,  that  no  simple 
scheme  of  polarization  will  fully  satisfy  the  conditions  of  the  prob- 
lem offered  by  the  behavior  of  the  nerve-muscle  machine  under 
electrical  stimulation.  "  The  platinum  wire,  with  its  moist  sheaths, 
is  no  model  of  the  irritable  nerve  ;  it  is  only  a  model  of  its  elec- 
trotonic  properties."  We  must,  therefore,  after  the  discussion  of 
all  analogies  resort  again  to  the  unknown  molecular  constitution 
and  properties  of  the  substance  of  the  nerve,  as  being  sui  generis, 
for  oui'  explanation  of  its  peculiar  physiological  properties.  Its 
functions  are  a  species  of  molecular  change,  connected,  to  be  sure, 
both  with  chemical  changes  and  with  other  mechanical  changes  of 
a  wave-like  character,  and  yet  unlike  them  all ;  and  these  molecular 
changes,  when  the  nerve  is  excited,  ai^e  propagated  from  point  to 
point  along  its  course  with  a  speed  and  according  to  laws  which 
have  already  been  stated  (see  Chapter  IH.).  But  further  than  this 
we  cannot  as  yet  go  with  confidence  in  af&rming  a  mechanical  the- 
ory of  even  that  simplest  element  of  the  nervous  mechanism  for  ex- 
perimental purposes — namely,  the  nerve  attached  to  the  muscle 
and  constituting  the  nerve-muscle  machine.^ 

'  See  Handb.  d.  Physiol.,  II.,  i.,  p.  195  f. 

-  Further  information  upon  the  two  theories  of  Hermann  and  du  Bois-Rey- 
mond  may  be  found  in  Foster's  Text-book  of  Physiology,  pp.  101  ff.  See,  also, 
a  brief  statement  of  Hermann's  theory  in  the  Journal  of  Physiology,  I.,  pp, 
196-213. 


THE   THEORY    OF   WUISTDT.  231 

§  12.  A  confession  of  ignorance  might  fitly  close  the  entire  dis- 
cussion as  to  the  possibility  at  present  of  a  precise  mechanical 
theory  of  the  nervous  system.  For  on  resuming  the  larger  and 
more  Complicated  inquiry,  as  to  how  the  physiological  functions  of 
all  the  nervous  organs  in  their  mutual  relations  may  be  explained 
according  to  any  known  laws  of  molecular  science,  we  are  obliged 
to  approach  this  inquiry  with  an  acknowledged  inability  to  deal 
satisfactorily  even  with  the  much  simpler  case  of  one  of  the  ele- 
ments of  this  system.  The  peculiar  forms  and  laws  of  the  molec- 
ular activity  of  the  entire  nervous  mechanism  certainly  cannot  be 
understood  until  we  are  able  to  describe  and  explain  the  molecu- 
lar activity  of  a  single  nerve-muscle  machine.  A  statement  of  an 
elaborate  theory,  framed  with  a  view  to  meet  the  whole  case,  by  a 
distinguished  authority,  cannot  fail,  however,  to  possess  a  certain 
interest  and  value.  Accordingly,  we  shall  refer  briefly  to  the 
theory  of  Wundt.^ 

Wundt  begins  his  discussion  of  the  mechanics  (or  molecular 
physics)  of  nervous  substance  by  stating  two  possible  ways  of  ap- 
proaching the  subject.  It  is  conceivable  that  we  might  directly 
investigate  the  chemical  and  physical  constitution  of  the  nervous 
elements,  and  the  changes  they  undergo  in  the  exercise  of  their 
physiological  functions,  with  a  view  to  construct  a  theory  of  so- 
called  nerve-force  by  induction  from  such  investigation.  But  the 
preferable — because  the  much  more  promising — way  of  procedure 
is  to  assume  that  the  processes  which  take  place  in  the  nervous 
system  are  modes  of  molecular  motion  connected  with  each  other, 
and  with  the  forces  of  external  nature,  under  the  general  principles 
of  molecular  physics  ;  and  then,  arguing  deductively^  to  make  such 
a  combination  and  application  of  these  principles  as  will  serve  to 
meet  all  the  demands  of  the  case.  It  scarcely  need  be  said  that 
Wundt  adopts  the  latter  method. 

Assuming,  then,  the  general  principles  of  molecular  physics,  and 
especially  the  lav/  of  the  conservation  of  energy,  it  is  possible  to 
show  how  living  beings  may  be  brought  under  the  control  of  these 
principles.  Such  beings,  through  the  regularity  with  which  the 
making  and  breaking  of  chemical  combinations  goes  on  within 
them,  take  a  noteworthy  part  in  the  continuous  process  of  inter- 
changing potential  and  kinetic  (inner  and  external)  energy.  It  is 
the  nervous  system,  in  all  the  animals  that  have  one,  from  which 

'To  be  found,  in  part,  in  his  Untersuchungen  zur  Mechanik  der  Nerven, 
and  in  later  and  more  complete  form  in  the  chapter  (vi.,  Part  I.)  "  Physio- 
logische  Mechanik  der  Nervensubstanz,"  in  his  Grundziige  der  physioiogi- 
schen  Psychologie.     Leipzig,  1880. 


232  THEORY   OF   MOLECULAR  ENERGIES. 

this  process  is  controlled.  The  process  itself  is  a  species  of  com- 
bustion  ;  the  nervous  system  keeps  going  those  functions  which 
effect  the  process,  regulates  the  setting  free  and  distributing  of 
the  heat,  and  determines  the  muscles  to  movement.  The  source 
of  the  special  activities  of  the  nervous  system  itself  lies  in  the  nat- 
ure of  the  chemical  combinations  which  compose  it. 

The  nervous  system  regarded  as  unaffected  by  stimuli — that  is, 
as  unexcited — may  be  theoretically  compared  to  a  fluid  in  a  condi- 
tion of  equilibrium.  But,  in  fact,  the  nervous  system  is  never  in  a 
condition  of  perfect  equilibrium.  For,  not  only  is  there  a  ceaseless 
play  of  energy  internal  to  this  system,  in  which  the  atoms  separate 
from  the  old  combinations  as  nervous  substance  to  form  new  com- 
binations as  the  same  substance ;  but  a  continuous  process  also 
goes  on  by  which  the  molecules  of  the  nervous  substance  are  broken 
up  to  form  less  complex  but  more  stable  compounds.  Moreover, 
the  building  of  the  nervous  substance  itself  out  of  the  nourishment 
brought  tc  it  is  a  process  the  reverse  of  that  last  mentioned ;  it 
is  a  process,  that  is  to  say,  in  which  the  more  stable  chemical  com- 
pounds of  other  substance  are  broken  up  and  their  atoms  used  to 
form  the  more  complex  but  more  unstable  molecules  of  the  nervous 
substance.  The  process  of  change  from  the  less  stable  to  the  more 
stable  combinations  represents  the  setting-free  of  stored  or  poten- 
tial energy  ;  the  reverse  j)rocess  represents  the  storing  of  energy 
and  the  vanishing  of  kinetic  or  actual  energy.  That  energy  which 
is  made  apparent  by  the  former  process  Wundt  calls  "positive;" 
that  which  is  stored  xip,  when  the  more  stable  combination  disap- 
pears, he  calls  "negative."  Positive  molecular  energy  of  the  ner- 
vous system  is  recognized  as  heat  set  free,  as  contraction  of  the 
muscles,  etc.  ;  its  negative  molecular  energy  exists  in  the  form  of 
heat  becoming  latent,  or  of  inhibitory  action  upon  the  course  of 
excitation  in  the  nerves,  etc. 

In  accordance  with  the  foregoing  theory  of  positive  and  negative 
molecular  energy,  as  due  to  the  chemical  activity  of  the  nervous 
substance,  Wundt  would  explain  the  process  of  excitation  and  con- 
duction in  the  nerve-fibres.  No  simple  conduction  of  motion,  of 
course,  takes  place  in  the  nerve  ;  but  certain  molecular  processes, 
peculiar  to  the  constitution  of  the  nerve,  are  set  up  at  one  point  by 
the  stimulus,  and  are  then  conducted  successively  to  other  points 
along  its  stretch.  In  all  cases  when  a  nerve  is  irritated  two  classes 
of  opjDosed  effects  are  set  up  in  its  substance  ;  the  one  is  directed 
toward  the  production  of  external  energy  (seci'etion,  stimulation  of 
the  gaijglion-cells,  movement  of  the  muscles,  etc.),  the  other  toward 
the  control  of  the  energy  thus  set  free.     The  former  is  positive, 


'      POSITIVE   AND   NEGATIVE   ENERGY.  233 

the  latter  negative  or  inhibitory.  The  general  law  for  all  excita- 
tion of  the  nerves  is,  that  by  the  application  of  stimulus  the  posi- 
tive as  well  as  the  negative  molecular  energy  of  the  nervous  sub- 
stance is  increased.  Stimulating  the  nei've  accelerates  both  the 
recombination  of  the  atoms  of  its  highly  complex  molecules  in 
less  complex  but  more  stable  forms,  and  also  the  escape  of  the 
atoms  from  these  forms  and  their  return  to  the  more  complex  and 
less  stable  combinations.  The  i*enewal  of  the  nerve  depends  upon 
the  i-estitution  of  the  more  complex  molecules  ;  but  the  work 
which  the  nerve  does  external  to  itself  depends  upon  that  process 
of  combustion  in  which  the  complex  molecules  break  up  and  pass 
into  more  stable  but  less  complex  forms.  The  latter  process 
involves,  of  course,  the  exhaustion  of  the  nerve.  External  energy 
(work  done  outside  of  the  nerve)  can  then  only  take  place  in  case 
the  positive  molecular  energy  is  more  accelerated  than  the  negative, 
by  the  application  of  the  stimulus. 

The  entire  sum  of  positive  molecular  energy  which  is  set  free 
when  a  nerve  is  ii'ritated  may  be  reckoned  as  distributed  in  three 
directions  :  a  part  is  spent  in  the  continuous  excitation  of  the 
nerve  ;  another  part  becomes  heat ;  still  another  part  is  converted 
into  negative  molecular  energy.  In  this  way  the  peculiar  molec- 
ular condition  which  the  nerve-fibre  leading  from  the  peripheral 
region  assumes,  when  it  is  irritated,  is  imparted  to  the  central  re- 
gion of  the  nerve-cell. 

§  13.  The  application  of  the  foregoing  theory  to  the  central 
organs  of  the  nervous  mechanism  requires  us  to  take  account  of 
the  fact  that  a  greater  intensity  of  the  stimulus  is  needed  to  move 
a  muscle  through  a  collection  of  ganglion-cells  than  directly  by 
stimulating  the  nerve-fibre  connected  with  the  muscle.  We  are  to 
conclude,  then,  that  the  nervous  substance  of  the  central  parts 
offers  a  far  greater  resistance  to  the  conduction  of  the  jDi'ocess  of 
excitation  than  is  offered  by  the  nerves  themselves.  On  the  other 
hand,  the  central  organs  are  in  a  condition  to  develop  within  them- 
selves a  far  greater  amount  of  work  ;  that  is,  to  convert  into 
kinetic  form  a  vast  sum  of  energy  stored  in  their  chemical  con- 
stitution. The  proofs  which  "Wundt  brings  forward  for  this  view 
are  derived  from  the  phenomena  of  summation  of  inhibition,  and 
of  so-called  "reflex-poisons,"  etc.  A  detailed  discussion  of  such 
phenomena  leads  to  the  conclusion  that,  when  "  summation  "  (com- 
pare pp.  223  ff.)  takes  place,  the  several  excitations  along  the  cen- 
tripetal tracts  have  been  conducted  to  different  sensory  central 
regions,  and  have  then  passed  from  them,  as  a  result  of  their  being 
simultaneously  excited,  over  into  the  same  motor  elements  of  the 


234  THEORY    OF   MOLECtJLAE   ENEEGIES. 

central  organ;  but  when  "inhibition"  takes  place,  such  excitations 
have  been  conducted  so  as  to  come  together  and  counteract  each 
other  in  the  same  sensory  central  region.  The  external  conditions 
of  those  relations  which  obtain  among  the  different  senses  and 
sensations  are  to  be  found,  partly  in  the  constitution  of  the  organs 
of  sense,  and  partly  in  the  nature  of  their  respective  stimuli. 

When  speculating  as  to  the  molecular  changes,  with  respect  both 
to  positive  and  also  to  negative  energy,  which  take  place  in  the 
central  organs,  our  point  of  starting  must  be  taken  from  a  condition 
of  equilibrium  assumed  to  exist  in  their  ganglion-cells.  Excitation 
of  the  central  organs,  like  irritation  of  the  nerves,  increases  both 
kinds  of  nervous  energy.  But  the  positive  molecular  energy  of  the 
central  organs  is  relatively  little  increased  by  a  momentary  excita- 
tion. The  result  of  repeated  excitation,  however,  is  to  make  the 
positive  condition  largely  predominate  in  the  whole  central  region. 
An  excited  ganglion-cell  is  in  a  condition  analogous  to  that  of  the 
nerve-stretch  at  the  anode  when  a  constant  current  is  passing 
through  it.  In  the  nerve,  as  a  rule,  the  nervous  substance  is  used 
up,  and  the  process  of  storing  energy  goes  on  in  only  a  very  par- 
tial manner.  In  the  cells  the  production  of  the  complex  molecules 
in  which  energy  is  stored  predominates,  as  a  rule. 

The  fundamental  properties  of  nervous  matter — mechanically 
considered — are  (1)  to  receive  external  impressions  in  order  by 
them  to  be  determined  in  its  own  molecular  condition  ;  and  (2)  to 
transform  potential  energy  into  kinetic,  partly  under  the  immedi- 
ate, and  partly  under  the  progressive,  influence  of  these  impres- 
sions. 

Wundt  also  proposes  an  elaborate  and  highly  speculative  view 
of  the  molecular  constitution  and  functions  of  the  ganglion-cells. 
Every  such  cell  possesses,  he  thinks,  two  regions  (although  the 
word  "  regions "  is  not  to  be  interpreted  locally).  These  regions 
are  called  "peripheral "  and  "central,"  because  the  former  is  as- 
sumed to  stand  in  more  intimate  x-elations  to  the  peripheral  ner- 
vous substance,  with  respect  to  its  own  reactions  under  stimula- 
tion. Excitations  which  reach  the  central  region  of  a  ganglion-cell 
induce  a  propagation  of  the  processes  set  up  in  this  region  to  the 
other  or  peripheral  region.  In  the  same  way  do  excitations  which 
first  touch  the  peripheral  region  necessitate  the  spreading  of  the 
form  of  molecular  energy  set  free  here  over  into  the  central  region. 
When  a  process  of  excitation  is  frequently  conducted  in  a  definite 
direction  through  some  ganglion-cell,  such  direction  is  favorably 
disposed  toward  the  conduction  of  future  excitations  which  may 
reach  the  same  cell.     Whether  the  excitation   of  any  particular 


'ACTIOT^   DEPENDENT   ON   STRUCTURE.  235 

nerve-fibre  connected  with  a  ganglion-cell  results  in  an  excitatory  or 
an  inhibitory  effect  depends  upon  the  nature  of  its  connection  with 
the  cell. 

But  we  refrain  from  further  statement  of  a  theory  so  largely  con- 
jectural. Nothing  i-emains  but  to  repeat  a  confession  of  igno- 
rance and  of  inability  even  to  suggest  a  satisfactory  solution  for  so 
complex  a  problem  in  molecular  physics  as  is  offered  by  the  human 
nervous  system. 

§  14  A  review  of  various  molecular  theories  proj)osed  to  account 
for  the  nervous  mechanism,  either  as  a  whole  or  in  any  of  its  parts, 
makes  plain  the  important  fact  that  such  theories  are  all  obliged 
to  assume  the  origin  and  continuance  of  a  peculiar  molecular 
structure  for  this  mechanism.  In  other  words,  no  attempt  to 
explain  how  the  nervous  system  acts  can  avoid  the  conclusion  that 
the  determining  factor  in  the  explanation  must  be  found  in  what 
the  nervous  system  is.  The  physiological  functions  of  the  nerve 
depart  when  the  nerve  dies.  The  nerve  dies  when  it  is  severed 
from  the  ganglion-cell.  Both  cell  and  nerve  must,  therefore,  con- 
stitute a  living  molecular  unity,  in  order  that  their  normal  physio- 
logical functions  may  be  performed.  The  explanation  of  these 
functions  assumes  the  molecular  constitution  of  the  organs  them- 
selves. But  how  shall  we  explain,  in  accordance  with  the  known 
laws  of  molecular  physics,  the  origin  and  preservation  of  such  a  mo- 
lecular constitution  ?  It  is  the  business  of  biology  rather  than  of 
physiology  to  attempt  an  answer  to  this  question.  But  the  question 
itself  asks  from  science  the  performance  of  a  task  no  smaller  than 
that  of  framing  a  mechanical  theory  of  life.  Biological  science  can, 
as  yet,  do  little  toward  framing  such  a  theory.  Throughout  our  en- 
tire discussion  of  the  nervous  mechanism  we  have  carefully  avoided 
raising  an  inquiry  as  to  the  nature  of  life,  as  to  the  source  and  con- 
ditions of  that  very  molecular  constitution  which  determines  the 
nature  and  working  of  this  mechanism.  We  have  simply  assumed 
and  argued  that,  taking  the  nervous  system  for  what  it  really  is 
and  really  does,  its  structure  and  functions  admit  of  scientific  ex- 
planation, so  far  as  such  explanation  is  possible  at  all,  only  when 
they  are  regarded  as  belonging  to  a  molecular  mechanism.  The 
question  of  a  mechanical  theory  for  the  origin  and  constitution  of 
living  organisms  in  general  lies  outside  of  the  inquiries  of  Physio- 
logical Psychology. 

§  15.  One  other  important  question  has  also  thus  far  been 
avoided.  What  is  the  relation  of  the  mind  to  the  working  of  the 
nervous  mechanism  ?  Can  the  mind  set  this  molecular  mechanism 
at  work,  or  can  it  in  any  way  determine  the  character  of  its  func- 


236  THEOEY   OF   MOLECULAE   ENEEGIES. 

tions  ?  As  far  as  our  consideration  of  the  nervous  system  has  gone 
hitherto,  all  might  very  well  have  been  the  same  without  the  exist- 
ence of  a  single  act  of  conscious  thought  or  feeling  occurring  in 
any  relation  whatever  to  this  system.  Given  the  molecular  mechan- 
ism as  it  is  constituted  and  conserved  by  the  forces  which  control 
as  long  as  life  continues ;  and  given  the  necessary  impact  of  out- 
side forces  ujDon  the  end-organs,  and  the  projDer  changes  of  blood 
within  the  central  organs  ;  and  it  has  been  assumed  that  this  mech- 
anism would  exercise  its  functions  in  ways  thus  far  described. 
But  the  consideration  of  another  class  of  phenomena  is  now  to  be 
introduced  ;  these  are  the  phenomena  of  human  consciousness,  the 
phenomena  of  3Iind.  The  question  whether  such  phenomena  can 
be  true  causes  of  any  of  the  changes  in  the  molecular  mechanism 
is  a  part  of  the  general  question  as  to  the  correlations  that  exist 
between  two  classes  of  facts.  The  answer  to  such  general  question 
belongs  to  the  following  divisions  of  our  work. 


PART  SECOND. 


CORRELATIONS  OF  THE  NERVOUS 
MECHANISM  AND  THE  MIND. 


CHAPTER  I. 
THE  LOCALIZATION  OF  CEEEBEAL  FUNCTION. 

§  1.  Ordinaey  observation  recognizes  the  fact  that  the  phenomena 
of  consciousness  are  more  or  less  definitely  correlated  with  the 
condition  of  the  body.  Certain  alterations  in  our  mental  states,  on 
account  of  the  injury  of  any  of  its  masses,  as  well  as  a  constant  de- 
pendence of  those  states  upon  the  way  some  of  the  masses  stand 
related  to  each  other  and  to  the  outside  world,  impress  the  fact  upon 
our  daily  experience.  It  is  by  no  means  so  obvious  that  the  ner- 
vous substance  has  any  peculiar  relation  to  the  thoughts  and  feelings 
of  the  mind.  For  the  functions  of  the  nervous  system  are  not  ex- 
ercised in  giving  information  as  to  itself,  its  own  condition  and 
changes.  By  aid  of  these  functions  we  have  presented  in  con- 
sciousness a  more  or  less  clear  picture  of  the  condition  and  changes 
of  the  superficial  parts  of  the  body.  In  the  same  way  a  knowledge 
is  gained  of  the  successive  states  of  tension  belonging  to  the 
muscles  in  movement,  and  even — though  rather  obscurely — of  the 
place  and  condition  of  the  internal  organs.  But  as  long  as  they 
are  healthy  and  excited  with  only  a  moderate  intensity  of  their 
stimuli,  the  nerves  do  not  even  reveal  their  own  existence ;  and 
when  they  are  injured  or  unduly  excited,  the  notice  they  furnish 
of  the  fact  comes  in  the  form  of  painful  feeling  which  we  have 
learned  to  localize,  not  in  the  nervous  substance  itself  but  in  the 
adjacent  parts  of  muscle  and  skin.  Attention  may  be  called,  how- 
ever, to  the  peripheral  nerves  by  the  accident  or  the  dissecting- 
knife  which  exposes  them  to  sight.  In  the  case  of  the  central 
nervous  organs,  and  especially  in  the  case  of  the  brain,  there  is  little 
in  ordinary  experience  which  leads  to  a  suspicion  of  their  signifi- 
cance or  even  of  their  existence. 

It  is  not  very  strange,  then,  that  no  general  recognition  of  the 
supreme  importance  of  the  brain,  in  relation  to  the  phenomena  of 
consciousness,  is  to  be  found  in  early  history.  It  is  true  that 
Plutarch  '   and  Theophrastus  "   inform  us  of  the  opinion  of  the 

'  DePlacitis  Philosophorum,  IV.,  17,  1. 
'  De  Sensu,  §  35  f. 


240  GENERAL   FUNCTIOlSr   OF   THE   BRAIlsr. 

pliysieian  Alcmaeon,  who  is  said  to  have  been  a  younger  contem- 
porary of  Pythagoras,  and  who  regarded  the  brain  as  the  common 
meeting-place  of  the  senses.  The  same  view  is  also  ascribed  to  the 
celebrated  Hippocrates.  Later  on  Plato  accepted  it.  But  Aris- 
totle,' the  greatest  of  all  thinkers  in  antiquit}',  the  son  of  a  phy- 
sician, especially  educated  in  physical  science,  and  well  acquainted 
for  the  time  in  the  dissection  of  animals,  regarded  the  brain  as  a 
lump  of  cold  substance,  quite  unfit  to  be  the  seat  and  organ  of  the 
sensus  communis.  This  important  office  he  ascribed  rather  to  the 
heart.  The  brain  he  considered  to  be  chiefly  useful  as  the  source 
of  fluid  for  lubricating  the  eyes,  etc. 

§  2.  The  opinion  of  Exner,"  however,  who  supposes  that  feeling 
in  no  way  immediately  informs  us  that  we  think  with  the  head, 
still  less  with  the  brain  or  the  cortex  of  the  cerebrum,  seems  some- 
what extreme.  Concerning  the  contents  oi  the  cranial  cavity,  indeed, 
we  get  no  direct  information  from  the  feelings  connected  with 
the  exercise  of  its  functions.  But  we  certainly  localize  in  the  head 
certain  phenomena  of  consciousness  that  are  inextricably  inter- 
woven with  the  processes  of  thought.  The  act  of  attention  results 
in  feelings  which  indicate  that  the  muscles  of  the  eye  are  being  in- 
nervated ;  or  in  the  more  indefinite  and  diffused  sense  of  strain 
produced  by  contracting  the  skin  of  the  forehead  and  adjacent 
parts  of  the  face.  The  special  sensations  of  hearing,  smelling,  and 
tasting,  which  impress  so  strongl}^  our  conscious  life,  are  frequently 
referred  to  the  head.  The  same  thing  is  true  of  many  of  the  sen- 
sations of  sight — particularly  of  such  as  appear  when  the  eyes  are 
closed,  in  the  form  of  after-images,  or  spectra,  or  indefinite  and 
changing  color-spots,  seated  in  the  upper  front  part  of  the  face. 
Moreover,  that  inchoate  and  sometimes  half-articulated  language, 
with  which  we  support  our  ti'ains  of  thought,  even  when  we  are  not 
conscious  of  resortiog  to  the  expedient  of  "  talking  to  ourselves,"  is 
felt  to  be  going  on  within  the  head.  When  one  has  been  engaged 
for  some  time  in  intense  thought,  or  in  eager  and  concentrated 
observation,  one  is  suddenly  made  aware  of  more  or  less  painful 
feelings  which  are  somewhat  indefinitely  ascribed  to  the  same 
cerebral  region.  Men  commonly  lean  the  head  upon  the  hand 
in  supporting  meditation  ;  or  rub  it  vigorously  to  awaken 
the  powers  of  memory  and  reasoning  ;  or  stroke  it  to  relieve  the 
disagreeable  sensations  which  follow  severe  mental  excitement. 
Headache,  of  more  or  less  intensity,  thus  becomes  associated  with 

1  See  De  Partibiis  Animalium,  052.  b.  5;  (II.,  7);  656,  b.   22  (II.,   10);  De 
Juvent. ,  4(!7,  b.  28  ;  and  De  Anima.  III.,  1  and  2. 
'  See  Hermann's  Haudb.  d.  Physiol.,  II.,  ii.,  p.  193. 


NEED    OF  AETERIAL   BLOOD.  241 

"active  exercise  of  the  intellect.  The  head  is  wearied  with  thought ; 
and  not  only  so,  but  also  with  intense  physical  exercise.  The  dis- 
comfort which  bodily  strain  produces  in  the  hinder  regions  of  the 
head  are  an  indication,  although  of  only  a  very  general  kind,  that 
processes  have  gone  on  in  that  locality  which  are  of  great  impor- 
tance to  the  succeeding  states  of  consciousness.  All  this  apparent 
testimony  of  immediate  feeling  is,  doubtless,  somewhat  exaggerated 
in  an  age  so  distinctively  "  nervous"  as  our  own  ;  and  this  fact  may, 
perhaps,  account  in  part  for  the  inclination  of  the  ancients  to  em- 
phasize the  more  obvious  connection  of  mental  jDhenomena  with  the 
heart,  and  other  lower  visceral  organs,  to  the  neglect  of  all  connection 
of  these  phenomena  with  the  brain.  But  it  cannot  well  be  doubted 
that  a  certain  amount  of  testimony  from  immediate  feeling  as  to  the 
important  relation  which  exists  between  the  state  of  mind  and  the 
contents  of  the  cranial  cavity,  belongs  to  all  human  experience. 

However  uncertain  the  witness  of  immediate  feeling  upon  the 
point  in  question  may  be,  very  little  observation  of  others  is  needed 
to  amplify  and  confirm  its  witness.  We  are  not  infrequently  led  to 
notice  how  quickly  and  profoundly  the  states  of  consciousness  are 
changed  by  injuries  to  the  brain.  The  effect  of  a  blow  upon  the 
head  in  suspending  consciousness  is  decisive  of  this  question.  The 
intimate  local  connection  between  the  organs  of  sense  and  the 
brain  leads  naturally  to  the  conclusion  that  the  avenues  of  sensa- 
tion and  of  perception  have  in  the  latter  a  kind  of  gathering-j)lace, 
as  it  were.  It  is  but  a  step  from  this  conclusion  to  a  recognition 
of  the  truth  that  the  physiological  significance  of  the  contents  of 
the  cranial  cavity  consists  in  their  afibrding  a  field  upon  which  all 
the  impressions  of  sense  can  meet  together,  and  so  furnish  the  basis 
and  material  of  comparative  thought.  Indeed,  it  was  this  line  of  in- 
quiry which  probably  led  certain  ancient  anatomists,  like  Herophilus 
and  Galen,  to  locate  the  soul,  or  psychical  principle,  in  the  brain, 

§  3.  A  great  multitude  of  physical  considerations,  advanced  by 
modern  science,  place  beyond  doubt  the  supreme  importance  of 
the  brain  in  its  influence  upon  the  phenomena  of  consciousness. 
It  has  already  been  stated  (Part  I.,  Chapter  HI.,  §  7)  that  the  free 
circulation  of  arterial  blood,  with  its  supjDly  of  oxygen,  is  a 
necessary  condition  for  the  fulfilment  of  the  functions  of  all  the 
central  organs  ;  this  necessity  is  especially  marked  in  the  case  of 
the  brain.  The  stoppage  of  one  of  the  great  arteries  leading  to 
this  organ,  either  by  compression  in  the  neck,  or  by  embolism  at 
some  point  along  its  course,  at  once  produces  profound  dis- 
turbances and  even  complete  cessation  of  consciousness.  It  has 
been  calculated  that,  while  the  weight  of  the  entire  encephalon  is 
16 


242  GENERAL   FUISrCTION   OF   THE   BRAIN". 

only  about  one-forty-fifth  of  that  of  the  body,  the  supply  of  blood 
used  uj)  there  is  not  less  than  about  one-eighth  of  the  whole  supply. 
This  expenditure  is  indicative  of  the  large  amount  of  work  done 
by  the  intercranial  organs. 

More  delicate  measurements  seem  to  show  that  the  temperature 
rises  and  falls  in  the  whole  cerebral  area,  or  at  particular  cir- 
cumscribed regions  of  the  cortex,  in  close  connection  with  the 
psychical  activities.  Thus  Dr.  Lombard  found,  by  measurements 
with  exact  thermo-electric  apparatus,  that  the  temperature  of  the 
head  during  waking  hours  varies  rapidly,  though  slightly  (less 
than  y^^°  C.)  ;  and  that  these  variations  "  appear  to  be  connected 
with  different  degrees  of  cerebral  activity.  .  .  .  Every  cause 
that  attracts  the  attention — -a  noise,  or  the  sight  of  some  person  or 
other  object — produces  elevation  of  temperature.  An  elevation  of 
temperature  also  occurs  under  the  influence  of  an  emotion,  or 
during  an  interesting  reading  aloud."  Similar  examinations  have 
been  carried  still  further  by  Schiff,'  who  has  appUed  extremely  del- 
icate thermoscopic  instruments  directly  to  the  cerebral  substance 
of  certain  animals  (comp.  Part  I.,  Chapter  III,  §  21).  He  finds 
that  the  arrival  of  sensorial  impressions  is  followed  by  a  rise  of 
temperature,  in  certain  special  areas  of  the  cortical  substance,  where 
— as  he  supposes— these  impressions  are  diffused;  he  also  con- 
cludes that  any  resulting  psychical  activity  is  itself  connected  with 
a  still  further  rise  of  temperature  than  that  which  the  sensorial 
impressions  alone  engender.  Schiff 's  conclusions,  therefore,  point 
not  only  to  the  localization  in  the  entire  brain  of  functions  connected 
with  the  phenomena  of  conscious  psychical  life,  but  also  to  some 
distribution  of  such  functions  among  its  various  areas.  In  the 
same  general  direction  are  the  conclusions  of  Byasson"  and  others, 
as  to  an  increase  of  waste  in  the  tissues  of  this  organ,  which 
corresponds,  to  some  extent,  at  least,  with  the  amount  of  thought 
accomplished.  This  investigator  found  that  the  quantity  of  sul- 
phates and  phosphates  excreted,  in  comparison  with  the  quantity 
estimated  as  entering  into  his  diet,  was  notably  increased  in  pro- 
portion to  the  amount  of  his  mental  work.  That  is  to  say,  in  con- 
nection with  an  increase  in  the  number  and  intensity  of  the 
psychical  operations  stands  an  increase  in  the  functional  activity  of 
the  cerebral  cells,  as  shown  by  the  expenditure  of  their  phos- 
phorized  constituents.^ 

'  Archives  de  Physiologie,  1870,  p.  451. 
''  In  the  Jour,  d,  Anat.  de  Robin,  1869,  p.  557  f. 

'■'  See  the  chapter  of  Luys  on  tlie  Physico-chemical  Phenomena  of  Cere- 
bral Activity  ;  The  Brain  and  its  Functions. 


RELATIVE   WEIGHT   OF   BllATN". 


243 


§  4.  Comparative  anatomy  also  indicates  the  importance  of  the  re- 
lation between  the  size,  structure,  and  functions  of  the  intercranial 
nervous  mass  and  the  jDhenomena  of  mind.  It  shows,  first  of  all,  a 
general  but  indefinite  correspondence  betvs^een  the  size  and  weight 
of  the  brain  of  any  species  of  animal,  as  compared  with  the  weight 
of  its  entire  mass,  and  the  place  of  the  same  species  in  the  scale  of 
intelligence.  This  fact  is  roughly  exhibited  by  the  following  com- 
parative table  :  ^ 


RELATIOiSr    OF   THE    WEIGHT    OF    THE   BRAIN  TO   THE    WEIGHT    OF    THE   BODY. 


Tunny-fish .  . . 
Land  tortoise. 

Shad 

Tadpole 

Elephant  . . . . 
Salamander . . 
Sheep 


1 

37,440 

1 

2,240 

1 

1,837 

1 

720 

1 

500 

1 

380 

1 

351 

Finch 1 

Eagle 1 

Pigeon 1 

Rat 1 

Gibbon 1 

Young  cat 1 

Sai — ape 1 


231 
160 
104 
82 
48 
39 
25 


Doubtless  other  tables  might  be  compiled  which  would  lead  to 
less  satisfactory  conclusions  than  the  one  given  above.  Even  in 
this  table  we  note  that  the  elephant  stands  lower  than  the  sala- 
mander or  the  sheep,  both  of  which  animals  are,  in  fact,  far  in- 
ferior to  the  elephant  in  intelligence.  Large  allowance  must  also 
be  made  in  certain  cases  for  peculiarities  of  physical  structure  ;  for 
example,  the  tortoise  is  rated  lower  than  he  would  be  were  it  not 
for  his  heavy  shell.  The  law  itself  is  confessedly  subject  to  re- 
markable and  unexplained  exceptions  ;  at  best  it  holds  good  only 
in  a  very  general  way.  For  example,  the  relative  weight  of  the 
brain  is  not  greatly  different  in  the  dolphin,  in  the  baboon,  and  in 
man.  It  is  much  greater  in  the  infancy  and  youth  of  the  human 
species  than  in  middle  life  or  old  age.  In  the  male  child  at  birth 
it  is  about  as  one  to  six  or  seven  (according  to  Tiedemann,  1  to 
5.85  in  the  male,  and  1  to  6.5  in  the  female).  The  brain  grows  with 
great  rapidity  for  the  first  few  years — the  increase  during  the  first 
year  being  estimated  at  about  one  cubic  centimeter  daily.  But  the 
rest  of  the  body  increases  so  much  more  rapidly  that  by  the  end  of 
the  second  year  it  is  about  1:14  ;  by  the  end  of  the  third  year,  1:18. 
It  increases  in  absolute  weight  until  well  on  into  middle  life,  and 
then  after  middle  life  diminishes  at  about  the  average  rate  of  one 

'  Taken  from  Hermann's  Handb.  d.  Physiol.,  XL,  ii.,  p.  193.  as  compiled  by 
Exner  on  the  basis  o£  the  works,  in  part  of  Carus,  and  in  part  of  J.  Miiller. 
The  figures  of  comparative  weight  between  the  brain  and  the  body  are  some, 
what  differently  given  by  other  authorities. 


244  GENERAL    FUNCTIOjST    OF    THE   BRAIaST. 

ounce  in  a  decade.  The  average  relative  weight  of  the  adult  brain 
is  one-fortieth  or  one-fiftieth.  Tiedemann  found  that  the  relative 
weight  of  the  brain  is  dependent  upon  the  absolute  weight  of  the 
body,  and  is  relatively  greatest  with  light  persons.  The  human 
brain  is,  however,  absolutely  heavier  than  that  of  any  of  the  ani- 
mals except  the  elephant  (8-10  lbs.)  and  the  whale  (5-6  lbs.). 

Much  pains  has  been  taken,  by  actually  weighing  diiferent 
human  brains,  or  by  calculating  their  weight  on  the  basis  of  careful 
cranial  measurements,  to  establish  a  law  connecting  the  amount  of 
the  iutercranial  nervous  mass  with  the  comparative  intelligence  of 
races  and  of  individuals.'  The  average  weight  of  the  brain  of  the 
adult  European  is,  for  the  male,  fi'om  46  to  52  ounces  ;  for  the  fe- 
male, from  42  to  46  ounces.  Boyd  gives  the  average  weight  of  the 
brain  of  the  male,  at  the  period  of  life  when  it  is  most  developed 
(twenty-five  to  forty  years  of  age),  as  46.8  ounces  (1,321  grams,  91 
centigrams).  This  difference  between  the  sexes  is  not  wholl}'  de- 
pendent on  difference  in  bulk  of  body,  but  is  an  important  sexual 
distinction.  The  brain  of  man  is  on  the  average  ten  per  cent,  above 
that  of  woman  ;  the  difference  in  average  stature  is  about  eight  per 
cent.  Many  human  brains  rise  above  the  upper  average  ranges  ; 
others  fall  below  the  lower  average  ranges  ;  and  yet  no  marked 
peculiarities  of  mental  development  are  necessarily  connected  with 
these  variations.  Considerable  quantities  of  the  substance  of  the 
brain  may  be  lost  (at  any  rate  from  some  areas  of  the  cortical  sur- 
face) without  perceptibly  changing  the  mental  life.  In  278  cases 
of  males,  the  maximum  weight  of  brain  was  found  to  be  65  ounces, 
the  minimum  34  ounces  ;  in  191  cases  of  females,  the  maximum 
was  56  ounces,  the  minimum  31  ounces.'  Numerous  instances  of 
large  excess  in  the  average  weight  of  brain-mass  by  individuals 
eminent  for  intelligence  are  on  record  :  for  example,  Byron  scarcely 
under  79  ounces  ;  Cromwell,  only  77  grains  less,  or  78.8  ounces 
(although  Vulpian  thinks  that  the  national  spirit  has  exaggerated 
both  these  instances)  ;  Cuvier,  64.5  ounces  ;  Abercrombie,  63 
ounces  ;  Spurzheim,  55  ounces  ;  Sir  J.  Y.  Simpson,  54  ounces  ;  Web- 
ster, 53.5  ounces  ;  Agassiz,  53.4  ounces  ;  Chalmers,  53  ounces. 
Other  persons?  of  eminence,  however,  have  had  brains  of  only  aver- 
age, or  of  under  average  weight ;  thus  C.  F.  Hermann,  46.5  ounces, 
and  J.  F.  L.  Hausmann,  43.3  ounces.  Moreover,  brains  of  high 
weight  not  infrequently  occur  without  evidence  of  unusual  mental 
capacity,  or  even  in  the  case  of  those  mentally  inferior.     Kecord  is 

'  On  the  relations  of  the  Brain  witli  respect  to  weight  and  mass,  see  Schwalbe, 
Lehrb.  d.  Neurologie.  ii.,  pp    HSO  ff.      Erlangen,  1881. 

-Results  obtained  by  Sims,  Clendinning,  Tiedemann,  and  J.  Reid. 


BRAIlSrS   OF   DIFFERENT   RACES.  245 

made  of  four  male  brains,  beloBging  to  persons  of  no  repute  for  in- 
tellectual ability,  which  ranged  from  62.75  ounces  to  61  ounces  ;  of 
another  such,  which  weighed  60.75  ounces  ;  of  the  brain  of  a  boy 
of  fourteen  which  weighed  60  ounces.  In  the  West  Riding  Asy- 
lum '  for  the  Insane,  out  of  375  males  examined,  the  weight  of  the 
bi*ain  in  30  cases  was  55  ounces  or  upward  ;  out  of  300  females 
examined,  in  26  cases  it  was  50  ounces  or  upward.  Several  persons 
afflicted  with  dementia  were  found  to  have  brains  weighing  more 
than  60  ounces.  On  the  contrary,  idiots,  almost  without  exception^ 
have  brains  far  below  the  average  in  weight ;  as  a  rule,  the  brain 
of  such  an  unfortunate  does  not  weigh  so  much  as  30  ounces. 
Cases  of  microcephalous  idiots  are  on  record  whose  brains  weighed 
only  10.5,  or  even  8.05  ounces.  Here,  again,  however,  singular  ex- 
ceptions must  be  admitted  ;  for  in  a  few  cases  the  brains  of  idiots 
have  reached  the  average  weight,  and  have  even,  in  rare  cases,  con- 
siderably surpassed  it. 

Although  the  data  adduced  to  show  that  the  average  weight  of 
brain  in  the  more  highly  civilized  races  is  greater  than  in  the  savage 
races,  are  by  no  means  abundant  or  conclusive,  yet  they  are  suffi- 
cient to  create  a  reasonably  strong  presumption  in  favor  of  this 
view.  Calculating  from  the  size  of  the  cranial  cavity,  as  ascertained 
by  measurement  of  a  large  number  of  skulls,  it  is  inferred  that  the 
average  weight  of  brain  in  the  African,  Australian,  and  Oceanic 
races  generally,  falls  from  1  to  4  ounces  below  that  of  the  more 
highly  civilized  European.  It  is  further  noted  that  there  is  almost 
a  complete  absence  of  cases  rising  above  the  higher  ranges — above 
54  ounces,  for  example  ;  and  that  there  is  not  the  same  difference 
between  the  two  sexes  in  the  uncultivated  as  in  the  cultivated, 
peoples.  Davis  calculated  the  average  weight  of  brain  among  the 
Chinese  to  be  about  equal  to  that  of  the  Caucasian  race  in  Europe  ; 
among  the  Sandwich  Islanders  to  be  some  thirty  grams  less.  The 
surpi'isingly  low  weight  of  the  brain  of  the  Hindus  is  in  part  a 
function  of  their  smaller  weight  and  bulk  of  body.  It  ma}'  fairly 
be  urged  in  objection,  that  by  the  method  of  measuring  skulls 
taken  somewhat  at  random  we  should  be  likely  to  find  a  note- 
worthy absence  of  such  exceptional  cases  in  certain  quarters 
among  the  European  races  ;  and  that  the  relative  increase  in  size 
of  the  female  brain  among  uneducated  peoples  is  probably,  in  part 
at  least,  the  result  of  the  response  of  the  nervous  system  to  the 
demand  made  upon  it  for  the  hard  labor  performed  by  the  women 
among  such  peoples. 

Any  law  which  refers  the  intensity  and  range  of  the  mental 
^  For  these  facts  see  the  Encyclopsedia  Britaunica,  uiuth  ed.,  I.,  p.  879  f. 


246  GENERAL   FUNCTION   OF   THE   BRAIN. 

activities  directly  to  the  size  and  weight  of  the  nervous  mass  of  the 
brain  must,  therefore,  be  held  only  very  loosely.  It  is  to  be  ex- 
pected that  many  unexplained  exceptions  will  meet  us,  whether  we 
compare  men  with  the  other  animals,  or  certain  races  of  men 
with  others,  or  individual  men  with  one  another.  No  intelligent 
physiologist  would  now  think  of  making  mere  mass  the  test  of 
mental  capacity. 

§  5.  A  more  intimate  relation  of  dependence  exists  between  the 
amount  of  intelligence  and  the  complex  structure  of  the  brain  as 
arising  to  a  large  extent  from  the  development  of  the  cerebral 
hemispheres — that  is,  from  their  relative  size  and  esjDause,  and 
from  the  number  and  depth  of  their  convolutions.  In  other 
words,  wealth  of  expanded  and  convoluted  cerebral  hemispheres 
is,  in  some  general  way,  a  measure  of  the  richness  and  intensity  of 
mental  life.  This  conviction  becomes  stronger  the  more  carefully 
the  comparative  anatomy  of  the  cerebi^um,  and  the  development  of 
the  cerebral  hemispheres  in  the  human  embryo,  are  examined. 
The  forms  of  brain  found  permanently  in  fishes,  amphibians, 
reptiles,  birds,  and  the  lower  mammals,  are  extremely  similiar  to 
those  shown  in  succession  by  the  developing  brain  of  the  higher 
mammals,  and  especially  of  man.  The  most  distinctive  feature  of 
man's  superior  brain  is  the  marked  development  in  the  size,  num- 
ber, and  depth  of  the  convolutions  of  the  hemispheres.  In  fishes 
generally,  both  cerebrum  and  cerebellum  are  very  small ;  but  the 
ganglia  connected  with  the  organs  of  sense,  especially  of  vision,  are 
relatively  large.  In  amphibia  the  cerebral  hemispheres  are  rel- 
ativel}'  enlarged  ;  are  advanced  backward  still  farther  in  reptiles  ; 
while  in  birds  the  vesicles  of  the  mid-brain  are  partially  hidden  by 
the  development  of  the  hemispheres.  In  the  lower  mammals  the 
enlargement  of  these  same  organs  by  growth  backward  continues, 
and  their  two  parts  become  connected  by  a  commissure  ;  but  they 
still  remain  comparatively  meagre  in  size  and  simple  in  structure, 
without  much  distinction  of  lobes  or  division  into  convolutions.  It 
is  only  in  the  most  elaborately  developed  brains  of  the  higher 
mammals  that  the  occipital  lobe  enlarges  backward  so  as  to  cover 
mid-brain,  cerebellum,  and  medulla  oblongata ;  and  that  the  frontal 
lobe  spreads  forward  over  the  nasal  cavities  so  as  to  constitute  a 
development  of  forehead.  Meantime  the  convolutions  apparent  on 
the  cerebral  surface  increase  in  number  and  depth. 

The  theory  suggested  by  comparative  anatoniy  is  confirmed  by 
the  probable  view  of  Meynert,  that  the  whole  of  this  cortical  I'egion 
of  the  cerebrum  is  a  great  "projection-field"  on  which  the  sensory 
impulses  are  marshalled  and  systematically  ordered  (to  serve,  as  it 


THE   MEASUREMENTS   OF    WAGNER.  247 

Tvere,  for  the  physical  bans  of  mental  phenomena),  as  they  arrive 
from  the  peripheral  regions  and  are  distributed  over  the  outgoing 
motor  tracts.  Certain  striking  exceptions  to  the  principle  of  this 
theory  must,  however,  be  acknowledged.  Within  each  great  group 
of  animals  considerable  variations  occur  in  the  degree  of  cerebral 
convolution,  such  that  it  cannot  be  said  accui-ately  to  measure  the 
degree  of  intelligence.  For  example,  among  mammals  the  in- 
sectivora  have  brains  "poorest"  in  convolutions,  the  herbivora 
are  "richest,"  and  the  carnivora  stand  between;  the  ruminants, 
although  rather  dull  and  incapable  of  being  taught,  have  numer- 
ous and  deep  convolutions  enough  to  rank  them  much  higher  than 
their  real  intelligence  deserves.  The  marmoset,  on  the  other  hand, 
the  relative  weight  of  whose  brain  is  as  1  to  18,  shows  a  compara- 
tively smooth  and  non-convoluted  surface,  in  striking  contrast  with 
that  of  other  monkeys. 

Trustworthy  data  are  as  yet  wanting  to  place  beyond  doubt  the 
probable  opinion  that  the  brains  of  less  highly  civilized  races  and 
less  highly  intellectual  individuals  are  relatively  poor  in  develop- 
ment of  the  cerebral  hemispheres.  The  human  embryo  is,  indeed, 
an  illustration  in  miniature  of  the  truth  of  this  opinion  ;  the  older 
it  becomes  the  more  distinctly  marked  are  the  lobes  of  the  cere- 
bral hemispheres,  and  the  more  numerous  and  deep  are  their  con- 
volutions. The  brains  of  idiots  are  said,  as  a  rule,  to  be  jjoor  in 
convolutions  ;  this  fact  is  doubtless  connected  with  the  embryonic 
condition  in  which  many  of  them  have  remained  through  arrested 
development.  Hermann  Wagner,'  on  the  basis  of  measurements 
made  by  his  father,  undertook  to  estimate  the  comparative  total 
siu'face  of  the  cei'ebral  hemispheres  of  four  brains,  viz.:  of  two 
males  of  noteworthy  intelligence  (Gauss,  the  mathematician,  and 
Fuchs,  the  physician),  of  a  male  laborer  (Krebs),  and  of  a  female 
in  middle  life.  By  weighing  carefully  the  amount  of  gold-foil  laid 
on  uniformly,  which  was  required  completely  and  closely  to  en- 
velop all  the  convolutions  of  these  brains,  Wagner  concluded  that 
the  area  of  concealed  surface  was,  in  each  case,  approximately 
equal  to  that  exposed.  The  total  surfaces  of  the  four  brains  were 
thus  found  to  measure — of  Gauss,  2,196  square  centimeters;  of 
Fuchs,  2,210  ;  of  the  woman,  2,041 ;  of  Krebs,  1,877.  It  is  a  tempt- 
ing but  rather  insecure  generalization  which  concludes  from  so 
sew  cases  that  the  richness  of  the  cerebral  convolutions  (the  total 
surface,  both  that  exposed  and  that  concealed  by  the  sulci),  is  a 
general  direct  measure  of  the  intelligence. 

§  6.  Other  interesting  attempts  have  been  made  to  measure  the 
1  Maassbestimmuiigen  d.  Oberflaclie  d.  grossen  Geliiriis.     Cassel,  1864. 


248  GENERAL   FUNCTIOlSr   OF   THE   BEAIlSr. 

intelligence  of  the  animal  by  the  relative  size  and  structure  of 
the  iutercranial  nervous  mass,  and  so,  definitely,  to  establish  a  dii^ect 
relation  between  the  two  ;  we  notice  especially  those  of  J.  Miiller,' 
and  of  Meynert.^  The  great  physiologist,  Miiller,  held  that  the 
position  of  an  animal  in  the  scale  of  intelligence  may  be  estimated 
by  comparing  the  hemispheres  of  his  bi'ain  with  the  corpus  quad- 
rigeminum.  According  as  the  latter  organ  is  relatively  large,  and 
lies  behind  the  hemisi^heres,  uncovered  by  them,  the  animal  is  low 
in  the  scale  of  intelligence  ;  according  as  the  hemispheres  increase 
in  size,  and  so  envelop  and  bury  beneath  them  the  relatively  small 
corpora  quadrigemina,  the  animal  stands  high  in  that  scale.  This 
statement,  however,  scarcely  covers  anything  more  explicit  than 
the  general  fact  that  relative  increase  of  the  cerebral  hemispheres 
is  indicative  of  progressive  mental  life.  Meynert  has  pointed  out 
other  important  relations  between  parts  of  the  brain,  by  which  he 
proposes  to  measure  the  intelligence.  In  the  entire  mass  of  the 
crura  cerebri  we  may  recognize  two  parts,  an  upper  (tegmentum), 
which  stands  in  direct  connection  with  the  optic  thalami  and  the 
corpora  quadrigemina,  and  a  lower  (crusla),  which  is  connected 
through  the  lenticular  nuclei  of  the  striate  bodies  with  the  cere- 
brum. Now  the  greater  the  hemispheres  are  in  comparison  with  the 
corpora  quadrigemina,  the  greater  must  the  mass  of  the  crusta  be  iu 
comparison  with  that  of  the  tegmentum.  The  development  of  the 
pons  Varolii  is  also  essentially  dependent  on  that  of  the  crusta,  for 
the  fibres  of  the  latter  enter  into  the  former  ;  the  arching  of  the 
pons  is  therefore  connected  with  the  development  of  the  hemi- 
spheres. In  general,  then,  the  relative  development  of  the  entire 
tract  represented  by  the  crusta,  or  lower  jDart  of  the  crura  cerebri, 
and  the  nucleus  lenticularis,  the  fibres  of  which  expand  in  the  cere- 
brum, is — according  to  Meynert — a  measure  of  an  animal's  intelli- 
gence. In  man  the  mass  of  the  crusta  on  the  level  of  the  corpora 
quadrigemina  exceeds  that  of  the  tegmentum  ;  in  the  other  mam- 
mals the  reverse  is  true.^ 

§  7.  The  above-mentioned  facts  of  comparative  anatomy,  with 
many  others  similar,  show  plainly  the  unique  significance  which  the 
masses  of  the  brain,  and  especially  the  cerebral  hemispheres,  have, 
as  related  to  the  phenomena  of  self-conscious  mind.  They  may  be 
supplemented  and  confirmed  through  other  facts  furnished  by 
physiology,  esjDecially  of  the  experimental  kind.     Upon  this  point, 

'  Handb.  d.  Physiol,  d.  Meiisclieii,  1844,  I.,  p.  702  f. 
^Sitzgsber.  d.  Wiener  Acad.,  LX.,  iii.  (1869),  pp.  447-462. 
^For  a  brief  but  judicious  discussion  of  this  subject,  see  Briicke,  Vorles' 
ungen  iiber  Physiologie,  1884,  II.,  pp.  52  ff. 


FUNCTIOlSr   OF   CEREBRAL   HEMISPHERES.  249 

for  the  present,  reference  is  simply  made  to  the  results  of  inves- 
tigation as  already  set  forth  in  Part  I.  (see  especially  Chapter 
IV.).  Physiology  demonstrates  that  the  nervous  impulses,  so  far  as 
they  I'esult  in  sensation,  pass  along  centripetal  tracts  which  con- 
verge from  every  portion  of  the  periphery  toward  the  brain  ;  and 
that,  so  far  as  they  x'esult  in  motion  following  upon  idea  and  voli- 
tion, they  pass  along  centrifugal  tracts  diverging  from  the  same 
central  masses.  It  thus  confirms  the  same  theory  which  studies  of 
the  anatomical  structure  of  the  nervous  system  suggest,  namely, 
that  in  these  masses,  and  especially  upon  the  cortex  of  the  cere- 
brum, is  the  common  meeting-place  of  both  kinds  of  impulses.  The 
section  or  injury  of  any  nerve-tract,  even  in  the  spinal  cord,  apart 
from  indirect  and  secondary  influences,  does  not  affect  the  psychical 
functions.  In  such  an  event,  the  parts  of  the  body  lying  j)eriphe- 
rally  from  the  point  of  interruption  are  simjDly  withdi'awn  from  all 
direct  connection  with  sensations  or  volitions.  Sensory  impulses, 
then,  no  longer  occasion  sensations ;  ideas  of  motion  and  volitions 
to  motion,  of  the  parts  thus  disconnected,  become  of  no  effect  in 
producing  the  customary  result.  It  has  also  been  made  obvious 
that,  in  proportion  as  the  masses  of  an  animal's  bi-ain  are  removed 
or  incajDacitated  from  performing  their  functions,  the  evidences  of  a 
varied  and  complex  mental  experience  are  diminished.  The  simple 
spinal  cord  of  a  frog,  acting  as  a  nervous  mechanism,  will  perform 
a  few  wonderful  feats  ;  joined  with  the  medulla  oblongata,  optic 
lobes,  and  other  lower  parts  of  the  brain,  it  will  give  largely  in- 
creased signs  of  psychical  phenomena ;  it  would  not  be  claimed, 
however,  that  the  cerebral  hemispheres  of  this  animal — relatively 
insignificant  as  they  are  when  compared  with  those  of  the  higher 
animals — are  of  no  special  importance  for  its  highest  psychical  life. 
Essentially  the  same  thing,  though  in  more  emphatic  form,  is  true 
of  all  animals  of  a  higher  grade  of  intelligence. 

§  8.  In  the  case  of  man,  the  cerebral  hemispheres  are,  aj^par- 
ently,  the  only  portions  of  the  nervous  system,  between  the  size, 
condition,  and  molecular  activity  of  which  and  the  phenomena  of 
consciousness  there  is  a  direct  correlation.  If,  then,  we  are  to  speak 
of  mental  activities  as  "  localized  "  at  all,  the  locality  must  be  in 
the  cortex  of  the  cerebrum.  The  position  that,  in  the  case  of  man, 
the  spinal  cord  and  all  the  intercranial  organs  below  the  cerebral 
hemispheres,  are  incapable  of  acting  as  the  immediate  physical 
basis  of  mental  states,  is  confirmed  even  by  those  experiments  upon 
other  animals,  which  seem  at  first  sight  to  discredit  it.  The  hypoth- 
esis that  consciousness  has  a  seat  in  the  spinal  cord  of  the  frog  ; 
that,  in  fact,  we  may  properly  speak  of  the  decapitated  animal  as 


250  GENERAL   FUNCTIOlSr   OF  THE   BRAIJST. 

having  a  soul — has  been  urged  by  eminent  j)hysiologists  (Pflnger, 
for  example).  That  the  cord  alone  is  capable  of  various  purpose- 
ful activities,  such  as  serve,  under  certain  circumstances,  as  signs 
of  a  psychical  experience,  may  be  demonstrated  by  experiment 
(comp.  Part  I.,  Chapter  IV.,  §§  4  ff.).  But  unless  one  is  prepared 
to  maintain  that  all  purposeful  activity,  as  resulting  from  excited  ner- 
vous substance,  must  be  correlated  with  phenomena  of  conscious 
sensation  and  volition,  one  can  scarcely  assume  with  confidence 
that  such  phenomena  accompany  the  movements  of  the  decapitated 
frog. 

"What  the  nervous  mechanism  will  do,  when  set  agoing  by  the 
appropriate  stimuli,  depends  not  only  on  its  oi'iginal  structure,  but 
also  on  its  acquired  habits  of  action.  That  this  law  holds  good 
even  for  the  mechanism  of  the  hemispheres  of  the  brain  is  obvious 
from  various  facts.  Stimulating  those  regions  of  the  cerebral  cor- 
tex which  are  connected  with  definite  groups  of  muscles,  in  the  case 
of  the  adult  animal  (for  example,  a  dog),  does  not  call  out  the  same 
responses  in  the  animal  newly  born  (that  is,  under  nine  or  ten  days 
old).  The  case  of  the  bird  which  has  lost  its  cerebral  hemispheres, 
and  which  executes  motions  by  means  of  the  lower  basal  ganglia, 
that  seem  to  indicate  a  complex  psychical  life  (comp.  Part  I., 
Chapter  IV.,  §  20)  is  less  easy  of  solution.  Are  we  to  consider 
such  an  animal  still  capable  of  "sensation,"  "  perception,"  and  "vo- 
lition ?  "  If  this  question  means  whether  any  phenomena  continue 
to  occur  such  as  correspond  to  those  conscious  experiences  of  our 
own  to  which  we  apply  the  above-mentioned  words,  then  we  must 
confess  our  inability  to  answer  it. 

In  general,  we  know  extremely  little  of  the  conscious  mental  life 
of  the  lower  animals.  What  we  conjecture  is  wholly  dependent  on 
the  interpretation,  given  in  terms  of  our  human  consciousness,  to 
motions  of  their  bodies  resembling  those  which  express  definite 
conscious  states  in  ourselves.  But  a  large  part  of  our  own 
bodily  activity  is  ordinarily  not  definitely  correlated  with  any  con- 
scious mental  activity  ;  for  example,  breathing,  winking,  swallow- 
ing, changing  the  posture  of  the  body  in  sleep  and  in  states  of 
jDrofound  meditation,  and  especially  the  very  complex  operations 
involved  in  walking,  singing,  playing  on  musical  instruments,  or 
handling  a  tool,  etc.  In  all  these  and  similar  cases,  we  find  that 
the  intricate  and  purposeful  play  of  the  mechanism  is  by  no  means 
necessarily  connected  with  a  corresponding  series  of  conscious  sen- 
sations and  volitions.  But  in  proportion  as  the  hemispheres  of  an 
animal's  brain  become  relatively  developed,  not  only  their  abso- 
lute but  also  their  relative  significance  is  increased.     The  influence 


LOSS   OF   THE   CEREBRAL   HEMISPHERES.  251 

of  the  brain  proper  upon  the  voluntary  movements  of  an  animal 
is  greatei',  the  higher  the  animal  stands  in  the  scale  of  cerebral 
development  and  of  intelligence.  A  frog,  or  a  fowl,  deprived  of 
its  hemispheres,  can  do  what  is  quite  impossible  for  a  dog  or  an 
ape  in  the  same  condition.  If,  theu,  man's  nervous  mechanism, 
especially  in  case  it  has  been  trained  to  elaborate  co-ordinated  func- 
tions, can,  without  any  corresponding  accompaniment  of  mental 
phenomena,  accomplish  so  much  which  ajppears  significant  of  the 
most  elaborate  psychical  activities ;  a  fortiori,  it  is  likely  that  we 
may  make  this  mechanism,  working  without  consciousness,  account 
for  most  of  what  is  done  by  the  hen  or  pigeon  without  its  cerebral 
hemispheres.  Moreover,  experimental  physiology  undoubtedly 
tends  toward  accounting  more  and  more  fully  for  the  most  com- 
plex bodily  motions  under  the  tei-ms  of  physical  mechanism. 

The  most  marked  result  of  an  animal's  loss  of  the  cerebral 
hemispheres  is  the  sudden  and  great,  or  total  departure  of  its 
intelligence.  This  fact  is,  of  course,  confirmatory  of  the  impres- 
sion that  the  functions  of  these  hemispheres,  and  of  them  alone, 
constitute  the  physical  basis  of  its  intelligence.  We  confess, 
however,  our  inability  to  affirm  that  the  "  psychical  life  "  of  every 
animal  is  inseparably  bound  to  its  continued  possession  of  these 
organs.  There  may  possibly  be  a  varied  psychical  life  of  animals 
that  have  no  brain.  Yet  in  the  case  of  the  higher  mammals,  and 
especially  in  the  case  of  man,  we  need  not  hesitate  to  affirm  the 
probability  of  such  an  inseparable  connection.  The  physical  basis 
of  the  phenomena  of  human  consciousness  is  pre-eminently,  if  not 
exclusively,  the  convoluted  cortex  of  the  cerebrum. 

§  9.  It  is  impossible,  accordingly,  to  avoid  raising  the  inquiry 
whether  some  more  definite  scheme  of  the  localization  of  cerebral 
functions  may  not  be  discovered.  The  cerebral  cortex  is  itself  a 
very  complex  organ,  or  system  of  organs.  Its  different  regions 
are  marked  by  comparatively  slight,  and  yet  not  insignificant,  dif- 
ferences of  structure  ;  they  stand  in  different  local  relations  and 
nervous  connections  with  one  another  and  with  the  ganglia  lying 
below.  This  outlying  rind  of  gray  nervous  matter  is,  of  course, 
not  a  homogeneous  mass.  It  is  made  up  of  innumerable  nervous 
elements  combined  in  various  ways  and  multiform  connections. 
It  may  be  regarded,  then,  as  a  complex  of  organs.  The  question 
therefore  arises  :  Have  the  different  members  of  this  complex  of 
organs  different  relations  to  definite  motor  activities  in  the  pe- 
ripheral regions,  and  to  the  various  phenomena  of  conscious  men- 
tal life  ?  or,  in  other  words  :  Have  different  parts  of  the  cere- 
bral hemispheres  all  the  same  office  and  value  in  relation  to  the  life 


252  EVIDENCE   FOR   LOCALIZATIOlSr. 

of  sensation  and  voluntary  motion  ?  This  is  the  question  generally 
understood  under  the  term — "the  localization  of  cerebral  func- 
tion. " 

§  10.  Most  of  our  definite  knowledge  concerning  the  functions 
of  the  other  parts  of  the  nervous  mechanism  creates  a  presumption 
in  favor  of  some  localization  of  cerebral  functions.  All  the  different 
parts  of  this  mechanism  are,  indeed,  constructed  by  combining 
variously  a  few  elements  of  essentially  the  same  structure  ;  all  of 
them  likewise  are  capable  of  exercising  essentially  the  same  neural 
functions.  But  each  part  of  this  mechanism  has  also  its  special 
functions.  Thus  we  found  that  the  different  nerves  become  classi- 
fied functionally ;  some  are  motor,  voluntary  or  involuntary,  some 
inhibitory,  some  secretory,  some  sensory,  etc.  Hints  of  a  certain 
kind  of  classification  may  be  discovered  for  the  smaller  ganglia  or  col- 
lections of  nerve-cells.  In  making  transverse  sections  of  the  cord, 
different  regions  with  different  functions  appear.  Considered  lon- 
gitudinally, the  cord  is  capable  of  being  more  or  less  definitely 
divided  into  several  so-called  centres,  with  specifically  different 
functions.  Localized  centres,  where  specific  kinds  of  reflex-motor 
activity  have  their  particular  seats,  are  fairly  crowded  together  in 
the  medulla  oblongata.  All  the  lower  parts  of  the  encephalon 
appear  subject,  in  a  measure,  to  the  principle  of  localization.  Shall 
we,  then,  stop  short  in  our  attempts  at  differencing  the  functions  of 
the  locally  separate  parts  of  the  nervous  system  just  at  the  point 
where  we  reach  the  most  complex  and  extended  organ,  or  I'ather 
collection  of  organs,  which  this  system  contains  ? 

§  11.  Notwitlistanding  the  strong  presumption  in  favor  of  the 
localization  of  cerebral  function,  the  beginnings  of  a  successful 
attempt  to  establish  this  theory  are  only  about  fifteen  years  old. 
The  doctrines  of  Gall,  Spurzheim,  and  others  in  the  older  school 
of  phrenologists,  proved  so  inconclusive  as  to  bring  contempt 
ujDon  subsequent  attempts  to  divide  the  hemispheres  of  the  brain 
into  different  functional  areas.  Moreover,  certain  indisputable  facts 
seemed  to  render  impossible  the  assured  beginnings  of  a  theory 
of  cerebral  localization.  Considerable  portions  of  the  human  brain, 
it  was  found,  might  be  lost  without  destroying  any  one  sensory  or 
motor  function.  Moreover,  the  gray  matter  of  the  cerebral  hemi- 
spheres, it  was  then  thought,  could  not  be  directly  excited  by  elec- 
tricity or  by  other  forms  of  stimuli.  The  greatest  experimenters 
in  i)hysiology,  such  as  Longet,  Magendie,  Flourens,  Matteucci,  van 
Deen,  Budge,  and  Schiff,  declared  against  the  localizing  of  cerebral 
function.     In  1842  Longet '  afiS,rmed  that  he  had  experimented  upon 

'  Anatomic  et  physiologie  du  sjsteme  nerveux,  etc.,  Paris,  1842,  i.,  p.  644  f. 


EXPERIMENTS   OF   FRITSCH    A-KD   HITZIG.  253 

the  cortical  substance  of  dogs,  rabbits,  and  kids,  had  irritated  it  me- 
chanically, cauterized  it  with  potash,  nitric  acid,  etc.,  and  had  passed 
galvanic  currents  through  it  in  different  directions,  without  obtaining 
any  sign  whatever  of  resulting  muscular  contraction.  In  the  same 
year  Flourens '  asserted,  on  the  basis  of  numerous  experiments  in 
extirpation,  that  the  lobes  of  the  cerebrum  perform  their  functions 
with  their  whole  mass ;  that  there  is  no  special  seat  for  any  of  the 
cerebral  activities  ;  and  that  even  a  small  remnant  of  the  hemi- 
spheres can  serve  all  the  uses  of  their  collective  functions. 

So  great  was  the  authority  of  the  distinguished  names  just  men- 
tioned, that  their  confident  opinions  gained  general  credence.  The 
evidence  brought  forward  by  Broca  and  others  seemed,  however, 
to  show  some  special  connection  between  a  single  convolution  of 
the  frontal  lobe  and  the  complex  activities  of  articulate  speech ; 
and  the  anatomist,  Meynert,  held  the  opinion  that  the  structure 
and  connections  of  the  cerebrum  show  its  anterior  poi'tion  to  be 
in  general  used  for  motor,  its  posterior  for  sensory  functions.  In 
1867  Eckhard  repeated  the  significant  observation  which  had  been 
made  by  Haller  and  Zinn  more  than  a  century  before  :  namely, 
that,  on  removing  parts  of  the  cortical  substance  of  an  animal's 
brain,  convulsive  movements  occur  in  its  extremities. 

§  12.  It  was  not  until  1870  that  the  "epoch-making"  experi- 
ments of  Fritsch  and  Hitzig "  began  the  modern  era  of  investiga- 
tion into  this  subject.  These  observers  announced  the  fact  that  the 
cerebral  cortex  of  dogs  is,  at  least  in  certain  minute  areas  of  it,  ex- 
citable by  electricity.  They  pointed  out  the  further  fact  that,  while 
some  parts  of  the  convexity  of  the  cerebrum  ai'e  capable  of  motor 
excitation  and  others  not,  the  motor  parts  lie  in  general  to  the 
front,  the  non-motor  to  the  rear  of  this  convexity'.  By  stimulating 
with  an  electrical  current  the  so-called  motor  parts,  co-ordinated 
contractions  of  the  muscles  in  the  opposite  half  of  the  body  are 
obtained.  Of  such  so-called  "motor  centres"  they  indicated,  in 
their  first  announcement,  the  following  five  :  One  for  the  muscles 
of  the  neck,  another  for  the  extension  and  adduction  of  the  fore- 
limb,  another  for  the  bending  and  rotation  of  the  same  limb, 
another  for  the  hind-limb,  and  lastly  one  for  the  face.  From  such 
facts  they  drew  the  conclusion  that  the  principle  announced  by 

'  Recherclies  experimentales  sur  les  proprietes  et  les  fonctions  du  systeme 
nerveux,  etc.,  p.  99  f. 

^See  the  article  by  G.  Fritsch  and  E.  Hitzig  in  the  Archiv  f.  Anat.,  Phy- 
siol., etc.,  1870,  pp.  300-332  ;  and  subsequent  articles  by  Hitzig  in  the  same 
Archiv,  1871,  1873,  1874,  1875,  1876  ;  also  his  work,  Untersuchungeu  iiber 
das  Gehirn,  Berlin,  1874. 


2j4  evidence  for  localization. 

Flourens  is  demonstrably  false.  We  must  rather  admit,  say  they 
that  "  certainly  several  psychical  functions,  and  probably  all,  are 
shown  to  have  their  point  of  entrance  into  matter  or  of  origin  from 
it  at  circumscribed  centres  of  the  cerebral  cortex."  '  The  same 
principle  was  subsequently  defended  at  length  by  Hitzig,  and  the 
number  of  so-called  cerebral  centres  increased.  The  most  note- 
worthy facts  which  these  experimenters  first  made  clear  and  de- 
monstrable have  since  been  verified  by  many  investigators.  Many 
of  these  facts  may,  with  care  and  skill,  be  verified  by  any  observer. 
Dr.  Terrier  in  particular  has  used  the  method  of  Fritsch  and  Hitzig 
to  map  out  the  hemispheres  of  the  brain  of  the  monkey  into  no 
fewer  than  fifteen  kinds  of  centres.  The  testimony  of  human  pa- 
thology, and  the  evidence  of  comparative  anatomy  and  of  histology, 
have  also  been  largely  drawn  upon  either  to  confirm  or  to  confute 
the  conclusions  originally  based  on  experiments  with  animals.  Be- 
fore considering  the  conclusions  themselves,  it  is  necessary  to 
understand  the  true  nature  and  extent  of  the  various  kinds  of  evi- 
dence. 

§  13.  Exner  has  well  said  that  "  a  physiology  of  the  cerebral  cortex, 
in  the  sense  in  which  there  is  a  physiology  of  the  muscle,  etc.,  scarcely 
exists  at  the  present  time."  The  reasons  for  such  a  deficiency  lie 
partly  in  the  very  nature  of  this  organ  and  the  place  it  holds  with- 
in the  animal  economy  ;  as  well  as  partly,  perhaps,  in  certain  prej- 
udices which  have  hindered  the  physical  theory  of  a  material  struct- 
ure so  intimately  related  to  the  action  of  the  mind.  The  cerebral 
cortex  of  the  animals  is  exjDerim  en  tally  approached  only  by  over- 
coming immense  difficulties.  Moreover,  those  physical  and  chemi- 
cal processes  of  the  cerebral  substances,  to  which  we  must  look  for 
any  strictly  scientific  understanding  of  its  physiology,  are  placed 
almost  utterly  beyond  reach  of  investigation.  Seasoning  must  fill 
up  with  conjecture  the  great  gaps  that  lie  between  a  very  complex 
series  of  physical  occurrences,  only  a  part  of  Avhich  are  observable, 
on  the  one  side,  and  on  the  other,  an  equally  complex  group  of 
psychical  occurrences.  The  latter  belong  to  a  different  order  of 
phenomena  from  the  former  ;  and,  moreover,  in  the  case  of  the 
lower  animals — which  must  be  selected  almost  exclusively  for  ex- 
periment—  we  know  nothing  of  these  psychical  occurrences  except 
through  physical  signs  that  are  peculiarly  liable  to  misinterpreta- 
tion. The  result  is  that  our  conclusions  on  the  localization  of  cere- 
bral function  must  be  reached  by  considering  a  great  multitude  of 
complicated  facts,  many  of  which  appear  to  take  sides  with  contend- 

'  Archiv.  f.  Anat,  Physiol.,  etc.,  1870,  p   332. 
*See  Hermanns  Handb   d.  Physiol.,  II.,  ii.,  p.  189. 


STIMULATIOISr   AND   EXTIEPATION.  255 

ing  cliampions  of  dijBferent  theories  who  ahke  appeal  to  them.  It 
is  only  by  observing  the  du'ections  in  which  the  different  Hnes  of 
evidence  seem  to  point  in  common,  that  we  can  reach  even  a  prob- 
able opinion  upon  a  few  points. 

§  14.  Three  great  lines  of  evidence,  leading  from  three  great 
groups  of  facts,  must  be  considered.  These  are  the  evidence  from 
exjDerimentation,  the  evidence  from  pathology,  and  the  evidence 
from  histology  and  comparative  anatomy.  Each  of  the  three  has 
its  peculiar  advantages  and  value  ;  each  also  its  peculiar  difficulties 
and  dangers.  It  is  only  by  regarding  the  combined  testimony  of 
the  three  that  the  highest  probability  at  present  possible  can  be  at- 
tained. 

Experimentation  with  a  view  to  discover  the  localized  functions 
of  the  cerebral  cortex  is  of  two  kinds,  stimulation  and  extirpation. 
Here,  too,  what  has  already  been  said  (Parti.,  chap.  IV.,  §  14)  con- 
cerning the  difficulties  of  the  same  mode  of  investigation  in  the 
sub-cerebral  regions  of  the  encephalon  must  be  recalled  and  made 
more  emphatic.  All  experiment  by  stimulation  of  certain  areas  of 
the  hemispheres  of  the  brain  relies,  of  course,  upon  the  argument 
that  those  areas  whose  stimulation  is  followed  by  tlie  movement  of 
definite  groups  of  muscles  are  especially  connected  with  such  groups 
of  muscles.  The  further  assumption  is  likely  to  be  made  that  these 
areas  constitute  the  special  organs  which  Lave  control,  as  it  were, 
of  the  same  muscles.  Since  it  seems  to  be  a  general  princij)le  that 
the  sensory  and  motor  nerve-tracts  distributed  to  any  region  of  the 
periphery  come  into  tolerably  close  local  relations  to  each  other 
somewhere  within  the  entire  field  of  the  cerebrum,  it  would  seem  to 
follow  that  some  special  connection  exists  between  certain  classes 
of  sensations  and  volitions  and  the  circumscribed  areas  of  cortical 
substance  pointed  out  by  experiment.  It  should  not  be  forgotten, 
however,  that  the  excitation  of  any  group  of  muscles,  by  applying 
stimulus  to  some  area  of  the  cerebral  cortex,  proves  only  that  this 
area  is  somehow  connected  with  such  group  of  muscles.  It  still 
remains  to  be  shown  that  sensory  impulses,  on  arriving  from  such  a 
peripheral  portion  of  the  body,  serve  as  the  physical  basis  for  the 
psychical  phenomena  of  sensation  solely  within  this  circumscribed 
central  area  ;  or  that  conscious  volitions,  in  order  to  be  followed 
by  motion  in  this  peripheral  portion,  must  give  rise  to  the  mole- 
cular commotion  of  the  same  area. 

§  15.  By  far  the  most  efficient  and  manageable  stimulus  for  ex- 
perimenting upon  the  localization  of  cerebral  function  is  the  electrical 
current.  Mechanical  or  chemical  irritation  may,  however,  be  em- 
ployed in  certain  cases.     The  use  of  the  electrical  current  incurs, 


256  EVIDENCE   FOR  LOCALIZATION. 

of  course,  tlie  danger  of  its  diffusion.  Important  objections,  based 
upon  this  fact  and  upon  other  grounds  connected  with  the  use  of 
electricity,  have  been  raised  to  the  conclusions  of  Hitzig.'  To 
Hitzig's  claim  that  the  electrical  currents  which  excite  the  so-called 
motor  areas  are  "very  weak,"  and  therefore  unable,  at  a  very  slight 
distance  from  the  place  of  the  application  of  the  electrodes,  to  affect 
the  nervous  substance,  Hermann  replies  that,  on  the  contrary,  con- 
sidering the  effect  antecedently  to  be  expected,  these  currents  are 
"  surprisingly  strong,"  and  that  the  brain,  in  diffusing  the  currents, 
must  act  like  any  other  substance  {e.g.,  a  mass  of  copper)  of  similar 
form — that  is  to  say,  the  distribution  of  such  a  cuiTent  in  the  sub- 
stance of  the  brain  is  a  purely  geometrical  function  of  the  form  of 
this  substance  and  of  the  position  of  the  electrodes.  Moreover,  it 
is  found  that  increasing  the  strength  of  the  current  ajDplied  to  a 
so-called  "motor  area"  invariably  increases  the  size  of  the  cortical 
region  thrown  into  activity.  That  extra-polar  conduction  actually 
takes  place  in  the  substance  of  the  brain  has  been  shown  by  Dupuy, 
and  by  Carville  and  Duret ;  contraction  of  the  muscle  of  the  rheo- 
scopic  frog  and  deflection  of  the  needle  of  the  galvanometer,  at  re- 
mote distances  from  the  electrodes,  prove  that  the  current  passes 
along  the  whole  extent  of  the  cerebral  hemisphere.  The  excitability 
of  the  cortical  substance  continues  for  hours  after  its  exposure  to  the 
air,  or  after  acids  have  completely  destroyed  its  external  third  por- 
tion. If  the  cortical  area  be  separated  by  a  circular  cut  from  all 
connection  with  the  nervous  substance  below,  it  is  still  excitable  with 
only  a  slight  increase  in  the  strength  of  the  stimulus  applied.  Or 
if  the  gray  substance  of  the  surface  be  wholly  removed,  and  the 
electrodes  plunged  in  the  blood  of  the  cavity  of  one  of  these  so- 
called  motor  areas,  the  customary  results  follow.  Still  further,  the 
size  of  the  circle  within  which  the  minimum  amount  of  stimulus, 
when  applied  to  certain  gyri,  will  serve  to  excite  the  hind-limb  of 
the  animal,  remains  about  the  same  whether  the  amount  of  cortical 
surface  contained  in  the  circle  be  largely  increased  by  a  sulcus 
crossing  it,  or  not. 

From  facts  like  the  foregoing  it  is  argued  that,  while  beyond 
question  the  application  of  a  given  amount  of  stimulus  to  certain 
gyri  of  the  cortical  surface  will  produce  definite  motor  results,  we 
cannot  ajBSrm  those  gyri  to  be  the  true  cortical  centres  of  such 
motion.  Such  gyri  have  accordingly  been  regarded  by  some  as 
merely  connected  with  the  excitation  of  motion  in  a  mechanical 

1  See  especially  the  article  of  Hermann  describing  investigations  under- 
taken by  him  in  company  with  von  Borosnyai,  Luchsinger,  and  others, 
Pfluger's  Archiv  (1875),  x.,  pp.  77  fE. 


EFFECTS    OF   ELECTRICAL    STIMULATION.  257 

way,  through  their  service  in  conducting  the  electrical  stimulus  to 
other  regions  of  the  brain,  especially  to  the  basal  ganglia.  The 
ai'gument  for  the  theory  of  localization  would  need  to  show,  how- 
ever, that  the  electrical  current  stimulates  these  areas  immediately 
to  the  exercise  of  their  central  nervous  functions,  and  does  not 
simply  pass  through  them  to  excite  other  nervous  matter  lying 
beneath. 

To  the  foregoing  objections  the  advocates  of  the  theory  of  locali- 
zation make  the  following  among  other  replies  :  "  The  effect  of  irri- 
tation of  the  basal  ganglia  is  capable  of  exact  estimation  ; "  '  and 
definite  localized  contraction  of  single  groups  of  muscles,  such  as 
comes  from  stimulating  certain  areas  of  the  cortical  surface,  does 
not  follow  from  irritating  the  basal  ganglia.  Stimulation  of  other 
areas  of  the  cortical  surface  which  lie  nearer  to  the  basal  ganglia — 
for  example,  of  the  island  of  Reil,  which  immediately  overlies  the 
corpus  striatum — causes  no  movements.  On  the  contrary,  it  was 
found  by  Carville  and  Duret  that  the  phenomena  evoked  by  stimu- 
lating the  motor  areas  persist,  even  after  the  destruction  of  the 
corpus  striatum.  Moreover,  when  the  animal  is  deeply  etherized, 
the  excitability  of  the  cortical  regions  is  partially  or  wholly  lost.^ 
Since  the  physical  conductivity  of  the  gray  nervous  substance  is 
not  impaired  by  the  anaesthesia,  the  loss  of  function  must  be  due 
to  the  functional  condition  of  this  substance.  More  conclusive  do 
the  facts  appear  to  be,  which  show  that  the  nature  of  the  motor 
reaction  following  upon  the  application  of  stimulus  to  the  cortical 
substance  is  peculiar.  Many  observers  have  found  that  a  stronger 
stimulation  is  necessary  to  bring  about  the  same  motor  results 
after  the  cortical  surface  is  removed  ;  this  is  what  we  should  expect 
on  the  theory  of  localization,  but  the  reverse  of  what  would  be 
true  if  the  effect  of  the  current  was  transmitted  unchanofed  through 
this  surface.  Then,  too,  Franck  and  Pitres'  have  shown  that  the 
effect  of  the  electrical  current  is  retarded  in  the  gray  matter ;  the 
difference  of  time,  as  dependent  upon  whether  the  stimulus  is 
applied  to  the  gray  matter  or  to  the  white  lying  beneath,  being 
about  0.015  second.  This  interval  must  be  spent  in  evolving, 
under  the  influence  of  the  stimulus,  the  distinct  neural  function 
which  belongs  to  the  gray  matter.  Finally,  the  excitation  is  appar- 
ently reinforced  in  strength  by  the  functional  activity  of  the  cor- 
tical substance,  since — as  we  have  just  seen — a  stronger  stimulation 
is  needed  to  produce  the  same  result  after  this  substance  is  re- 

1  Ferrier,  The  Functions  of  the  Brain,  London,  1876,  p.  133  f. 

2  See  Hitzig  in  Archiv  f.  Anat.,  PliysioL,  etc.,  1873,  p.  403. 
2  Archives  de  physiologie,  1875. 


2oS  EVIDElSrCE   FOR   LOCALIZATIOX. 

moved  ;  such  reinforcement  is  the  peculiar  property  of  the  central 
organs. 

It  seems  obvious,  therefore,  that  experiments  with  electrical 
stimulation  of  the  cortical  surface  demonstrate  a  special  connection 
between  certain  more  or  less  definitely  circumscribed  areas  of 
that  surface  and  definite  groups  of  muscles  ;  they  also  create  a 
strong  jDresumption  that  this  connection  is  not  merely  anatomical 
or  structural,  but  also  functional. 

§  16.  The  second  kind  of  direct  experimental  evidence  is  de- 
rived from  observing  the  effects  of  extirjoation.  It  is  natural  to 
arsrue  that  those  areas  of  the  brain,  the  loss  of  which  is  followed 
by  the  loss  or  disturbance  of  motion  in  definite  groups  of  muscles, 
or  by  the  loss  or  disturbance  of  any  class  of  sensory  impressions, 
are  functionally  related  in  a  peculiar  way  to  such  muscles  or  organs 
of  sense.  But  the  application  of  this  argument  is  encompassed 
with  many  difficulties.  In  the  first  place,  it  is  impossible  at 
each  stage  of  the  experiment — which  often  includes  several  days 
or  months  of  observation — to  know  precisely  what  the  condition 
of  the  brain  is.  Post-mortem  examination  of  the  brain  reveals  only 
what  was  the  final  effect  of  the  experiment  in  destroying  its 
tissues.  The  rise  and  fall  of  local  or  extensive  inflammations,  the 
progress  of  degeneration  in  the  nerve-tracts  and  of  abscesses  result- 
ing from  the  primary  lesions,  etc.,  cannot  be  followed  by  the  ex- 
perimenter in  detail.  Nor  can  he  directly  observe  the  formation 
and  education  of  the  tissue  as  it  is  called  upon  for  an  increase  in 
the  amount  of  its  former  functions,  or  perhaps  for  the  discharge  of 
functions  partially  new.  As  a  rule,  then,  it  is  found  that  the 
effects  of  extirpation  change  from  time  to  time  ;  some  of  them  are 
of  first  importance  and  cannot  well  be  overlooked,  and  others  are 
so  delicate  and  minute  as  almost  wholly  to  escape  observation  ; 
some  speedily  pass  away,  others  more  slowly,  still  others  perhaps 
not  at  all.  The  difficulties  are,  of  course,  especially  great  when 
we  try  to  deal  with  effects  upon  the  animal's  sensory  apparatus  and 
his  psychical  world  of  sensations  and  perceptions.  To  tell  whether 
an  animal  sees,  hears,  feels,  smells,  and  tastes,  or  not ;  and  to  tell 
precisely  in  what  sense  it  exercises  these  functions — whether,  for 
example,  its  deficiency  is  "  soul-blindness "  in  any  of  its  various 
degrees — are  not  tasks  which  it  is  easy  to  perform,  or  about  the 
coiTCct  pei'formance  of  which  one  can  indulge  in  a  boundless 
confidence. 

The  demonstrative  value  of  both  kinds  of  experimental  evidence 
— electrization  and  extirpation — is  much  lessened  by  the  fact  that 
it  is  almost  wholly  derived  fx'om  the  lower  animals.     Ethical  con- 


FACTS    OF   HXJMAI^  PATHOLOGY.  259 

siderations,  which  few  investigators  dare  even  occasionally  to  dis- 
regard, forbid  that  the  living  human  brain  should  be  made  the 
subject  of  similar  experiment.  In  ordei',  then,  to  draw  any  safe 
conclusions  from  this  evidence,  it  is  necessary  not  only  that  the 
application  of  the  principle  of  localization  in  general  should  be  as- 
sumed, but  also  that  some  right  should  be  gained  to  transfer  to 
the  human  brain  from  the  map  of  the  cortical  surface  of  the  ani- 
mal's brain,  the  so-called  motor  and  sensory  areas  which  have  been 
determined  by  experiment.  But  it  is  not  even  in  all  cases  clear, 
jDrecisely  what  convolutions  or  parts  of  convolutions  of  the  human 
cerebrum  correspond  to  those  previously  marked  out  on  the  brain 
of  the  animal.  Moreover,  in  the  effort  to  make  any  such  transfer- 
ence of  the  argument  from  the  animals  to  man,  we  meet  again  with 
the  insuperable  difficulty  of  forming  a  correct  mental  picture  of 
the  psychical  life  of  the  animals. 

§  17.  The  evidence  from  human  pathology  for  the  localization  of 
cerebral  function  has  a  peculiar  value  ;  but  it  has  also  its  peculiar 
puzzles  and  dangers.  Such  evidence  is  free,  indeed,  from  the  ob- 
jections which  arise  against  all  attempts  to  carry  the  argument  over 
from  the  cerebral  hemispheres  of  the  lower  animals  directly  to 
those  of  man.  Nature  and  human  intercourse  are  less  kind  to  this 
wonderful  mass  of  nerve-cells  and  nerve-fibres  than  the  electrodes 
and  knife  of  the  physiologist  are  compelled  to  be.  Accident  and 
disease  destroy,  either  suddenly  or  progressively,  the  different 
areas  of  the  cortical  substance  of  the  human  brain.  They  have,  in 
various  cases,  made  such  a  variety  of  attacks  upon  it  as  to  cover  all 
the  areas  of  both  hemispheres.  If,  then,  we  had  a  large  collection 
of  cases  in  which  the  lesions  were  definitely  circumscribed,  or  the 
progress  made  by  the  destruction  of  tissue  Avas  accurately  recorded 
for  every  stage  ;  and  if  we  had  also  a  correspondingly  definite  and 
accurate  description  of  the  motor  and  sensory  disturbances  occa- 
sioned by  these  lesions,  we  might  perhaps  be  able  to  make  a  toler- 
ably conclusive  induction.  But  losses  of  brain-tissue,  when  caused 
by  accident  and  disease,  have  not  the  same  circumscribed  limits 
which  can  be  observed  by  the  knife  or  corroding  acid  of  the  physi- 
ologist. Lesions  of  the  cortical  areas  entirely  free  from  complica- 
tion with  lesions  in  the  sensory  and  motor  tracts  below  are  compar- 
atively infrequent.  Cases  of  total  destruction  of  any  so-called  "area  " 
on  both  hemispheres,  and  of  such  area  alone,  rarely  or  never  occur. 

Furthermore,  it  is  only  by  careful  post-mortem  examination  that 
the  precise  extent  of  the  pathological  changes  can  be  known  ;  this 
examination,  at  best,  reveals  simply  the  last  state  of  the  case. 
The  reports  oi  post-mortem  examinations  are  also,  as  a  rule,  lacking 


260  EVIDElSrCE   FOR  LOCALIZATION. 

,  in  precision.  On  the  other  hand,  the  symptoms  of  motor  or  sensory 
disturbance  are  rarely  described,  from  beginning  to  end,  with  suffi- 
cient accuracy  of  detail  to  be  of  great  service.  Many  large  losses 
of  cerebral  substance  are  followed  by  no  sensory  or  motor  disturb- 
ances which  can  be  distinctly  traced.  In  large  numbers  of  cases 
where  such  disturbances  arise,  they  in  time  pass  almost  or  quite 
wholly  away.  For  these  and  other  reasons  the  best  evidence  at- 
tainable from  pathological  cases,  when  collected  and  sifted,  appears 
surprisingly  confusing  and  self-contradictory.  Pathology  has,  there- 
fore, furnished  the  common  fund  of  cases  from  which  the  most  di- 
verse and  even  contradictory  theories  have  drawn  at  sight  their  stock 
of  so-called  proof.  It  has  been  used  as  the  careless  and  false  witness 
upon  which  either  party,  and  all  parties  to  the  suit,  could  call  for 
precisely  the  testimony  desired.  An  increase  of  information  and 
care  on  the  part  of  those  who  have  opportunity  for  ante-  and  post- 
mortem observation  of  such  cases  will  doubtless,  in  time,  cause 
pathology  to  yield  much  more  assured  results. 

§  18.  The  third  kind  of  evidence  to  which  the  principle  of  the 
localization  of  cerebral  function  may  appeal  comes  from  compara- 
tive anatomy  and  histology.  Comparative  anatomy,  however,  gives 
us  evidence  of  only  the  most  genei'al  kind.  Combined  with  exper- 
iment by  electrical  excitation,  it  shows  that,  on  the  whole,  the 
higher  the  structure  and  intelligence  of  the  animal,  the  more  nu- 
merous and  moi'e  definitely  marked  are  the  "  excito-motor  areas  " 
which  may  be  discovered  on  the  hemispheres  of  its  brain.  Only 
traces,  as  it  were,  of  such  areas  can  be  found  upon  the  cerebral 
hemispheres  of  the  frog  or  the  pigeon  ;  only  a  few  areas  can  be 
doubtfully  pointed  out  for  the  i-at  or  guinea-pig.  The  indications 
are  clearer  and  more  numerous  of  localized  cerebral  function  in 
definite  centres  of  the  brains  of  the  rabbit  and  the  sheep.  But  it 
is  in  dealing  with  the  cerebral  convolutions  of  the  more  highly 
specialized  brains  of  the  dog,  and  particularly  of  the  monkey  or  the 
man-like  ape,  that  the  proofs  of  the  theory  become  most  abundant. 
While,  then,  the  argument  from  all  the  other  animals  to  man  is 
uncertain  and  should  be  used  only  with  great  caution,  the  general 
drift  of  comparative  anatomy  encourages  us  to  place  the  greater 
confidence  in  it,  the  more  nearly  the  bi-ain  of  the  particular  animal 
from  whose  case  we  wish  to  draw  the  inference  resembles  the 
brain  of  man.  At  the  same  time,  the  rash  confidence  with  which 
the  brain  of  the  monkey  has  been  mapped  out  in  detail,  and  human 
pathology  thereupon  ransacked  with  the  purpose  of  finding  some 
warrant  for  copying  this  map  upon  the  brain  of  the  human  species, 
cannot  be  too  carefully  avoided. 


THE  EVIDENCE   OF   HISTOLOGY.  261 

Histology  supplements  and  confirms  the  other  evidence  by  show- 
ing that  the  structure  and  connections  of  different  parts  of  the 
cerebrum  are  such  as  we  should  expect  them  to  be,  in  case  the 
functions  of  the  parts  were  such  as  experimentation  and  pathology 
seem  to  have  discovered.  The  modern  arts  of  microscopy  and 
photography  have  made  possible  an  increasingly  accurate  knowledge 
of  the  intimate  structure  of  the  brain.  Many  great  difficulties, 
however,  still  remain  in  the  way  of  such  perfection  of  this  knowl- 
edge as  will  make  it  available  as  a  secure  foundation  for  a  theory 
of  the  localization  of  cerebral  function.  At  present  the  histology 
of  the  human  cerebral  hemispheres  is  not  in  a  condition  to  take 
the  place  of  a  leader  of  physiological  experiment  and  pathological 
observations.  Its  office  is  still  rather  that  of  rendering  supple- 
mentary evidence  in  correction  or  confirmation  of  the  evidence 
from  the  other  two  sources.  Thus,  for  example,  if  Gliky's  belief 
that  he  traced  the  nerve-tracts  from  the  so-called  motor  centres  of 
the  cerebral  hemispheres  as  they  bend  around  the  striate  bodies 
and  run  into  the  crusta  of  the  crura  cerebri  should  be  demon- 
strated, this  fact  would  constitute  an  item  of  confirmatory  evidence 
furnished  by  histology  to  experimental  physiology  and  pathology, 
in  favor  of  their  general  theory. 

§  19.  According  to  the  foregoing  view  of  the  nature  of  the  three 
kinds  of  evidence  available,  it  would  seem  that,  in  collating  and 
estimating  the  combined  proofs  from  them  all,  the  following  course 
of  inquiry  should  be  pursued.  The  indications  of  experiment  upon 
the  cerebral  hemispheres  of  the  animals— especially  of  those  most 
closely  allied  to  man  in  their  cerebral  structure — by  the  two 
methods  of  stimulation  and  extirpation,  must  first  be  gathered  and 
carefully  weighed.  Only  those  conclusions  upon  which  the  two 
methods  are  found  to  yield  substantially  the  same  results  should  be 
selected  for  further  testing.  The  instances  of  localization  of  cere- 
bral function  thus  detected  in  the  other  higher  mammals  must 
then  be  allowed  to  suggest  to  pathology  the  questions  it  should 
undertake  to  answer  with  reference  to  man.  In  other  words,  ex- 
perimentation with  the  other  animals  suggests  and  strengthens  the 
hypothesis  which  human  pathology  must  try  to  satisfy.  But  in 
undertaking  to  test  such  hypothesis,  pathology  must  be  both  fair 
and  comprehensive  in  its  observations.  All  the  accessible  patho- 
logical cases  must  be  sifted  and  those  only  selected  to  bring  for- 
ward as  evidence  which  have  the  definite  nature,  and  have  received 
the  careful  examination  recorded  in  detail,  that  are  necessary  to 
make  them  of  real  value.  The  corrective  or  confirmatoiy  evidence 
of  histology  must  then,  so  far  as  possible,  be  summoned  to  aid  in 


262  EVIDENCE   FOU   LOCALIZATION. 

forming  our  final  conclusions.  It  is  not  until  all  the  kinds  of  proof 
unite  with  a  large  and  substantial  agreement,  if  not  with  an  abso- 
lute uniformity,  that  we  can  feel  the  utmost  confidence  attainable 
in  our  results.  If  it  be  found  that  certain  regions  of  the  cerebral 
hemispheres  of  the  higher  animals  are  the  only  ones  to  respond 
when  stimulated  with  movements  in  definite  peripheral  parts  of  the 
body,  and  that  the  injury  of  those  same  central  regions  alone,  or 
chiefly,  causes  motor  and  sensory  disturbances  in  the  same  periph- 
eral parts  ;  if  it  also  be  found  that  lesions  of  the  corresponding- 
regions  of  the  human  brain  are  alone,  or  chiefly,  followed  by  similar 
motor  and  sensory  disturbances,  and  that  lesions  of  other  regions 
alone  are  rarely  or  never  followed  by  these  same  disturbances  ;  and, 
finally,  if  it  be  found  that  these  same  cortical  regions  have  in  the 
human  body  a  special  anatomical  connection  with  these  same  pe- 
ripheral parts  ;  then  we  have  reached  the  most  conclusive  evidence 
attainable  for  a  theory  that  the  cerebral  functions  are  localized  in 
the  case  of  man.  But  precisely  what  is  meant  by  such  "  localiza- 
tion "  may  still  remain  more  or  less  a  matter  of  dispute.  We  con- 
sider now  a  summary  of  the  evidence  according  to  the  foregoing 
principles. 


CIIAPTEE  II. 

THE  LOCALIZATION  OF  CEEEBEAL  FUNCTION.     [Continueb.] 

§  1.  On  attempting  to  make  an  induction  from  all  the  three  kinds 
of  evidence  which  may  be  adduced  in  answer  to  the  question, 
whether  the  different  functions  of  the  cerebral  cortex  have  special 
relations  to  its  different  localities,  no  other  difficulties  are  on  the 
whole  so  great  as  those  which  come  from  so-called  "negative  cases." 
These  negative  cases  force  the  inquirer  to  undertake  a  detailed  ex- 
perimental and  pathological  examination.  "  That  the  cortex  of  the 
cerebrum,  the  undoubted  material  substratum  of  our  mental  opera- 
tions," says  Ecker,'  "is  not  a  single  organ,  which  is  brought  into 
play  as  a  whole  in  the  exercise  of  each  and  every  psychical  function, 
but  consists  rather  of  a  multitude  of  mental  organs,  each  of  which 
is  subservient  to  certain  intellectual  processes,  is  a  conviction  which 
forces  itself  upon  us  almost  with  the  necessity  of  a  claim  of  reason." 
But  even  the  proposition  that  the  brain  is  the  "material  substratum 
of  our  mental  operations,"  is  very  far  indeed  from  having  the  char- 
acter of  a  rational  necessity.  The  further  proposition  that  the  cor- 
tex of  the  cerebrum  "  consists  of  a  multitude  of  mental  organs,"  is 
an  inadequate  statement  of  a  conclusion  which,  at  the  very  best, 
we  can  adopt  only  as  the  result  of  a  long  series  of  complex  and  con- 
flicting researches.  Li  fact,  considerable  areas  of  the  cortical  sur- 
face appear,  at  first,  not  to  have  any  immediate  relation  to  any  psy- 
chical function  whatever. 

The  first  general  principle  to  be  admitted  in  all  attempts  at  a 
theory  of  the  localization  of  cerebral  function  is,  then,  of  a  nega- 
tive character.  This  principle  is  based  upon  the  negative  results 
of  physiological  inquiry.  Considerable  areas  of  the  cortical  sur- 
face do  not  respond  with  motor  activities  when  stimulated.  Con- 
siderable portions  of  the  cortical  substance  may  be  extirpated  or 
lost  by  disease  without  the  destruction  or  appreciable  disturbance 
of  any  motor,  sensory,  or  more  purely  intellectual  functions.  To 
such  an  astonishing  extent  is  this  true  as  to  throw  temporary  doubt 
not  only  over  the  whole  theory  of  the  localization  of  cerebral  func- 
■  The  Convolutions  of  the  Human  Brain,  p.  1.     London,  1873. 


264  STIMULATION   AND   EXTIRPATION. 

tion,  but  even  over  tlie  statement  that  the  cerebral  cortex,  as  a  whole, 
is  the  only  "  material  substratum  "  of  mental  operations. 

§  2.  Attention  has  already  been  called  (Chap.  L,  §  11)  to  the  fact 
that  Longet,  Flourens,  and  other  great  physiologists,  considered 
the  cerebral  hemispheres  to  be  active  as  a  whole  in  all  their  func- 
tions, and  this,  partly,  because  they  found  them  not  irritable  by  the 
electi'ical  current.  The  discovery  of  Fritsch  and  Hitzig  in  1870  de- 
monstrated that  a  part  of  the  hemispheres  of  the  dog,  and  a  part 
only,  gives  signs  of  being  excited  by  the  application  of  stimulus. 
This  part  they  called  "  motor,"  and  located,  in  general,  in  the  fore 
part  of  the  hemispheres  ;  behind  lay  the  region  called  "  non-mo- 
tor," because  it  gave  no  response  on  being  stimulated.'  Even  with- 
in this  so-called  "motor"  region  the  early  reseai'ches  of  these  in- 
vestigators pointed  out  only  five  spots  of  a  small  fraction  of  an  inch 
in  diameter  (the  electrodes  were,  as  a  rule,  separated  not  more  than 
2-3  mm.)  that  could  be  more  definitely  related  to  the  movement  of 
certain  groups  of  muscles  ;  between  and  around  these  spots  lay  the 
much  larger  areas  of  negative  resrdt.  Subsequent  experiments 
added  a  few  more  such  irritable  areas  to  the  map  of  the  cerebral 
hemispheres  of  the  dog.  A  large  number  of  so-called  centres,  cover- 
ing an  increased  amount  of  the  cortical  surface,  have  been  pointed 
out  by  Ferrier  and  others  on  the  cerebral  hemispheres  of  the  mon- 
key. Fully  half  of  this  number,  however,  cannot  be  regarded  as 
having  anything  like  a  demonstrable  character  ;  and  much  fault  has 
justly  been  found  ^  with  many  operators  upon  the  brains  both  of 
monkeys  and  of  dogs,  for  their  lack  of  precision  in  experiment,  and 
haste  in  drawing  conclusions. 

Experiments  in  extirpation  also  show  that  considerable  areas 
of  the  cortical  substance  may  be  removed  without  perceptibly  im- 
paiiing  any  of  the  motor  or  sensory  functions  of  the  animal.  In- 
deed, even  when  the  loss  of  the  cortical  substance,  thus  artificially 
produced,  extends  over  almost  an  entire  hemisphere,  or  over  a  large 
portion  of  both  hemispheres,  the  operation  may  not  result  (in  the 
case  of  the  dog,  ordinarily  does  not  result),  in  the  pervmnent  and 
complete  loss  of  any  siDecific  function,  motor  or  sensory.  So  true  is 
this  that  one  eminent  observer,  Goltz,  has  maintained,  on  the  basis 

'  Archiv  f.  Anat.,  Physiol.,  etc.,  1870,  p.  311. 

^  See,  for  example,  Munk  s  strictures  of  Ferrier,  Ueber  d.  Functionen  d. 
Grosshirnrinde,  Berlin,  1881.  pp.  14  fE.  (also  p.  G  f.  ;  36  f. — "  roh  w<ir  operirt, 
roh  beohachtet,  roh  geschlossen '''').  On  the  other  hand,  the  charge  of  careless- 
ness in  experiment,  and  of  illogical  conclusions  is  freely  made  against  Munk 
himself,  both  by  advocates  of  rival  theories  of  localization,  like  Dr.  Yeo  and 
others,  and  also  by  opponents  of  all  theories  of  localization,  like  Goltz,  Lob, 
and  others. 


EVIDENCE   FROM   NEGATIVE   CASES.  265 

of  many  experiments  in  extirpation,  that  it  is  chiefly  the  quantity  of 
the  cerebral  substance  destroyed,  in  large  measure  irrespective  of 
the  locality,  which  determines  the  nature  and  extent  of  the  result- 
ing psychical  disturbances.  The  arguments  of  Goltz  (as  he  him- 
self admits)  do  not  answer  those  urged  for  a  certain  kind  and  de- 
gTee  of  the  localization  of  cerebral  function.  But  his  experiments 
furnish  a  large  number  of  facts  which  emphasize' the  negative  char- 
acter of  many  of  the  results  of  experiment.  This  fact  is  in  itself 
undeniably  unfavorable  to  any  theory  which  would  map  out  the  en- 
tire cortical  surface  into  so-called  centres  or  areas,  to  be  considered 
as  separate  organs  of  particular  psychical  processes. 

§  3.  The  negative  evidence  from  certain  cases  in  human  pa- 
thology is  yet  more  astonishing  and  perplexing.  At  first  sight  it 
seems  to  suggest  the  conclusion  that  the  mind  can  dispense,  with- 
out impairment,  with  a  considerable  mass  of  brain-substance,  no 
matter  from  what  region  it  be  subtracted.  Many  cases  of  large  le- 
sions of  the  cerebral  hemispheres  in  man,  with  no  resulting  disturb- 
ance of  the  psychical  functions,  are  recorded.' 

Berenger  de  Carpi  tells  of  a  young  man  who  had  a  foreign  body 
of  four  fingers'  breadth  square  driven  into  the  substance  of  bis 
brain  until  it  was  buried.  Much  of  this  substance  was  lost  when 
the  foreign  body  was  removed,  and  more  yet  some  thirteen  days 
later.  Nevertheless,  the  patient  lived  for  a  long  time  in  the  enjoy- 
ment of  all  his  faculties. 

Longet  was  acquainted  with  an  army  ofiicer  who  had  lost,  by  a 
wound  in  the  parietal  region,  a  large  quantity  of  brain-substance  ; 
yet  he  remained  mentally  vivacious  and  showed  no  other  result  of 
the  lesion  than  a  tendency  to  grow  tired  easily.  The  same  authority 
communicates  ^  the  case  of  an  Italian  whose  skull  was  crushed  in 
the  right  parietal  region  by  a  stone.  So  much  of  the  substance  of 
the  brain  was  lost  on  the  wound  being  dressed,  and  subsequently 
through  a  fall  from  his  bed  (on  the  eighteenth  day)  and  through 
intoxication  (on  the  thirty-fifth  day),  that  the  attendant  physician 
calculated  the  lesion  must  have  reached  down  nearly  to  the  corpus 
callosum.  The  man,  however,  lived  without  any  apparent  impair- 
ment of  psychical  functions  ;  but  we  note  in  this  case  a  permanent 
laming  of  the  limbs  of  the  left  side. 

'  See  the  list  of  such  cases  in  Ferrier,  the  Localization  of  Cerebral  Disease, 
London,  1878,  pp.  25  ff.;  Hermann,  Handb.  d.  Physiol.,  II.,  ii.,  pp.  333  ff.; 
Briicke,  Vorlesungen  liber  Physiol.,  II.,  p.  57  f.  Wien,  1884;  and  the  works 
cited  by  the  two  former,  especially  Pitres,  Lesions  du  centre  ovale,  Paxis, 
1877. 

^  Recorded,  however,  by  Quesnay. 


2Q6  STIMULATION   AND   EXTIRPATION. 

A  remarkable  case  is  narrated  by  Brticke, "  on  the  authority  ol 
a  certain  Dr.  Kratter.  By  a  blow  from  a  stone  on  the  parietal 
region  of  the  skull,  one  Ivan  Mussuhn  was  thrown  to  the  ground  ; 
but  within  two  hours  he  recovered  so  that  he  himself  went  to 
the  "  praetor  "  and  entered  complaint  against  his  assailant.  For 
twenty  days  he  hved  in  apparently  full  possession  of  his  powers 
of  motion,  sensation,  and  intelligence  ;  on  the  twenty-first  day  he 
suddenly  died.  The  entire  left  cerebral  hemisphere  was  found  on 
examination  to  be  a  disorganized  mass.  It  is  to  be  noticed,  how- 
ever, that  the  autopsy  did  not  take  place  until  some  eighteen  hours 
after  death,  and  that  we  have  no  good  means  of  judging  what  the 
condition  of  the  injured  hemisphere  was  during  the  twenty  days 
preceding  his  sudden  death. 

Remarkable  instances  of  defective  brains  are  also  on  record  ;  for 
example,  the  case  which  Lallemand  nari'ates  of  a  person  of  normal 
psychical  constitution  in  whose  cerebrum  the  entire  place  of  the 
right  hemisphere  was,  after  death,  unexpectedly  found  to  have 
been  filled  with  a  serous  fluid.  Here  again,  however,  there  had 
been  lameness  of  the  left  side  of  the  body  from  birth. 

Extensive  lesions  without  marked  motor  or  sensory  disturbances 
occur  by  far  most  frequently  in  the  frontal  lobes  of  the  cerebral 
hemispheres.  Yet  similar  negative  cases  are  by  no  means  infre- 
quent also  in  the  occipital  and  temporo-sphenoidal  lobes.  Trous- 
seau narrates  the  case  of  an  officer  who  was  shot  through  the  head 
in  the  middle  of  the  frontal  lobes,  and  who  showed  until  death, 
which  occurred  from  inflammation,  no  signs  of.  any  kind  of  paral- 
ysis. The  work  of  M.  Pitres  ^  contains  a  large  collection  of  cases, 
in  which  the  frontal  lobes  have  been  the  seat  of  extensive  disease, 
of  softening,  or  of  abscess,  without  any  symptoms  of  laming  what- 
ever ;  in  most  of  which,  also,  no  disturbance  of  psychical  con- 
dition was  observed.  That  sudden  extensive  lesions  may  occur  in 
this  region  without  inducing  sensory  or  motor  paralysis,  is  shown 
in  a  marked  way  by  the  celebrated  "American  crowbar  case."  ^ 
By  prematui'e  discharge  of  blasting  powder  an  iron  bar,  three  feet 
seven  inches  in  length  and  one  and  one-fourth  inch  in  diameter, 
was  driven  through  the  brain  of  a  young  man.  The  missile  en- 
tered at  the  left  angle  of  the  jaw,  and  passed  through  the  top  of  the 
head  near  the  sagittal  suture  in  the  frontal  region  ;  it  was  picked 
up  at  some  distance  off,  covered  with  blood  and  brains.     The  pa- 

'  Vorlesungen  iiber  Physiol.,  11.,  p.  57. 
'^  Lesions  du  centre  ovale. 

"  See  the  paper  in  the  Am  Journal  for  Med  Sciences,  by  Dr.  Bigelow,  July, 
1850,  and  the  one  read  before  the  Masa.  Med.  So.  by  Dr.  Harlow,  June,  1868, 


GENEKAL   MOTOR   EEGION.  267 

tient,  although,  for  the  moment  stunned,  recovered  in  a  few  min- 
utes so  as  to  ascend  a  flight  of  stairs  and  give  to  the  surgeon  an 
intelhgible  account  of  his  injury.  He  Hved  twelve  and  a  half  years 
afterward,  with  no  noticeable  impairment  of  his  sensory-motor 
powers.  Examination  of  the  skull  showed  that  the  substance  de- 
stroyed by  the  bar  must  have  been  confined  to  the  frontal  region, 
with  the  possible  exception  of  the  tip  of  the  temporo-sphenoidal 
lobe. 

Boyer  narrates  the  case  of  an  epileptic  child,  that  showed,  how- 
ever, no  other  abnormal  nervous  phenomena,  whose  entire  temporal 
lobe  on  the  left  side  was  found  to  have  been  destroyed.  Instances 
of  extensive  lesions  in  the  occipital  lobes,  without  any  resulting 
sensory  or  motor  disturbances,  might  also  be  given. 

§  4.  It  must  be  confessed,  in  the  words  of  Exner,'  that  the 
understanding  of  cases  of  this  sort  "is  made  more  difficult  rather 
than  easier  by  recent  researches."  Nevertheless,  a  large  amount 
of  concurrent  testimony  from  all  three  main  sources  of  evidence 
proves  that  some  theory  may  be  framed  in  acknowledgment  of  a 
more  definite  localization  of  cerebral  function.  Such  theory  can 
be  most  clearly  established  Avith  respect  to  the  cerebral  region 
esj)ecially  concerned  in  the  motor  functions.  This  region  is  the 
one  Ijing  about  the  great  central  fissure,  or  fissure  of  Rolando  ; 
more  precisely  still,  it  embraces  the  gyrus  centralis  anterior,  the 
gyrus  centralis  posterior,  and  the  prolongation  of  the  two  on  the 
median  surface  of  the  brain  in  the  lohulus  paracentralis.  (Comp. 
Figs.  87  and  88).  More  definite  localizations  still,  of  smaller  re- 
gions within  the  larger  one — e.  g.,  for  the  upper  limbs,  for  the  lower 
limbs,  for  the  separate  fingers,  etc. — are  more  doubtful ;  they  can 
by  no  means  appeal  to  the  same  amount  of  evidence  as  that  at  com- 
mand of  the  more  genei-al  induction. 

§  5.  The  evidence  from  experiments  in  stimulation  indicates  that 
we  are  to  look  for  the  so-called  ^^ motor  areas'"  in  the  above-mentioned 
convolutions  about  the  fissure  of  Rolando.  The  original  experi- 
ments of  Fritsch  and  Hitzig  ^  located  the  five  motor  areas  as  fol- 
lows :  The  centre  for  the  muscles  of  the  neck  (marked  A  in  the 
figure)  in  the  middle  of  the  pree-frontal  gyrus  at  the  spot  where  its 
surface  falls  off  steep  ;  the  centre  for  the  extensor  and  adductor  of 
the  fore-limb,  at  the  outermost  end  of  the  post-frontal  gj^rus  in  the 
region  near  the  end  of  the  frontal  fissure  (-1^  in  the  figure) ;  the 

^  111  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  834. 

»  See  Archiv  f.  Anat,  Physiol.,  etc.,  1870,  p.  312  f . ;  comp.  Taf.  IX  B.  by 
Hitzig  in  the  same  Archiv  for  1873,  from  which  the  accompanying  figure  is 
taken. 


268 


STIMULATION   AND   EXTIRPATION". 


centre  for  the  bending  and  rotation   of   the   same   limb,  a  little 
farther  back  (+  in  the  figure);  the  centre  for  the  hind-limb,  in 

the  post- frontal  gyrus  but  to- 
ward the  median  line  of  the 
^         hemisphere  and  back  of  the 

*  preceding  two  centres  (4^    iu 
f        the  figure) ;  the  facial  centre, 

#  in   the   middle    part   of   the 
0       gyrus  lying  above  the  fissure 

of  Sylvius (4~0  in  the  figure). 

**       These    experimenters    found 

■^      also  that  the  muscles  of  the 

o      back,  tail,  and  abdomen,  were 

excited     to     contraction     by 

stimulating  points  lying  be- 

'*'    tween  those  marked  as  above  ; 

but  they  could  not  definitely 

circumscribe  the  cortical  areas 

Fig.  83.— Hitzig's  Motor  Areas  on  the  Cortex  of  the     -^Jiich   WCre  to  be  aSSiffUed  tO 
Dog.     The  left  hemisphere  belongs  to  one  animal,  ° 

the  right  to  another;    o,   the  mlmis  cruciatUH,     tlieSC  mUSclcS. 

around  which  the  gyrus  sigmoideus  bends  ;  oooo,  i.       i.i  i,      i. 

area  for  the  face.    The  other  symbols  are  explained  J3y    retercnce    tO    tUe    CUart 

*''  *''^  ^''^-  of  the  numerous  "  centres  of 

electrical  irritation  "  Avhich  Terrier  '  claims  to  have  discovered  on  the 
cerebral  hemispheres  of  the  monkey,  it  will  be  seen  that  they  are  set 
close  together  in  the  two 
central  convolutions 
{gyri  centrales,  called 
by  Ferrier  the  "  ascend- 
ing frontal"  and  "as- 
cending parietal ")  and 
in  the  immediately  ad- 
joining parts  of  the 
frontal  and  temporo- 
sphenoidal  convolu- 
tions. Thus,  the  cen- 
tres (2,  in  part),  (3),  (4, 
in  part),  (5,  in  part), 
(6),  (7),  (8),  (9),  and 
(10),  are  located  in  the 
anterior  central  ("  ascending  frontal ")  convolution  ;  (2,  in  part), 
(4,  in  part),  (11,  in  part),  and  (a),  (b),  (c),  (d),  are  placed  on  the  poste- 
'  See  The  Functions  of  the  Brain,  pp.  141  fE. ,  149  f. ,  and  305  f .  London,  1876, 
In  the  second  edition  (1886),  pp.  240  ff. 


Pig.  84.— Areas  on  the  Left  Hemisphere  of  the  Monkey,  by 
stimulating  which  Ferrier  obtains  motion  in  definite  groups 
of  muscles. 


EFFECT   OF   ELECTRICAL   STIMULUS.  269 

rior  central  ("  ascending  parietal ")  convolution ;  the  centres  (12)  and 
(5,  in  part)  are  situated  on  parts  of  the  superior  and  middle  frontal 
convolutions  adjacent  to  the  anterior  central ;  and  (14)  on  the  su- 
perior temporo-sphenoidal  convolution. 

Further  and  more  recent  information  seems  to  render  the  experi- 
ments in  the  electrization  of  the  cerebral  areas  of  animals  more 
available  for  use  in  confirming  the  general  argument  in  behalf  of 
some  kind  of  localization  of  cerebral  function  in  the  case  of  man. 
Luciani  and  Tamburini,  as  well  as  other  experimenters,  have  agreed 
with  Hitzig  and  Terrier  in  finding  small,  circumscribed  motor  cen- 
tres on  the  cortex  of  the  dog,  monkey,  rabbit,  and  other  animals. 
Some  experimenters  (Bochefontaine  and  Vulpian,  e.g.)  claim  to 
have  discovered  that  the  minute  areas,  at  first  excitable,  after  a 
time  cease  to  be  so  ;  and  that  other  areas,  at  first  not  excitable, 
afterward  become  excitable — that  is,  a  displacement  of  the  excit- 
able points  takes  place. 

More  recently  still,  it  has  apparently  been  discovered  '  that  Ex- 
ner's  view  (to  be  explained  subsequently)  of  the  existence  of  "  ab- 
solute "  and  "  relative  "  motor  fields  in  the  case  of  man  is  probably 
applicable  to  the  animals  also.  Paneth  found  that  a  number  of 
minute  areas  (or  spots)  for  each  one  of  the  several  groups  of  muscles 
could  be  detected  as  lying  in  the  larger  "  excitable  zone  "  of  the 
cortex.  These  areas,  vmlike  the  immediately  surrounding  ones, 
could  be  excited  when  cut  around,  but  not  when  cut  heneMh  ;  the 
fibres  whose  function  it  is  to  bring  a  definite  group  of  muscles  to 
contraction  seem  then  to  proceed  directly  from  these  cortical  spots 
to  the  lower  parts  of  the  brain.  A  number  of  such  belong  to  each 
muscle  excitable  ;  but  only  two  general  "  fields  "  are  distinguish- 
able, within  which  all  the  isolated  motor  spots  are  located ;  one 
field  is  for  the  extremities,  the  other  for  the  orbicularis  palpebrarum. 
The  former  is  situated  in  the  posterior  division  of  the  gijrus  sig- 
moideus.  The  minute  areas  for  the  different  muscles  of  the  ex- 
tremities are  sharply  limited  ;  they  do  not  wholly  cover  each  other  ; 
and  those  for  any  special  muscle  (the  extensor  digitorum  of  the  fore- 
foot, etc.)  are  of  small  extent  in  comparison  with  the  field  or  zone 
which  may  be  looked  on  as  common  to  all  the  extremities.  The 
excitability  of  the  different  muscles  is  not  all  alike  ;  this  Paneth  ex- 
plains by  assuming  that  the  number  of  nerve-elements  assigned  to 
each  is  not  alike. 

§  6.  Experiments  in  extirpation  confirm,  at  least  in  a  general  way, 

'  See  the  art.  of  J.  Panetli,  "Ueber  Lage,  Ausdehnung,  \ind  Bedeutung  der 
absoluten  motorisclieu  Felder,"  etc.,  in  Pfliiger's  Archiv,  xxxvii.  (1«85)  pp. 
530  fE. 


270  STIMLTLATION   AND    EXTIRPATION. 

the  above-mentioned  results  of  experiments  in  stimulation.  The 
destruction  of  the  substance  of  those  cortical  areas  which  respond 
to  the  current  of  electricity  with  the  co-ordinated  movement  of  def- 
inite groups  of  muscles,  causes  a  temporary  or  permanent  impair- 
ment of  the  functions  connected  with  the  same  groups  of  muscles. 
In  their  first  report  Fritsch  and  Hitzig  called  attention  to  certain 
experiments  of  their  own  in  removing  from  the  cerebral  hemispheres 
of  two  dogs  the  nervous  substance  of  the  centre  which  had  already 
been  fixed  upon  by  them  as  that  for  the  "  right  fore  extremity  " 
of  the  animal.  These  experiments  they  found  confirmatory  of  the 
views  derived  from  stimulation.  The  animals  operated  upon, 
when  sitting  or  standing  or  running,  used  the  right  fore-leg  un- 
skilfully ;  this  part  of  the  body,  however,  showed  no  marked  dimi- 
nution of  sensibility  under  hard  pressure.  Other  observers  have 
since  performed  many  similar  experiments  ; — especially  Ferrier  on 
monkeys,  and  Goltz  and  Munli  on  dogs.  Among  them  all  no  oth- 
ers are  so  carefully  refined  as  are  those  of  Munk."  But  the  very 
refinement  of  these  experiments  subjects  them  to  more  of  distrust, 
in  certain  particulars. 

§  7.  The  earlier  experiments  of  Munk  were  confined  to  the  convex 
surfaces  of  the  parietal,  occipital,  and  temporal  lobes  of  dogs  ;  they 
consisted  in  removing  clean-cut  circular  bits  of  the  cerebral  sub- 
stance about  three-fifths  of  an  inch  in  diameter  and  one-twelfth  of  an 
inch  thick — sometimes  simultaneously,  from  the  symmetrical  areas 
of  the  two  hemispheres,  and  sometimes  with  an  interval  between  the 
two  operations.  Munk's  general  conclusion  is  stated  as  follows  : 
If  a  line  be  drawn  from  the  terminal  point  of  the  fissure  of 
Sylvius  vertically  toward  the  falx  cerebri,  it  will  mai'k,  approxi- 
imately,  the  limits  of  two  spheres  that  are  sharply  distinguished 
experimentally — namely,  an  anterior  motor  and  a  posterior  sensory 
sphere."  Extirpations  in  front  of  this  line  always  occasion  dis- 
turbances of  motion,  those  back  of  it  never  so.  More  precisely, 
the  cerebral  convolutions  of  the  dog  may,  according  to  Munk,  be 
mapped  out  into  the  several  spheres  and  regions  indicated  in  the  ac- 
companying figure  (Fig.  85).  It  will  be  noticed  that  three  of  these 
regions  (namely,  C  for  the  hind  leg,  D  for  the  fore  leg,  and  E  for 
the  head)  correspond  pretty  accurately  to  the  centres  of  stimulation 
fixed  upon  by  Fritsch  and  Hitzig.  Extirpations  of  the  cortical  sub- 
stance in  these  i-egions,  of  only  a  few  millimetres  broad  and  not 
more  than  two  deep,  are  regularly  followed  by  definitely  localized 

'  See  his  Gesammelte  Mittheilungen  aus  d.  Jaliren  1877-80,  in  the  book, 
Ueber  d.  Functionen  d.  Grosshiruriude.     Berhu,  1881. 
2  Munk,  ibid.,  p.  11. 


MOTOR   AREAS  '   OF   THE   DOG. 


271 


distiu'bance  of  motion.  For  example,  let  the  region  (Z))  be  removed 
from  the  left  cerebral  hemisphere  of  a  dog.  At  the  end  of  from  three 
to  five  days  and  after  the  fever  from  the  operation  has  subsided, 
abnormal  phenomena  connected  with  the  fore-leg  of  the  opposite 
side  will  be  observed.  If  any  other  limb  of  the  animal  than  the 
right  fore-leg  be  touched  lightly,  the  dog  will  look  quickly  around ; 


Fig.  85.— Areas  on  the  Brain  of  the  Dop.  (According  to  Munt.)  A,  centre  of  the  Bye ;  B,  of 
the  Ear ;  C,  of  the  sensations  of  the  hind  Leg- ;  D,  of  the  fore  Log  ;  E,  of  the  Head ;  F,  of  the 
Apparatus  for  protecting  the  Eye  ;  G,  of  the  Region  of  the  Ear  ;  H,  of  the  Neck :  J,  of  the 
Rump. 


and  if  of  a  bad  temper  will  try  to  bite  the  offending  hand.  He 
will  also  quickly  withdraw  any  other  limb  when  it  is  subjected  to 
even  very  slight  pressure.  But  hard  pressure  and  pinching  or 
sticking  of  the  right  fore-leg  is  either  followed  by  no  result,  or  else 
by  mere  withdrawal  of  the  limb,  as  though  in  reflex  motion,  without 
any  attention  being  paid  to  the  attack.  Moreover,  this  particular 
limb,  unlike  all  the  others,  can  be  put  into  unnatural  and  uncom- 
fortable positions — can  be  bent,  stretched,  set  on  the  ground  with 


272  STIMULATION   AND   EXTIEPATION. 

the  back  of  the  foot  down,  etc. — without  any  resistance  on  the 
animal's  part  or  any  apparent  disposition  to  remove  it  to  the 
normal  and  comfortable  position.  According  to  Munk,  the  animal 
has  apparently  lost  all  mental  picture  of  this  one  limb,  and  there- 
fore all  power  to  move  it  intelligently  and  voluntarily.  If  he  has 
been  accustomed,  on  call,  to  put  the  right  leg  into  his  master's  hand, 
he  will  now  respond  with  the  left  instead  of  the  right  foot  to  the 
same  call.  The  dog  no  longer  handles  his  food  with  the  right 
foot.  In  running  he  slips  on  that  foot.  If  he  is  drawn  to  the 
edge  of  a  table  and  the  right  leg  forcibly  stretched  out  over  it,  he 
will  allow  the  leg  to  hang  down  thus,  although  evidently  aware  of 
the  dangerous  position  in  which  this  places  him.  Such  an  animal 
can,  however,  still  walk  and  run,  using  all  four  limbs.  The  "  gross 
mechanism  "  of  motion — to  borrow  Munk's  phrase  ' — still  acts  as  it 
did  before;  but  the  so-called  "cerebral"  or  intelligent  quality  in 
the  management  of  this  particular  limb  has  been  lost. 

Gradually  the  phenomena  which  indicate  impairment  of  cerebral 
function  as  related  to  the  movement  of  the  foi-e-leg  diminish  in 
magnitude.  Less  pressure  is  then  necessary  to  secure  the  with- 
drawal of  the  injured  limb  ;  the  dog  is  less  surprisingly  unskilful 
in  its  use.  At  the  end  of  four  or  five  weeks  the  moi-e  marked 
symptoms  of  his  loss  of  function  have  probably  disappeared  ;  at  the 
end  of  eight  or  ten  weeks  it  may  be  difficult  or  impossible  to  dis- 
tinguish his  movements  from  those  of  a  perfectly  sound  animal. 
If,  however,  the  size  of  the  pieces  of  cerebral  substance  taken  from 
any  of  the  so-called  "  motor  regions  "  be  somewhat  larger  than  that 
indicated  above,  recovery  is  slower  and  more  imperfect.  In  the 
opinion  of  Munk,  if  the  extirpations  are  considerably  enlarged  the 
restitution  of  function  is  never  complete. 

§  8.  That  explanation  of  the  phenomena  which  regards  the  va- 
rious cerebral  regions,  that  seem  somehow  specially  connected  with 
motor  activities,  as  true  "  motor  centres," — that  is,  as  areas  of  the 
cerebral  cortex  that  have  for  their  peculiar  function  the  initiating 
of  definite  motor  impulse  on  occasion  of  the  idea  and  volition  to 
move  definite  portions  of  the  peripheiy  of  the  body, — is  rejected 
by  Munk.  All  the  regions  marked  G — J,  belong  rather  to  what  he 
calls  the  "feeling-sphere"  of  the  cerebral  hemispheres.  It  is  an 
undoubted  fact  that  the  definite  co-ordination  of  the  limbs,  from  the 
higher  cerebral  centres,  depends  upon  feelings  of  contact  and  press- 
ui'e  of  the  skin,  and  upon  muscular  feelings  or  so-called  feelings  of 
innervation.  The  effects  of  extirpating  centres  like  (C),  (D),  and 
(E),  is  due,  therefore,  first  to  the  sudden  loss,  and  subsequently  to 
'  Ueber  d,  Functionen  d.  Grosshinirinde,  p.  47. 


MOTOR   AREAS"    OF    THE   MOl^iKEY. 


273 


the  gradual  restitution  of  these  feelings,  and  of  their  correspond- 
ing mental  representations,  with  respect  to  given  groups  of  mus- 
cles. 

Schiff '  agrees  with  Munk  in  the  view  that  the  real  loss  of  function 
due  to  the  extirpation  of  the  above-mentioned  cerebral  regions  is 
sensory  rather  than  motor  ;  he  considers  that  the  imj)airment  of  the 
power  of  moving  these  parts  is  only  an  expression  of  the  loss  of  the 
sense  of  touch  in  the  same  parts  ;  in  other  words,  it  is  tactile  an- 
aesthesia. He  calls  attention  to  the  significant  fact  that  an  animal 
thus  operated  upon  will  freely  allow  parasites  and  insects  to  gather 
on  that  surface  of  the  skin  whose  corresponding  cortical  area  has 
been  removed.     Schiff  also  finds  that  the  use  w^hich  the  higher  apes 


Fig.  i 


-Areas  on  the  Brain  of  the  Monkey.     (According  to  Munk.)     The  letters  have  the  same 
reference  as  in  tho  preceding  figure. 


make  of  their  limbs  for  grasping  the  rounds  of  a  trellis  or  ladder 
is  not  permanently  impaired  by  removing  to  considerable  depth 
the  convolutions  about  the  central  sulcus,  unless  the  trellis  or  ladder 
be  turned  at  an  angle  of  60''  to  70°,  so  as  to  convert  the  animal's 
walking  into  climbing.  Apparently  the  animal  cannot  climb  be- 
cause he  is  unable  to  form  a  mental  picture  of  the  next  round  so 
as  to  i-each  out  and  grasp  it.  Schiff  therefore  concludes,  that  "  all 
motions  are  suppressed  (by  extirpating  the  cerebral  substance) 
which,  on  being  excited  by  the  higher  senses,  receive  a  special 
supervision  on  the  side  of  cerebral  sense,  in  relation  to  direction, 
extent,  and  succession."  He  also  asserts,  in  opposition  to  the 
conclusions  of  Goltz,  that  the  injured  animal  never  recovers  the 

1  See  Pfliiger's  Archiv,  xxx.  (1883),  pp.  313  flf. 
18 


274  STiMULATioisr  AjStd  extirpation. 

powers  it  has  once  really  lost ;  in  other  words,  it  is  not  possible  to 
extir^Date  any  of  the  centres,  excitation  of  which  produces  a  given 
motion,  without  effecting  some  permanent  result. 

§  9.  The  conclusions  of  Munh  and  Schiff  undoubtedly  have  cer- 
tain facts  of  experiment  in  theu"  favor,  but  they  can  scarcely  be  said 
either  to  cover  all  the  facts  or  to  be  wholly  consistent  with  certain 
pai'ticular  ones.  Goltz  '  agTces  substantially  with  Munk  in  finding 
that  destruction  of  the  cerebral  substance  of  the  frontal  lobe  causes 
the  animal  to  execute  movements  of  the  limbs  of  the  opposite  side 
in  a  coarse  and  unskilful  manner.  He  also  finds  that  the  tactile 
sense  is  temporarily  impaired,  although  by  giving  increased  atten- 
tion the  animal  is  able  to  feel  the  slightest  touch  on  any  area  of 
the  skin.  Indeed,  deep  and  extensive  lesions  in  this  region  may 
be  followed  by  hj^DcrEesthesia.  The  muscular  sense,  on  the  other 
hand,  seems  permanently  to  suffer.  Goltz's  conclusions  are  squarely 
contradictory  of  all  those  which  find  any  permanent  laming  of  any 
muscle  as  the  result  of  even  the  most  extensive  destruction  of  the 
cortical  substance  in  the  so-called  "motor  field."  His  theory  lays 
more  emphasis  on  the  general  impairment  of  intelligence  which  re- 
sults fi'om  removing  any  considerable  amount  of  the  substance  of 
the  brain,  from  whatever  region  it  may  be  taken. 

A  still  more  recent  investigator^  calls  attention  anew  to  the  facts 
that  an  animal  deprived  of  the  "  motor  sphere  "  cannot  use  the  ex- 
tremities as  hands  ;  cannot  hold  the  foot  out  on  call,  or  push  away 
the  hand  by  which  its  chin  is  grasped,  or  stretch  out  the  limb  so 
as  to  grasp  the  dish  containing  its  food.  These  phenomena  imply, 
he  thinks,  some  severance  between  the  organ  of  will  and  the  nerves 
which  execute  the  will.  The  motor  centres  are  to  be  limited,  it  is 
claimed,  almost  exclusively  to  the  gyrus  sigmoideus,  and  those  for 
feelings  of  the  skin  and  muscles  to  the  region  lying  above  the  fis- 
sure of  Sylvius. 

On  attempting  to  reconcile  all  the  results  of  experiment  upon 
the  animals  with  one  another,  and  with  the  facts  of  human  pathol- 
ogy, it  must  be  admitted  that  great  difficulty  is  experienced ;  and 
even  more  difficult}'^  when  the  effort  is  made  to  frame  a  consistent 
theory  which  shall  cover  them  all.  On  the  whole,  however,  it 
seems  obvious  that  a  certain  region  or  sphere  of  the  cortex  of  the 
brains  of  the  higher  animals  is  entitled  to  be  called  "  motor"  in  a 
special  sense ;  and  that  this  region  corresponds  in  a  general  way  to 

'  See  his  article  in  Pfli'ger's  Archiv,  xxxiv.  (1884).  pp.  450  fP. 

"  Bechterew,  art.  "  Wie  siiid  die  Ersclieiuiuigen  zu  verstelien  die  nach 
Zerstorimg  des  motorischeu  Riudeufeldes  an  Thiereu  auftreteu ;  "  Pfliiger, 
XXXV.  (1885),  pp.  137  tf. 


FROM   AlSriMAtS   TO   MAN.  275 

that  which  (as  we  shall  soon  see)  pathology  indicates  as  specially 
motor  in  the  case  of  man.  Stimulation  of  various  minute  areas  in 
this  region  is  followed  by  the  movement  of  definite  muscles  of  the 
body  ;  extirpation  of  this  region  in  its  entirety,  or  in  part,  is  fol- 
lowed by  special  disturbances  of  the  motor  functions  of  the  animal. 
These  disturbances  are  not  of  the  kind  which  indicates  so  much 
a  laming  of  any  particular  muscle,  as  a  loss  of  cerebral,  and  so  in- 
telligent, quality  in  respect  to  the  handling  of  the  extremities. 
They  probably  imply  more  or  less  of  all  those  various  kinds  of  psychi- 
cal disturbances  and  impairments  of  function,  by  some  one  of  which 
exclusively  the  different  investigators  are  wrongly  inclined  to  ac- 
count for  the  phenomena  which  they  observe.  Extensive  lofeses  of 
cerebral  substance  in  the  motor  region  result  in  the  loss  of  those 
tactile  sensations  and  muscular  sensations,  by  means  of  which  the 
animal  localizes  and  interprets  the  meaning  of  objects,  and  adapts 
the  finer  movements  of  its  limbs  accordingly.  They  also  impair 
the  power  to  express  the  volition  of  the  animal  by  motor  impulses 
started,  in  accordance  with  the  sensations  and  images  of  motion,  in 
the  appropriate  area  of  the  brain.  Moreover,  such  loss  of  the 
powers  of  sensation,  sense-perception,  and  skilful  motion,  neces- 
sarily implies  more  or  less  of  loss  of  intelligence. 

§  10.  It  will  always  be  difficult  to  designate  precisely  what  fac- 
tors in  the  animal's  complex  sensory-motor  activities  drop  out  as  the 
result  of  the  removal  of  a  certain  area  of  cortical  substance  from  the 
brain  of  a  dog  or  monkey  ;  and  whether  these  factors  are  exclusively 
sensory  or  exclusively  motor,  rather  than  both  sensory  and  motor. 
It  is  doubtful  if  enough  can  ever  be  known,  concerning  the  mental 
life  of  the  dog  or  the  monkey,  to  determine  confidently  in  this  way 
the  question  of  the  localization  of  psycho-physical  functions.  The 
phenomena  of  human  pathological  cases  indicate,  however,  that  in 
man  the  corresponding  general  area  of  the  cerebrum — that  is,  the 
convolutions  on  both  sides  of  the  central  fissure  and  the  lobulus 
paracentralis — is  especially  concerned  in  both  sensory  and  motor  fac- 
tors for  co-ordinated  action  of  the  limbs.  Without  adducing  further 
confirmatory  evidence  from  experiment  upon  other  animals,  we 
pass  to  the  consideration  of  the  evidence  from  human  pathology. 
The  results  of  experiments  in  stimulation  and  extirpation  upon  the 
lower  animals  are  not  to  be  transferred  in  toto,  as  a  matter  of 
course,  to  the  human  cerebrum  ;  they  are  rather  to  be  consulted 
as  indicating  the  precise  nature  of  the  questions  to  be  proposed  to 
pathology,  and  of  the  answers  to  these  questions  which  are  antece- 
dently probable. 

From  this  point  onward  our  chief  reliance  must  be  placed  upon 


276 


HUMAN   PATHOLOGICAL   CASES. 


Exner's  '  careful  and  scientifically  classified  investigations.  The 
method  pursued  by  this  investigator  is  described  at  length  by  him- 
self. °  Exner  began,  with  true  German  thoroughness,  by  reading 
several  thousand  cases  of  cerebral  disease  which  had  been  followed 
by  post-mortem  examination  ;  the  catalogue  of  works  thus  consulted 
by  him  occupies  more  than  twenty  pages.     From  all  these  cases  he 


Fig.  87. — Lateral  View  of  the  Human  Brain.  (Schematic,  Ecker.)  F,  frontal,  P,  parietal,  O, 
occipital,  and  T,  temporo-sphenoidal  lobes.  S,  fiBsure  of  Sylvius,  with  S'.  the  horizontal,  and 
8",  the  ascending  ramus  ;  C,  sulcus  centralis ;  A,  anterior,  and  B,  posterior,  central  convolu- 
tions ;  Fl,  ra,  F8,  superior,  middle,  and  inferior  frontal  convolutions ;  fl,  superior,  f2,  infe- 
rior frontal  sulci;  f3,  sulcus  praeceiiiralis;  PI,  superior,  and  P2,  inferior  parietal  lobule;  the 
latter,  the  gyrus  supra  marginalis,  and  P9',  the  gyrus  angularis  ;  ip,  sulcus  interpiirietalis :  cm, 
end  of  calloso-margii'al  fissure  ;  Ol.  02,  08,  occipital  convolutions  ;  po,  parietooccipital  fissure  ; 
o,  transverse,  and  o2,  inferior  longitudinal  sulcus;  Tl,  T2,  T3,  tempore  sphenoidal  convolu- 
tions; and  tl,  t2,  tempero  sptienoldal  fissures. 


then  made  a  collection  of  such  only  as  could  safely  form  the  basis 
of  a  scientific  induction.  The  conditions  of  admittance  into  this 
collection  were  as  follows :  Both  the  history  of  the  disease  and  the 
description  of  the  post-moi'tem  condition  must  be  trustworthy,  full, 

'  Untersuchnngen  iiher  d.   Localisation  d.  Functionen  in  d.  Grossliirnriude 
d.  Menscheii.     Wien,  1881. 
•'  Ibid,  p.  G  f. 


THE   METHODS   OF   KECKONING. 


277 


and  unambiguous  ;  and  there  must  have  been  no  other  lesion  than 
the  one  in  the  cerebral  cortex,  either  elsewhere  in  the  brain  or  in 
the  spinal  cord,  to  complicate  the  legitimate  inferences.  Only  two 
exceptions  to  the  latter  rule  were,  for  reasons  peculiar  to  themselves, 
admitted.  Nearly  all  cases  in  which  symptoms  indicative  of  diffuse 
meningitis  occurred  were  also  excluded.     In  this  cautious  way  one 


Fig.  88. — View  of  the  Human  Brain  from  Above.     (Schematic,  Ecker.)    The  letters  have  the 
same  reference  as  in  the  preceding  figure. 


hundred  and  sixty-nine  test-cases  were  secured  from  the  thousands 
recorded.  These  test-cases  were  then  tabulated  on  three  sets  of 
maps,  according  to  the  following  methods  of  induction :  (1)  The 
method  of  negative  cases,  (2)  the  method  of  "reckoning  per  cent.," 
(3)  the  method  of  positive  cases. 

The  method  of  negative  cases  (if  the  number  of  such  cases  were 
large  enough)  would  result  in  showing  what  regions  of  the  cerebral 
hemispheres,  if  any,  are  not  necessarily  connected  with  motor  or 


278 


HUMAN   PATHOLOGICAL   CASES. 


sensory  functions — both,  or  either  one  respectively.  The  charts 
constracted  by  this  method  would,  accordingly,  have  only  those 
convolutions  and  parts  of  convolutions  left  blank,  or  unmarked, 
in  which  no  lesion  had  occurred  that  was  not  followed  by  some 
given  kind  of  motor  or  sensory  disturbances.  The  method  of  per- 
centage was  designed  to  show  the  amount  of  probability  that  a 
given  small  area  of  the  cerebral  cortex  will  be  hit  by  disease,  as 
it  were,  in  case  the  lesion  has  been  followed  by  a  given  kind  of 
motor  or  sensory  disturbance.  For  this  purpose  the  entire  sur- 
face of  one  hemisphere  was  mapped  out  into  three  hundred  and 


A    9 


Fig.  89. — Median  Aspect  of  the  Right  Hemisphere.  (Schematic,  Ecker.)  CO,  corpus  callosum. 
G-yri :  G-f,  fornicatns  ;  H,  hippocampi  (with  its  sulcus,  h),  and  TJ,  uncinatus  :  PI',  praecuneus; 
Oz,  cuneus ;  oc,  calcarine  fissure,  with  its  two  rami,  oc'  and  oc'' ;  D,  gyrus  descendens  ;  T4,  the 
lateral,  and  T5,  the  medial,  gyrus  occipito-iemporal.R. 


sixty-seven  quadrilateral  areas,  all  small  and  yet  of  somewhat  dif- 
fei'ent  sizes.  As  the  different  selected  cases  were  recorded  by 
painting  the  area  of  the  lesions  on  this  set  of  maps,  the  intensity  of 
the  color  used  would,  of  course,  deepen  in  proportion  to  the  cer- 
tainty of  a  connection  between  that  particular  area  and  some  par- 
ticular sensory  or  motor  function.  Thus  a  joerfect  black  would 
indicate  one  hundred  per  cent,  of  cases  in  which  a  given  quadri- 
lateral was  hit  when  a  given  disturbance  of  function  had  followed  ; 
pure  white,  nought  per  cent,  of  such  cases.  The  third  method  (that  of 
positive  cases)  is  the  one  usually  relied  upon  to  prove  (?)  the  theory 
of  localization  of  cerebral  function  from  pathology  ;  it  is  justly  re- 
garded by  Exner  as  the  least  conclusive,  as  never  of  itself  forming 


FIELD   OF   LATENT   LESIOISTS.  279 

a  basis  for  anything  beyond  conjecture.  Its  principle  is  the  as- 
sumption that  the  region  where  the  lesions  connected  with  certain 
disturbances  are  most  thickly  crowded  together,  is  the  required 
cortical  area  with  its  specific  function. 

§  11.  The  result  of  Exner's  comprehensive  induction  from  patho- 
logical cases,  as  based  on  all  three  of  the  methods  just  described, 
fixes  almost  beyond  doubt  the  so-called  "motor  areas"  of  the  hu- 
man cerebrum.  [For  understanding  Exner's  induction,  consulta- 
tion of  Ecker's  charts,  found  on  p.  276f.,  figs.  87,  88,  and  89,  will  be 
found  helpful.]  The  field  of  wholly  ^'latent  lesions" — that  is,  of  le- 
sions which  are  not  necessarily  followed  by  any  disturbances  of 
either  sense  or  motion — covers  a  large  part  of  the  surfaces  of  both 
hemispheres  ;  it  is  not,  however,  precisely  the  same  for  them  both. 
While  Exner's  collection  of  cases  comprised  67  lesions  of  the  right 
hemisphere,  and  101  of  the  left,  the  absolute  number  of  latent 
lesions  was  the  same  (namely,  20)  for  both  hemispheres.  The 
chances  that  a  lesion  of  the  right  hemisphere  will  not  be  followed 
by  any  disturbance  of  function  are,  therefore,  about  fifty  per  cent, 
greater  than  the  chances  that  the  same  thing  will  occur  in  the  left 
hemisphere.  On  the  right  hemisphere  the  entire  surface,  with  the 
exception  of  the  two  gyri  centrales,  the  lobidus  paracentralis,  and 
certain  small  portions  on  the  convex  and  inferior  surfaces  of  the 
occipital  lobe  is  latent.  On  the  left  hemisphere  the  latent  region 
is  of  less  extent.  This  result  may  be  regarded  as  a  restatement, 
on  a  basis  of  scientific  induction,  of  the  well-known  fact  that  ex- 
tensive lesions  can  occur  in  the  frontal,  temporal,  and  occipital 
lobes,  without  being  followed  by  any  sensory  or  motor  disturb- 
ances. But  it  also  confirms  the  impression  that  the  portions  of 
the  cerebral  cortex  lying  about  the  fissure  of  Rolando  are  entitled 
to  be  called  "  the  exquisitely  motor  parts  of  the  cortex." 

Yet  more  precisely,  the  motor  region  on  either  hemisphere  may 
be,  according  to  Exner,  marked  out  by  the  method  of  negative 
eases,  and  by  the  method  of  percentage  of  cases.  The  former  meth- 
od shows  that,  for  the  upper  extremities,  the  corresponding  cortical 
region  on  the  right  hemisphere  is  the  lobulus  paracentralis,  the  gyrus 
centralis  anterior  (with  the  exception  of  a  small  part  of  its  lower 
end)  and  the  upper  half  of  the  gyrus  centralis  posterior.  The  latter 
method  further  confirms  the  foregoing  conclusion.  It  shows  that 
the  "absolute  field"  for  the  upper  extremities — the  field,  that  is, 
within  which  lesions  are  always  followed  by  impaired  motion  of 
these  extremities — covers  quite  completely  the  same  parts  of  cere- 
bral convolutions  ;  while  the  "  I'elative  field,"  or  portion  in  which 
more  than  fifty  per  cent,  of  cases  of  lesions  are  followed  by  similar 


280  HUMATq"   PATHOLOGICAL   CASES. 

disturbances,  extends  over  the  remaining  half  of  the  gyrus  centralis 
posterior,  the  posterior  third  or  half  of  the  three  frontal  convolu- 
tions, the  anterior  half  of  the  parietal  lobe,  and  more  of  the  neighbor- 
ing median  surface.  Corresponding  to  the  better  motor  education 
of  the  right  arm  is  the  fact  that  its  motor  region  on  the  left  hemi- 
sphere is  more  extended.  Here  the  absolute  field  comprises  the 
lobulus  paracentralis,  the  three  upper  quarters  of  both  gyri  centrales, 
and  the  greater  part  of  the  upper  parietal  lobe.  Portions  of  the 
median  surface  of  the  occipital  lobe  may  also  belong  to  this  field. 
The  relative  field  for  the  upper  extremity  on  the  left  hemisphere 
includes  the  posterior  half  of  the  gyrus  frontalis  superior,  almost 
the  entire  convex  surface  of  the  other  frontal  gyri,  the  parietal  lobe 
at  large,  and  the  upper  part  of  the  occipital  lobe. 

More  specific  localization  of  cerebral  areas,  corresponding  to  the 
different  parts  of  the  upper  extremities,  can  as  yet  be  accomphshed 
only  with  much  less  confidence  and  in  a  conjectural  way.  The 
method  of  positive  cases  seems  to  designate  the  gyrus  centralis  an- 
terior as  the  special  cortical  area  for  the  hand  ;  with  a  probability 
that  the  area  for  the  extensors  of  the  hand  lies  in  its  middle  part, 
and  the  area  of  the  thumb  somewhat  below  in  the  same  gyrus. 

§  12.  Exner's  collection  contained  75  cases  of  disturbances  of 
motion  in  the  loiver  extremities  ;  26  lesions  being  on  the  right,  49 
on  the  left  hemisphere.  The  methods  both  of  negative  cases  and 
of  percentage  agree  in  indicating  that  the  "  absolute  "  cortical  field  of 
the  left  leg  comprises  the  lobulus  paracentralis,  the  uppermost  third 
(as  far  as  the  lower  end  of  the  sulcus  frontalis  superior)  of  the 
gyrus  centralis  anterior,  portions  of  the  corresponding  third  of  the 
gyrus  centralis  posterior,  and  some  small  areas  behind  and  below  on 
the  lobulus  quadratus, — all,  of  course,  in  the  right  hemisphere.  The 
"  relative  field  "  of  the  same  limb  on  the  same  cerebral  hemisphere 
includes  both  lower  thirds  of  the  central  convolutions,  the  back 
parts  of  the  frontal  convolutions,  the  parietal  lobules,  and  the  up- 
per portion  of  the  occipital  lobe.  On  the  median  surface  of  the 
brain,  the  posterior  part  of  the  gyrus  frontalis  superior  and  the 
anterior  half  of  the  lobulus  quadratus  belong  to  this  field.  On  the 
left  hemisphere  the  absolute  cortical  field  for  the  right  leg  includes 
the  lobulus  paracentralis,  the  upper  half  of  the  gyrus  centralis  pos- 
terior, and  most  of  the  upper  portion  of  the  parietal  lobe.  A  small 
lateral  part  of  this  lobe,  and  on  the  median  surface  the  lobulus 
quadratus,  and  perhaps  the  cuneus,  must  be  added  to  complete  the 
relative  field  of  this  lower  extremity.  Exner  does  not  consider  it 
possible,  as  yet,  to  be  more  precise  in  designating  the  cerebral  fields 
for  the  lower  limbs  of  man. 


FIELDS   OF   FACE,  TOJSTGUE,  A]S^D   NECK.  281 

§  13.  On  comparing  with  each  other  the  foregoing  conclusions, 
it  is  apparent  that  the  absolute  field  for  the  upper  extremities  en- 
tirely covers  the  corresponding  field  for  the  lower  extremities  ;  but 
the  gyrus  centralis  anterior  and  lower  half  of  the  gyrus  centralis 
posterior  belong  only  to  this  field  for  the  upper  extremities.  The 
relative  fields,  too,  for  both  arms  and  legs,  have  a  similar  relation  in 
extent  and  intensity.  There  is  considerably  greater  probability, 
therefore,  that  a  lesion  of  a  given  size  in  the  motor  region  will  af- 
fect the  arms  than  that  it  will  affect  the  legs  ;  indeed,  the  collection 
of  Exner  shows  but  one  case  in  which  the  motions  of  the  legs  were 
disturbed  and  not  those  of  the  arms.  This  greater  "  sensitiveness  " 
— if  we  may  so  speak — of  the  cortical  region  of  the  upper  extrem- 
ities, corresponds  to  the  fact  that  their  motion  is  more  distinc- 
tively cerebral  and  intelligent  than  that  of  the  lower  extremities. 

§  14.  In  this  same  "  exquisitely  motor  "  region  of  the  cerebral 
cortex,  and  in  the  most  nearly  adjacent  regions  of  the  frontal  and 
parietal  lobes,  certain  other  cerebral  fields  corresponding  to  definite 
muscles  or  groups  of  muscles  may  be  localized,  conjecturally.  By 
the  method  of  percentage  the  cerebral  area  for  those  muscles  to 
which  the  facial  nerve  is  distributed  may  be  rather  indefinitely  in- 
dicated as  lying  in  the  lower  half  of  the  gyrus  centralis  anterior,  and 
lower  third  of  the  gyrus  centralis  posterior,  on  the  right  hemisphere  ; 
while,  on  the  left  hemisphere,  it  appears  to  be  moi'e  definitely  fixed 
at  a  small  strip  that  belongs  to  the  gyrus  centralis  anterior,  and  lies 
between  the  places  where  the  inferior  and  superior  frontal  gyri 
spring  from  this  central  gyrus,  but  nearer  the  first  of  the  two. 
Both  methods  of  induction  apparently  unite  in  indicating  the 
cortical  region  for  the  tongue  as  lying  where  the  middle  and  lower 
frontal  gyri  meet  with  the  anterior  central  gyrus.  In  the  nine  cases 
of  the  collection  in  which  the  muscles  of  head  and  neck  were  af- 
fected, the  lesions  were  all  situated  in  one  of  the  central  convolu- 
tions ;  but  a  more  definite  localization  within  the  limits  of  these 
convolutions  does  not  apjjear  to  be  possible.  As  to  the  localization 
also  of  the  cerebral  field  for  the  muscles  of  the  eyeball,  including 
that  for  raising  the  upper  lid,  pathology  is  able  only  to  say  in  a 
general  way  that  this  field  appears  to  fall  within  the  general  motor 
area  as  thus  far  pointed  out.  Exner  thinks  it  certain  that  the 
rectus  internus  muscle  of  one  side,  and  the  rectus  externus  of  the 
other  side,  are  innervated  from  the  same  hemisphere  of  the  brain. 
This  we  should  also  argue  from  their  ordinary  physiological  func- 
tion. 

§  15.  Positive  cases  of  a  nature  to  strengthen  the  foregoing  in- 
duction as  to  the  cerebral  areas  especially  connected  with  the  upper 


282  HUMAN   PATHOLOGICAL   CASES. 

and  lower  extremities  might  be  indefinitely  multiplied.  Especially 
interesting  are  those  where  disuse,  through  accident  or  disease,  of 
one  of  these  extremities  has  been  found,  post-mortem,  to  have  re- 
sulted in  atrophy  of  the  corresponding  cortical  fields.  That  is  to 
say,  the  cortical  region,  being  unused  on  account  of  the  loss  of 
function  in  the  peripheral  member,  has  itself  paid  the  penalty  of 
all  failure  to  exercise  the  normal  functions ;  it  has  lost  in  size  and 
strength.  For  example,  atrophy  of  the  upper  end  of  the  gyrus 
centralis  anterior  of  the  right  hemisphere,  and  of  its  prolongation 
in  the  lohulus  paracenlralis,  was  in  one  case  found  to  have  resulted 
from  the  amputation  of  the  left  leg  twenty  years  before  death. 

§  16.  The  conclusions  of  other  authorities  as  to  the  motor  re- 
gions of  the  cerebral  cortex  in  man — especially  of  Lepine,'  and  of 
Charcot  and  Pitres'^ — as  based  on  pathology,  confirm  those  of  Exner 
in  the  main,  as  well  as  also  in  some  interesting  particulars ;  any  di- 
vergences arise  almost  wholly  from  the  effort  to  make  distinctions 
more  nicely  than  the  present  condition  of  the  facts  will  warrant. 
The  most  general  conclusions  of  these  investigators  may  be  summed 
up  as  follows  :  ^  "  The  cortex  of  the  cerebral  hemispheres  in  man 
may  be  divided,  functionally,  into  two  parts  ;  motor  and  non-motor, 
according  as  destructive  lesions  do  or  do  not  cause  permanent  par- 
alysis of  the  opposite  side  of  the  body."  .  .  "  The  motor  zone  in- 
cludes only  the  ascending  frontal  and  ascending  parietal  convolutions 
and  the  paracentral  lobule."  It  may  be  concluded  then,  as  a  well-es- 
tablished induction,  that  the  convolutions  on  either  side  of  the  fissure 
of  Rolando  (the  gyri  centrales  anterior  and  posterior)  and  the  con- 
nected lobule  on  the  median  surface  of  the  brain  (lohulus  paracen- 
tralis)  are  in  the  highest  degree  especially  connected  with  the  mo- 
tion of  the  extremities  of  the  body  ;  that  adjacent  parts  of  the 
frontal  and  parietal  lobes  are  thus  connected  in  a  less  degree  ;  that 
the  cortical  region  for  the  arms  lies,  on  the  whole,  anterior  to  that 
of  the  legs  ;  and  that,  probably,  the  region  for  the  hand  is  near  the 
middle  part  of  the  front  central  convolution,  and  that  for  the  tongue 
where  the  middle  and  lower  frontal  convolutions  meet  the  front 
central.  More  precise  localization  of  the  motor  functions  of  man 
must  as  yet  be  made  with  a  lower  degree  of  confidence.  Beyond 
these  general  statements  lies  the  undefined  field  of  conjecture. 

§  17.  It  cannot  be  said  that  histology  and  comparative  anatomy 

'  Localisation  dans  les  maladies  cerebrales.     Paris,  1875. 

^  Localisation  dans  les  maladies  du  cerveau,  Paris,  1876;  Revne  mensuelle 
de  Med.  et  de  Chir..  1877-1879;  Etude  critique  et  clinique  de  la  doctrine 
dans  I'ecorce  des  hemispheres  cerebraux  de  I'homme,  Paris,  1883. 

''  See  Brain,  July,  1884,  p.  270  f. 


TESTIMONY    OF   HISTOLOGY. 

much  affect  the  strength  of  the  argument  for  the  localization  of  the 
cerebral  motor  regions,  as  derived  from  experimentation  and  pa- 
thology ;  whatever  evidence  they  do  furnish,  however,  is  confirma- 
tory of  the  conclusions  reached  above.  In  this  connection  refer- 
ence maybe  made  to  the  conclusion  of  Meynert,'  that  the  paths 
of  the  sensory  nerves  run  more  toward  the  occipital,  and  those  of 
the  motor  nerves  toward  the  frontal  region  of  the  cerebrum.  The 
existence  of  nerve-cells  of  gigantic  size,  resembling  those  found  in 
the  motor  region  of  the  spinal  cord,  which  Betz  discovered  in  the 
motor  regions  of  the  cerebrum  of  the  dog,  the  monkey,  and  of  man, 
is  an  indication  in  the  same  direction.  It  should  also  be  mentioned 
that  the  pathological  researches  of  Pitres  ^  into  the  results  of  lesions 
in  the  medullary  substance  lying  between  the  cerebral  cortex  and 
the  basal  ganglia,  seem  to  show  that  such  as  occur  in  the  fronto- 
parietal portion  of  this  substance  cause  paralysis  of  motion  and  de- 
generation of  the  motor  tracts.  Finally,  the  general  structure  of  the 
cerebrum  and  the  courses  of  its  nerve-tracts,  as  already  considered 
(Part  I.,  Chapters  11.  and  IH.),  are,  in  the  main,  accordant  with 
the  facts  of  experimentation  and  pathology. 

§  18.  The  remarkable  degree  of  coincidence  in  locality  which 
obtains  among  those  circles  whose  extirjDation  is  followed  by  dis- 
turbances of  motion  (disturbances  due,  in  the  opinion  of  Hitzig, 
to  destruction  of  the  physical  basis  of  the  animal's  control  over  its 
limbs,  but,  in  the  opinion  of  Schiff,  rather  due  to  tactile  anaesthe- 
sia) suggests  the  following  question  :  Is  not  the  cortical  field  of 
tactile  sensation  in  the  extremities  of  man  coincident,  in  the  main, 
or  even  in  particular,  with  the  field  for  the  motion  of  the  same  ex- 
tremities? An  affirmative  answer  to  this  question  woiild  seem 
reasonable,  even  prior  to  experimental  and  pathological  evidence. 
The  sensory  and  motor  mechanisms  are,  of  necessity,  most  inti- 
mately connected,  locally,  in  all  the  central  organs.  This  state- 
ment is  certainly  true  of  the  spinal  cord  and  of  the  inferior  parts 
of  the  braiu.  Moreover,  in  consciousness  the  sensations  which 
guide  the  volitions  in  all  the  finer  uses  of  the  peripheral  parts  of  the 
body  are  very  promptly,  and  even  almost  inextricabl}',  interwoven 
with  the  volitions.  In  walking,  talking,  handling  a  tool,  or  playing 
a  musical  instrument,  to  be  unable  to  experience  certain  delicate 
sensations  is  to  be  unable  to  will  the  execution  of  corresponding 
nicely  adjusted  motions  ;  whereas  the  appearance  of  the  associated 
sensations  may  instantaneously  call  forth  the  requisite  volitions. 
It  would  seem,  then,  that  the  cerebral  mechanism  for  both  the 

*  Sitzgsbr.  d.  Wiener  Acad.,  LX.,  heft  iii.,  p.  455  f. 
^  Lesions  du  centre  ovale.     Paris,  1877. 


284  HUMAN   PATHOLOGICAL   CASES. 

sensory  and  the  voluntary  motor  factors  of  these  complex  functions 
must  be  composed  of  elements  having  the  closest  local  connection. 
Certain  indisputable  facts  of  pathology  form,  however,  a  strong 
objection  to  such  an  identification  of  the  cerebral  fields  of  motor 
function  and  tactile  sensory  function.  Many  cases  of  motor  dis- 
turbance occur  without  the  disturbance  of  sensation  in  the  same  ex- 
tremity ;  and  cases  of  sensory  disturbance  withoiit  corresponding 
motor  disturbance,  although  much  less  frequent,  are  by  no  means 
very  rare.  How,  then,  can  these  facts  of  pathology  be  reconciled 
with  any  hypothesis  which  locates  in  the  same  cerebral  region  the 
so-called  "  fields  "  for  both  classes  of  function  ? 

The  answer  which  Exner  gives  to  the  foregoing  question  is  per- 
tinent, but  not  wholly  conclusive.  No  absolute  cortical  field  for 
disturbances  of  tactile  sensation  in  the  extremities  of  the  body  can, 
indeed,  be  pointed  out ;  that  is  to  say,  there  is  no  portion  of  the 
cerebral  cortex,  lesions  of  which  are  invariably  and  necessarily  fol- 
lowed by  tactile  anaesthesia,  hyperaesthesia,  etc.,  in  definite  parts  of 
the  periphery.  But  that  the  entire  relative  field  of  sensations  of  touch 
in  the  extremities  corresponds  with  that  of  the  motor  activities,  is 
made  highly  probable  by  the  method  of  positive  cases.  After  ex- 
cluding doubtful  cases — in  which  the  patient  comjplained  rather  in- 
definitely of  a  feeling  of  "  heaviness"  or  "  numbness,"  etc.,  in  some 
area  of  muscle  or  skin — Exner's  collection  was  found  to  contain 
22  cases  where  marked  disturbances  of  tactile  sensations  seemed 
clearly  made  out.  Of  these  22  cases  no  fewer  than  16  were  located 
wholly  in  the  two  central  convolutions ;  and  3  of  the  remaining  6 
extended  for  several  millimetres  into  the  same  convolutions.  Of 
those  still  remaining,  the  one  farthest  removed  from  the  "  exquisitely 
motor  "  region  was  in  the  gyrus  angularis,  and  therefore  in  a  portion 
of  the  relative  motor  field  which  has  a  considerable  per  cent,  of  in- 
tensity. 

On  the  basis  of  so  complete  an  agreement  of  the  positive 
cases,  Exner  feels  warranted  in  affirming  that  "the  tactile  cortical 
fields  for  the  different  divisions  of  the  body  coincide  in  general 
with  their  motor  cortical  fields."  It  is  to  be  noted,  moreover,  that 
the  percentage  of  the  cases  of  disturbance  of  tactile  sensations 
occurring  on  the  right  hemisphere  is  more  than  twice  as  large  as 
that  of  the  left.  Sensibility  seems,  then,  to  be  the  predominating 
function  of  the  right  hemisphere,  as  motion  is  of  the  left.  This 
fact,  when  taken  in  connection  with  the  greater  liability  of  the  left 
hemisphere  to  be  the  seat  of  cerebral  disease,  accounts  in  part  for 
the  less  frequent  occurrence  of  sensory  disturbances  following  le- 
sions in  this  general  area.    Moreover,  we  are  warranted  in  assum- 


THE   CONCLUSIONS    OF   LUCIANI.  285 

ing  that  the  cortical  fields,  in  which  the  nervous  impulses  occasion- 
ing tactile  sensations  are  projected,  are  connected  with  each  other, 
and  with  the  ascending  sensory  tracts,  in  a  very  complicated  way. 
The  manner  of  this  connection  is  doubtless  different  for  the  different 
areas  of  muscle  and  skin.  Nor  does  it  appear  that  the  sensory  areas 
are  so  well  differentiated  as  the  corresponding  motor  areas ;  although 
one  case,  at  least,  can  be  pointed  out  in  which  loss  of  sensation  in 
the  thumb  and  index-finger  was  the  definite  result  of  a  lesion  of 
the  very  limited  cortical  region  already  conjecturally  assigned  to 
these  members.  Finally,  it  must  be  remembered  that  those  descrip- 
tions of  pathological  cases  on  which  all  our  inductions  have  hitherto 
been  based,  are  very  liable  to  be  faulty  with  respect  to  slight  dis- 
turbances of  sensibility. 

It  is  a  general  conclusion,  then,  which  is  entitled  to  a  large  de- 
gree of  confidence,  that  both  the  gyri  centrales,  the  lobulus  para- 
centralis,  and  the  most  nearly  adjacent  parts  of  the  frontal  and 
parietal  convolutions,  constitute  a  cortical  region  especially  related 
to  both  the  motor  and  the  sensory  functions  of  the  extremities  of 
the  body. 

The  view  of  Exner  concerning  the  nature  of  the  motor  area  in 
man  is,  on  the  whole,  greatly  strengthened  by  the  most  recent  con- 
clusions of  Luciani.  This  experimenter  finds  '  that  total  or  partial 
extirpation  of  the  "  motor  zone  "  in  the  dog  and  the  monkey  is 
uniformly  followed,  not  only  by  motor  paralysis,  but  also  by  cuta- 
neous and  muscular  anaesthesia.  The  "  motor "  sphere  and  the 
"  tactile  "  sphere  are  largely  coincident  in  these  animals  ;  and  "  in 
all  experiments  upon  the  tactile  sphere  there  was  a  manifest  and 
constant  crossing  of  the  relations  between  the  peripheral  sensory 
fibres  and  their  respective  cortical  centres."  "What  one  calls 
'motor  zone  '  is  the  central  focus  of  the  large  portion  of  the  senso- 
rial sphere  visible  on  the  external  aspect  of  the  hemisphere." 

§  19.  The  testimony  of  the  facts  upon  which  reliance  must  be 
placed  in  the  effort  to  localize  the  cerebral  field  for  sensations  of  sight 
and  hearing  in  man  is  by  no  means  so  satisfactory  as  the  foregoing. 
Experiment  upon  animals  by  stimulation  is  of  no  direct  value  ;  it 
could  at  most  only  discover  the  cortical  regions  especially  related 
to  some  of  the  motions  of  the  eye  or  ear  and  their  surrounding 
parts.  Our  conclusions  from  the  method  of  extirpation  also  must 
always  be  somewhat  uncertain,  since  we  infer  the  sensations  of  the 
animal  only  by  interpreting  his  motions  into  terms  of  our  own  seK- 
consciousness.  It  is  not  strange,  then,  that  the  leading  experi- 
menters differ  irreconcilably  in  certain  of  their  conclusions.  There 
'  See  au  abstract  of  liis  results,  in  Brain,  July,  1884,  pp.  145  ff. 


286  CEREBRAL   FIELDS   OF   SENSATIOIT.  ' 

is  pretty  general  agreement  at  present,  however,  as  to  the  localiza* 
tion  of  sight  somewhere  in  the  occipital  lobe.  Hitzig  '  found  that 
the  removal  of  certain  gyri  in  the  posterior  lobes  of  the  dog  pro- 
duced blindness  of  the  opposite  eye,  combined  with  a  paralytic 
dilatation  of  its  pupil ;  stimulation  of  the  same  gyri  produced  con- 
traction of  the  pu j)il.  Ferrier  ^  claims  that  destruction  (by  cauter- 
ization chiefly)  of  the  gyrus  angularis  of  apes  produces  blindness  of 
the  opj)osite  eye,  and  this  loss  of  function  alone ;  stimulation  of  the 
same  region  causes  movements  of  the  eye.  He  therefore  considers 
this  convolution  as  pre-eminently  the  cortical  centre  of  sight.  But 
Munk,  after  numerous  experiments  upon  dogs,  and  some  upon 
monkeys,  locates  the  centre  of  sight  above  and  behind  the  place 
assigned  it  bj'  Ferrier — namely,  in  the  upper  and  hinder  part  of  the 
occipital  lobe  ;  the  gyrus  angularis,  on  the  contrary,  he  makes  the 
cortical  region  for  the  tactile  sensations  of  the  eye.  Munk's  ex- 
pei'iments  are  so  minute  in  carefulness,  and  his  conclusions  so 
based  upon  detailed  analysis  of  the  phenomena,  that  they  perhaps 
deserve  to  suggest  to  pathology  the  exact  form  in  which  to  put  its 
inquiry.  They  are,  undoubtedly,  excessive,  however,  in  the  refine- 
ment to  which  they  would  carry  the  principle  of  localization. 

§  20.  Munk  details  the  following  among  other  phenomena  which 
result  from  extirpating  the  region  marked  A^  (see  Fig.  85)  from  the 
brain  of  a  dog.  The  animal  thus  operated  upon  is  in  a  condition 
to  Avhich  the  name  of  "  psychical  blindness "  (Seelenhlindheit)  is 
given  ;  but  it  has  suffered  no  other  obvious  impairment  of  its  sen- 
sor}^ or  motor  functions.  By  "  jDsychical  blindness  "  is  meant  the 
inability  of  the  dog  to  form  those  visual  mental  images  or  ideas 
which  give  it  the  meaning  or  interpretation,  as  it  were,  of  its  visual 
imjDressions.  This  includes  the  loss  of  the  use  of  that  portion  of 
the  retina  which  is  necessary  for  distinct  vision,  and  of  the  immedi- 
ately surrounding  retinal  parts.  If  the  region  Aj  be  removed  from 
both  hemispheres  of  the  brain,  when  the  animal  has  recovered  from 
the  inflammatory  reaction,  it  will  still  move  about  freely,  guiding 
itself  by  sight  even  under  difficult  circumstances.  But  it  does  not 
recognize  by  sight  the  dish  from  which  it  has  been  accustomed  to 
take  food  or  water,  the  companions  with  which  it  has  formerly 
played,  the  man  who  has  been  its  keeper,  the  threatening  hand  or 

1  Centralb.  f.  d.  med.  Wissenschaft,  1874,  p.  548. 

2  The  Functions  of  the  Brain,  p.  164  f.  In  the  second  edition  (p.  271  f.) 
Ferrier  acknowledges  that  he  was  in  error  in  localizing  the  visual  centres  in 
this  gyrus  to  the  exclusion  of  the  occipital  lobes.  For  a  very  telling  criticism 
of  this  position  of  Ferrier,  see  Munk,  Ueber  d.  Functionen  d.  Grosshirurinde, 
p.  14  1 


THE   SIGHT- CEISTTEE   OF   MUNK.  287 

whip,  the  burning  coal  held  before  its  face.  It  still  retains  its  gen- 
eral intelligence  and  makes  constant  and  diligent  investigation  into 
the  objects  by  which  it  is  surrounded.  As  time  passes,  it  gradually 
learns  to  recognize  again  all  these  visual  objects.  The  more  com- 
plex and  infrequent  of  the  objects  are  the  last  in  the  process  of  re- 
covery to  receive  interpretation.  At  the  end  of  three  to  five  weeks 
after  the  operation,  the  injured  animal  may  be  said  to  have  recov- 
ered ;  its  restlessness  and  curiosity  have  subsided  in  proportion  to 
the  progress  made  in  the  knowledge  of  visual  impressions  ;  it  ^.s 
itself  at  last,  its  "  soul-blindness  "  having  departed.  It  may  be 
shown,  moreover,  that  this  recovery  consists  in  learning  anew  the 
meaning  of  visual  impressions ;  or,  in  other  words,  in  acquiring 
anew  the  stock  of  visual  ideas  that  has  been  blotted  out  of  the  ani- 
mal's mind  by  extirpating  the  cortical  centre  of  sight.  For  if  the 
dog  be  carefully  kept,  for  a  long  time,  fi'om  any  given  kind  of  ex- 
perience— for  example,  from  being  struck  with  a  Avhip  or  biu-ned 
with  a  coal — it  will  give  no  sign  of  "  psychical  sight "  in  relation  to 
these  particular  objects.  More  remarkable  still  is  the  fact  that, 
according  to  Munk,'  in  certain  cases,  after  the  extii'pation  of  Aj,  a 
single  visual  image  or  two — for  example,  the  motion  of  the  hand 
commanding  the  dog  to  hold  out  the  foot — may  be  retained.  Ex- 
tirpations of  the  cortical  surface  on  the  occipital  lobe  in  the  regions 
marked  A — that  is,  before,  beneath,  or  in  front  and  above,  the  sight- 
centre  A, — cause  disturbances  of  sight  in  a  less  degree.  Such  phe- 
nomena Munk  considers  explicable  by  the  hypothesis  that,  while  a 
large  part  of  the  area  of  the  occipital  lobe  is  the  seat  of  the  percep- 
tions (?)  of  sight,  the  visual  images  of  memory  are  especially  con- 
nected with  the  so-called  sight-centre  A^.  "When,  then,  all,  or  nearly 
all,  of  the  field  of  sight,  in  the  widest  sense,  is  extirpated  from  both 
hemispheres,  complete  and  permanent  "  soul-blindness "  results. 
The  cortical  projection-field  corresponding  to  the  entire  retinas  of 
both  eyes,  its  accumulations  of  old  visual  ideas,  and  capacity  for 
receiving  new  ones,  has  been  wiped  out. 

Munk  endeavors  to  establish  a  still  more  minute  differentiation 
of  function  in  the  cortical  field  of  sight  as  corresponding  to  the  ret- 
inal field  of  sight.  ^  Each  retina,  he  holds,  stands  for  the  most  part 
in  connection  with  the  visual  sphere  of  the  cortex  of  the  opposite  side 
of  the  brain  ;  only  a  small  part — namely,  the  extreme  lateral  por- 
tion of  the  retina — is  in  connection  with  the  cortical  sphere  of  the 
same  side.  This  lateral  poi-tion  of  the  retina  seems  to  be  of  differ- 
ent dimensions  in  different  races  of  dogs.     Further,  the  retina  ia 

'  Die  Functionen  d.  Grosshirnrinde,  pp.  23,  34,  119  f. 

*  See  the  "  Fuufte  Mittheiluug  "  of  his  Work,  as  cited  before. 


288  CEEEBEAL   FIELDS    OF   SENSATION. 

projected,  as  it  were,  on  the  cortical  field  of  vision  in  and  about  Aj, 
in  such  manner  that  its  lateral  area  corresponds  to  the  lateral  area 
of  the  cortical  sphere  on  the  same  side  ;  its  inner  area  to  the  median 
area  of  the  cortical  sphere  on  the  opposite  side. ;  its  upper  area  to 
the  front  area  of  the  cortical  sphere  on  the  opposite  side  ;  its  lower 
area  to  the  hinder  area  of  the  cortical  sphere  on  the  opjDosite  side. 

In  monkeys,  as  well  as  dogs,  Munk  finds  that  the  sight-centre  is 
not,  as  Ferrier  at  first  supposed,  the  gyrus  angularis,  but  rather  the 
convex  surface  of  the  i^osterior  lobes.  Small  circular  extirpations, 
of  not  more  than  two-fifths  or  three-fifths  of  an  inch  in  diameter, 
from  this  region  are  followed  by  disturbances  of  vision,  and  by  these 
alone.  If  the  whole  convex  surface  of  one  lobe  is  extirpated,  the 
animal  has  cortical  blindness  for  those  halves  of  both  retinas  that 
are  on  the  same  side  as  the  lesion.  If  the  convex  surfaces  of  both 
posterior  lobes  are  destroyed,  the  animal  becomes  entirely  blind ; 
no  restoration  of  cerebral  function  subsequently  takes  place,  unless 
some  considerable  parts  of  the  edges  on  the  upper  surface  of  at 
least  one  lobe  have  escaped  destruction.  The  cortical  projection- 
field  for  the  visual  impressions  of  the  monkey  differs  from  that  of 
the  dog  simply  in  having  the  lateral  part  of  the  retina,  which  cor- 
resjDonds  to  the  cortical  area  of  the  same  side,  much  more  extended. 
Accordingly,  extirpation  of  the  lateral  half  of  the  left  cortical  sight- 
centre,  and  of  the  median  half  of  the  right  cortical  sight-centre, 
produces  in  the  monkey  total  cortical  blindness  of  the  left  eye. 

§  21.  The  searching  examination  which  the  views  of  Munk  have 
received  has  resulted  in  throwing  doubt  over  some  of  his  alleged 
facts,  and  in  discrediting  several  most  important  points  in  his  hy- 
pothesis. This  is  true  especially  of  the  work  of  Lob  and  Luciani, 
both  of  whom  have  gone  thoroughly  over  the  ground  covered  by 
Munk  and  come  to  conclusions  dissenting  from  him.  The  former ' 
has  minutely  investigated  the  effects  of  destroying  Munk's  visual 
centre  A^,  and  even  his  entire  visual  sphere  in  the  case  of  dogs. 
He  finds,  contrary  to  Munk,  that  no  blindness  of  the  clear  spot  of 
vision  in  the  opposite  eye  is  produced  even  by  the  most  extensive 
lesion  of  this  area ;  that  losses  of  the  cortical  substance  in  the 
area  bordering  on  the  lateral  part  of  the  visual  sphere  {i.e.,  in 
Munk's  auditory  sphere)  also  produce  disturbances  of  vision  ;  that 
other  disturbances  of  motion  and  intelligence  also  follow  destruc- 
tion of  this  area  ;  and  that  disturbances  of  sight  may  follow  lesions 
in  other  than  the  occipital  lobes,  especially  in  the  frontal  lobes. 
This  last  conclusion  agrees  with  the  results  obtained  by  other  ob- 
sei"vers  (Ki'iwotorow,  Luciani  and  Tamburini,  and  especially  Goltz), 
'  See  articles  in  Pfliiger's  Arcliiv,  xxxiv. ,  pp.  67  ff. 


VIEWS    OF   LOB,    AND    OTHERS.  -  289 

and  must  be  accepted  as  correct.  The  more  permanent  disturb- 
ances which  undoubtedly  do  follow  injury  of  the  occipital  lobes 
are  thought  by  Lob  to  be  due  to  what  is  called  a  "  homonymous 
lateral  hemiamhlyopia  "  (or  weakness  of  the  corresponding  lateral 
half  of  the  eye)  on  the  opposite  side.  Munk's  whole  theory  of 
"  psychical  blindness  "  as  due  to  the  extirpation  of  visual  percep- 
tions and  images,  and  of  recovery  from  such  blindness  as  due  to 
special  education  of  the  animal  in  forming  new  mental  images,  is 
rejected  by  Lob. 

The  admirable  observations  of  Luciani  also  tend  to  disprove 
many  of  the  particular  conclusions  of  Munk,  while  at  the  same 
time  showing  how  relatively  important  are  the  occijntal  lobes  in  re- 
spect to  the  cerebral  and  psj'chical  elements  of  vision.  These  lobes, 
together  with  the  angular  gyrus,  are  in  a  peculiar  degree  the  re- 
gion on  which  the  animals  are  dependent  for  "  psychical "  vision 
— that  is,  for  "discernment  of  things,  and  a  right  judgment  con- 
cerning their  properties  and  their  nature,"  by  sight. 

The  foregoing  general  conclusions  from  experiment  with  the  ani- 
mals as  to  the  especial  importance  of  the  occipital  lobes  for  intelli- 
gent (or  "  psychical ")  vision  are,  on  the  whole,  in  accordance  with 
the  indications  from  human  pathology.  Even  Lob  testifies  that 
after  extirpating  part  of  the  occipital  lobes  he  has  never  observed 
a  ?7iere  motor  disturbance  without  one  of  vision  also  ;  whereas  after 
extirpating  part  of  the  parietal  lobes  he  has  never  observed  a  dis- 
turbance of  vision  loithout  a  motor  disturbance. 

§  22.  The  answer  of  pathology  to  the  question,  whether  the  cere- 
bral field  especially  connected  with  visual  sensations  and  ideas  is 
the  same  in  man  as  in  the  dog  and  the  monkey,  is  not  unambigu- 
ous. The  method  of  negative  cases,  according  to  Exner,' yields  no 
certain  results;  no  "absolute  field"  for  vision  can  as  yet  be  indi- 
cated on  the  cerebral  cortex.  The  methods  of  percentage  and  of 
positive  cases,  however,  point  clearly  to  the  occipital  lobe  as  the 
visual  field,  and  to  the  upper  end  of  the  first  gyrus  occipitalis  (01,  in 
Ecker's  charts ;  see  p.  276  f.)  as  its  most  intensive  portion.  Li  six  out 
of  seven  cases  of  disturbances  of  vision  due  to  cortical  lesion  the  seat 
of  the  lesion  was  here.  The  region  of  less  intensity  extends  over 
both  the  first  and  second  occipital  convolutions,  the  cuneus,  and 
the  adjacent  part  of  the  lobulus  quadratus.  Confirmatory  evidence 
may  be  found  in  the  cases  of  several  persons  for  a  long  time  blind, 
whose  brains  have  been  found  on  post-mortem  to  be  atrophied 
above  the  place  where  the  parieto-occipital  fissure  emerges  from 
the  median  surface  upon  the  convex  surface  of  the  occipital  lobe. 
'  Untersucliungen  iiber  d.  Localisation,  etc.,  p.  60. 
19 


290  CEREBRAL    FIELDS    OF   SENSATION. 

It  should  be  said,  on  the  other  hand,  that  lesions  of  the  occipital 
lobes  are  very  frequently  latent,  and  that  extensive  injuries  of  this 
cortical  field  in  man  are  recorded  which  v^^ere  followed  by  no 
marked  disturbance  of  sight. 

§  23.  Histology  also  has  some  evidence  to  contribute  regarding 
the  nervous  connections  of  the  retinas  of  the  eyes  with  the  cerebral 
cortex.  The  amount  of  crossing  which  the  fibres  of  the  ojDtic  nerve 
undergo  in  the  optic  chiasm  has  been  the  subject  of  much  debate. 
It  undoubtedly  differs  in  different  animals,  and  depends  uj^on  the 
structures  of  both  retina  and  brain,  and  upon  the  relations  of  the 
two.  The  researches  of  von  Gudden  '  and  others  have  tended  to 
show  that  each  optic  nerve  contains  both  a  bundle  of  nerve-fibres 
that  is  crossed  and  one  that  is  uncrossed,  in  the  optic  chiasm  or 
beyond  it,  towai'd  the  cerebral  connections  of  the  nerve  ;  and  that 
the  former  bundle  increases  and  the  latter  diminishes  in  size,  on 
the  whole,  in  the  higher  orders  of  animals  as  compared  with  the 
lower.  Biesiadeclii  and  others  claim,  on  the  contrary',  that  there 
is  total  decussation  of  the  otitic  nerves  in  the  monkey  and  in  man, 
as  well  as  the  lower  animals.  Charcot  °  has  propounded  a  yet  more 
elaborate  scheme  of  decussation.  In  the  case  of  man  there  is  still 
doubt,  therefore,  how  far — if  at  all — the  retina  of  each  eye  is  repre- 
sented on  the  cortical  surface  of  both  hemispheres  of  the  brain. 
That  the  cortical  region  especially  concerned  in  the  sensations, 
perceptions,  and  images  of  sight  is  in  the  occipital  lobe,  and  es- 
pecially on  its  upper  convex  surface,  is  a  highly  probable  conject- 
ure. But  for  the  settlement  of  further  details  we  must  await  the 
development  of  the  evidence.  In  the  work  of  this  develoj^ment, 
experiment  with  aiaimals  can  only  suggest  the  question  which  a 
more  careful  collation  of  a  growing  number  of  cases  in  human 
pathology  will  perhaps  finally  answer  ;  meanwhile  the  evidence  of 
histology  may  be  used  to  confirm  or  modify  the  conclusions  estab- 
lished, more  or  less  conjecturally,  on  the  basis  of  pathology.^ 

§  24.  The  localization  of  other  sensory  functions  in  so-called 
"  fields  "  or  "  centres  "  on  the  hemispheres  of  man's  brain — of  hear- 
ing, taste,  and  smell — is  even  more  doubtful.  Little  confidence  can 
be  placed  in  any  conjectures  thus  far  put  forwai'd.  The  tempta- 
tion is  naturally  strong  to  suspect  that  those  regions  of  the  cortex 
unoccupied  by  such  motor  and  sensory  functions  as  we  are  able  to 

'  Grafe's  Archiv  f ,  Ophthalmologie,  1874,  Abth.  ii. ;  1875,  Abth.  iii. ;  1879, 
Abth.  i. 

-  Le  Progri's  Medical,  August,  1875. 

■'For  a  further  description  of  plienomena  and  cases,  and  for  a  defence  of  his 
own  views,  see  Ferrier,  The  Localization  of  Cerebral  Disease,  pp.  110  fiE. 


CElVfTEES   OF   SMELL   AND   TASTE.  291 

locate  should  have  the  other  mental  phenomena  assigned  to  them. 
In  this  way  the  entire  brain  appears  to  be  made  of  some  definite 
value  and  use.  Convolutions  which  are  located  where  they  are 
unapproachable  for  purposes  of  experiment,  and  in  which  compar- 
atively few  cases  of  lesion  occur,  are  peculiarly  provocative  of  con- 
jecture. In  such  Jields  of  the  cerebral  cortex,  theories  of  localiza- 
tion may  roam  at  will.  The  auditor^'  centre  is  assigned  by  Terrier  ' 
to  the  superior  temporo-sphenoidal  convolution  ;  but  the  evidence 
adduced  in  proof — such  as  the  pricking-ujD  of  the  animal's  ears, 
etc, — is  highly  unsatisfactory.  The  same  centre  is  located  by 
Munk  '^  at  the  region  Bl,  for  its  greatest  intensity,  and  with  less 
intensity  in  the  adjacent  regions  marked  B  ;  but  since  the  entire 
region  on  both  hemispheres  must  be  extirpated  (an  almost  certain- 
ly deadly  operation)  in  order  that  the  animal  may  become  wholly 
"  soul-deaf,"  and  since  we  have  no  sure  means  for  ascertaininsr 
precisely  to  what  deficiency  we  should  ascribe  the  failure  of  the 
animal  to  respond  intelligently  to  sounds,  Munk's  experimental 
proof  is  likewise  unconvincing.  Luciani,  with  much  more  proba- 
bility, considers  the  "  auditory  sphere  "  to  extend  over  the  whole 
cortical  area  of  the  temporo-sphenoidal  lobe,  and  probably  also  the 
cormi  ammonis. 

The  centres  of  smell  and  taste  are  located  by  Ferrier  close  to- 
gether in  the  subicidum  and  neighboring  parts  of  the  lower  temporo- 
sphenoidal  convolutions  ;  the  centre  of  touch  in  the  gyrus  hijjpo- 
campi  and  hippocampus  major.  Munk,^  however,  regards  these 
centres  of  Fei'rier  as  "  phantasms."  He  is  strongly  inclined,  on  the 
basis  chiefly  of  one  well-differentiated  case,  to  localize  smell  in  the 
gyrus  JdiopocampL  It  is  difficult  to  see  how  anything  sufficiently 
definite  for  scientific  purposes  can  be  known  as  to  distui-bances  of 
taste  in  a  dog  or  a  monkey.  No  adequate  evidence  is  j)rocurable  as 
yet  for  an  induction  from  human  pathological  cases  in  regard  to 
the  cortical  fields  of  any  of  these  so-called  lower  senses. 

§  25.  To  the  foregoing  remark  a  possible  exception  must  be 
allowed  for  the  sense  of  hearing.  In.  this  connection  belongs  the 
noteworthy  localization  of  the  cerebral  functions  concerned  in  the 
utterance  and  interpretation  of  articulate  speech.  The  various  de- 
ficiencies in  the  power  of  producing  and  interpreting  articulate 
sounds,  whether  as  spoken  or  written,  which  are  due  to  lesions  of 
the  cerebral  cortex,  may  be  grouped  together  under  the  general 

'  The  Functions  of  the  Brain,  p.  171  f.  ;  comp.  The  Localization  of  Cerebral 
Disease    p.  132  f. 

-  Ueber  d.  Functionen  d.  Grosshirnrinde,  p.  23  f .  ;  40  f. 
3  Ibid.,  p.  129. 


292  DISTURBAISrCES   OF   SPEECH. 

term  "aphasia."  For  about  a  decade  previous  to  the  discoveries 
of  Fritsch  and  Hitzig,  in  1870,  the  facts  Avhich  seemed  definitely  to 
connect  the  loss  of  speech  with  a  certain  region  of  the  left  cere- 
bral hemisphere  were  nearly  all  to  which  any  advocate  of  the  local- 
ization of  cerebral  function  could  confidently  appeal  in  behalf  of 
his  theory.  As  long  ago  as  1825,  Boillaud  located  the  articulation 
of  words  in  the  frontal  lobes.  Subsequently  (1836)  M.  Dax  main- 
tained the  proposition  that  "  lesions  of  the  left  half  of  the  enceph- 
alon  are  coincident  with  forgetfulness  of ^the  symbols  of  thought." 

In  treatises  of  the  years  1861-1865,  Broca  first  announced  the 
substantially  true  discovery  that  the  gyrus  frontalis  inferior  on  the 
left  side  of  the  cerebrum  is  especially  concerned  in  using  the  pow- 
er of  siDcech.  This  circumstance  he  connected  with  the  fact  that 
men  generally  use  the  left  hemisphere  more  than  the  right  for  the 
expression  of  thought  with  the  I'ight  hand  and  arm,  whether  in 
writing  or  in  the  mechanical  arts.  The  literal  meaning  of  the 
statements  made  hj  Broca — such  as  that  this  part  of  the  brain  is 
"the  seat  of  the  faculty  of  articulate  language  "  ' — is,  however,  not 
simply  inappropriate  to  the  facts  ;  it  is  even  absurd.  There  is  no 
one  "  faculty  "  of  language  which  can,  in  any  possible  meaning  of 
the  word,  be  regarded  as  having  its  "seat  "  or  locality  confined  to 
some  particular  region  of  the  brain.  Speech  involves,  in  a  very 
complicated  and  large  way,  all  the  faculties  ;  strictly  speaking,  then, 
it  cannot  be  located,  with  all  its  attendant  operations  of  self-con- 
scious, rational  mind,  in  any  one  cerebral  area.  But  that  the 
phenomena  of  aphasia  show  some  special  connection  of  certain 
cerebral  centres  with  the  complex  process  of  apprehending  and  ex- 
pressing articulate  language,  seems  entitled  to  credit  as  an  induc- 
tion based  upon  a  wide  range  of  facts.  Of  course,  in  this  particu- 
lar attempt  at  localization  of  function,  no  real  help  can  be  derived 
from  experiments  upon  the  lower  animals. 

§  26.  The  jDhenomena  of  various  classes,  among  which  the  truly 
aphasic  cases  must  be  discriminated,  vary  all  the  way  from  those 
resembling  the  results  of  momentary  inattention — such  as  that  of 
the  German  professor  who  certified  in  writing,  "A.  B.  has  attended 
my  remarkable  lectures  in  chemistry  with  inorganic  assiduity  "■ — to 
the  impairment  and  utter  loss  of  speech  in  progressive  paralysis 
with  dementia."     A  few  of  the  more  curious  and  instructive  in- 

'  Sur  le  siege  de  la  faculte  du  langage  articnle,  etc.,  Bull,  de  la  Soc.  anat.. 
August,  1861  ;  Du  siege  de  la  faculte  du  langage  articule  dans  I'hemisphere 
gauche  du  cerveau.  Bull,  de  la  Soc.  d'anthropol. ,  June,  18(55. 

'For  the  whole  subject,  see  the  great  monograph  of  Kussraaul,  in  Ziemssen'a 
Cyclopaedia,  xiv.,  pp.  581-875. 


THE   KINDS   OF   APHASIA.  293 

stances  furnish  facts  like  the  following  :  The  aphasic  patient  may 
be  entirely  speechless,  and  yet  understand  what  is  said  to  him,  and 
be  able  to  write  his  wishes  down  on  paper.  Some  thus  afflicted  re- 
tain the  power  to  pronounce  words  of  one  syllable,  but  are  obliged 
to  resort  to  writing  in  order  to  communicate  anything  fm-ther.  Oth- 
ers possess  a  small  stock  of  words,  which  they  make  more  serviceable 
with  expressive  gestures.  Others,  still,  are  simply  able  to  speak  "  a 
few  senseless,  and  often  very  extraordinary,  syllables  and  words." 

Among  the  surprising  phenomena  of  the  disease  of  aphasia, 
none  are  perhaps  more  so  than  those  occasioned  by  the  ability 
to  utter  certain  syllables  or  words,  when  accompanied  by  an  utter 
inability  to  put  the  same  letters  into  slightly  different  combination. 
One  patient,  who  could  say  "Bonjour,  monsieur,"  tolerably  well, 
could  not  pronounce  the  word  "bonbon"  at  all.  Another,  whose 
vocabulary  was  almost  entirely  limited  to  the  meaningless  syllables, 
"  cousisi,"  was  quite  unable  to  utter  either  "  coucon  "  or  "sisi." 
The  celebrated  case  of  the  aphasic  Le  Long,  reported  by  Broca, 
was  that  of  a  man  confined  to  five  words  for  his  entire  vocabulary. 
These  words  were,  "  oui,  non,  tois  instead  of  trois,  toujours,  and 
Le  Lo  instead  of  Le  Long."  The  first  two  and  the  last  were  used 
with  their  appropriate  meaning;  "tois"  indicated  all  ideas  of 
number  whatever  ;  and  "  toujours"  was  the  word  used  when  the 
patient  could  not  express  his  meaning  by  gestures  and  the  other 
four  words.  It  appears,  then,  that  Le  Long  could  pronounce  the 
r  in  "  toujours,"  but  not  in  "  trois,"  and  the  nasal  sound  in  "  non," 
but  not  in  his  own  name.  In  another  class  of  cases,  the  aphasic 
person  can  utter  only  a  few  or  no  words  spontaneously  and  cor- 
rectly, but  can  repeat  and  write  without  difficulty  words  that  are 
spoken  before  him.  Such  inability  is  sometimes  called  "simple 
aphasia  of  recollection."  Different  classes  of  words,  as  a  rule,  slip 
fi-om  the  memory  in  succession,  as  it  were.  Proper  names  are 
most  frequently  forgotten  ;  then  substantives  generally,  and  some- 
times verbs,  adjectives,  pronouns,  and  all  other  parts  of  speech. 
"The  more  concrete  the  idea,"  says  Kussmaul,'  "the  more  readily 
the  word  to  designate  it  is  forgotten,  when  the  memory  fails." 
Many  cases  of  disease  occur  where  the  patient  has  lost  the  power 
mentally  to  find  the  appropriate  words,  although  his  power  of  ar- 
ticulation is  unimpaired.  Such  disturbances  of  speech  may,  or  may 
not,  be  accompanied  by  a  corresponding  impairment  of  general  in- 
telligence. This  complication  increases  the  difficulty  of  studying 
the  phases  of  this  disease. 

Aphasia  may  also  be  accompanied  by  so-called  "word-deafness" 
'  Ziemsseu's  Cyclopaedia,  xiv. ,  p.  759. 


294:  DISTURBANCES   OF   SPEECH. 

and  "word-blindness."  Persons  thus  afllicted  hear  words  as  con- 
fused nmrmurings,  or  see  them  as  bluri'ed  images.  The  individ- 
ual letters  may  be  intelligently  heard  or  read,  but  their  combina- 
tion has  become  unintelligible.  The  same  thing  sometimes  happens 
with  figures  ;  as  in  the  case  of  the  accountant  who  could  read  the 
sum  7G6,  figure  for  figure,  but  did  not  know  what  the  figure  7 
meant  as  placed  before  the  two  6's.  At  other  times  the  disturb- 
ance of  speech  takes  the  form  of  grammatical  ataxy,  as  it  were,  or 
of  verbal  delirium — a  medley  of  words,  partly  in  themselves  signifi- 
cant and  partly  unmeaning. 

The  agraphia,  or  inability  to  express  thought  in  written  language, 
which  not  infrequently  accompanies  aphasia,  may  be  incomplete, 
or  absolute  and  literal.  Some  patients,  who  have  formerly  been 
highly  cultivated,  become  unable  to  produce  a  single  letter  with 
the  pen.  Others  can  write  long  rows  of  letters,  but  arrange  them 
for  the  most  pai't  in  meaningless  fashion,  with  an  intelligible  word 
occurring  here  and  there.  In  brief,  the  phenomena  more  or  less 
closely  connected  with  the  disturbance  called  aphasia  are  exceed- 
ingly complex  and  various. 

§  27.  In  the  effort  to  classify  so  many  complicated  facts,  and  to 
distinguish  among  them  such  as  are  of  truly  cerebral  origin,  Ex- 
ner'  makes  the  following  distinctions:  First,  there  are  cases 
where  the  understanding  of  the  words  is  affected  ;  and  such  loss 
may  constitute  the  chief  or  the  entire  part  of  the  aphasia.  The 
patient  can  then  hear  and  articulate,  but  the  "acoustic  image"  of 
the  word  as  the  symbol  of  an  idea  has  jDcrished.  In  a  second  form 
of  aphasia,  the  inability  concerns  the  clothing  of  the  result  of 
thought  (the  idea)  in  words — whether  for  purposes  of  spoken  or  of 
written  expression.  In  most  such  cases  it  is  simjDly  the  appro- 
priate word  which  is  forgotten.  In  the  third  class  of  cases,  the 
aphasic  person  can  foi'm  the  idea  and  select  the  word  approj)i'iate 
to  express  it,  but  cannot  bring  about  those  processes  of  central  in- 
nervation which  are  necessary  to  initiate  the  expression.  All  these 
three  forms  may  combine  variously,  and  all  may  be  connected  with 
disturbances  of  speech  which  are  not  to  be  localized  in  the  cerebral 
cortex,  but  which  have  their  origin  at  some  point  in  the  extra-cor- 
tical nerve-tracts  concerned  in  speech.  The  very  elaborate  analysis 
of  Kussmaul  leads  him  to  make  the  following  statement:  "All 
disturbances  of  speech  can  be  brought  under  two  great  classes^ 
according  as  the  connection  between  the  conception  and  the  word 
is  impeded  in  the  direction  from  the  former  to  the  latter  or,  vice 
versa,  from  the  latter  to  the  former.  When  the  first  happens,  the 
'  In  Hermaun's  Handb.  d.  Physiol. ,  II.,  ii.,  p.  343  f. 


CORTICAL   AREAS   OF   APHASIA.  295 

expression  suffers;  when  the  second,  the  understanding."  By  the 
1  ist  word,  however,  we  must  naean  the  "  understanding  "  as  apphed 
especially  to  articulate  speech.  For  aphasic  persons  are  often  very 
intelligent  in  carrying  on  the  trains  of  thought  necessary  to  suc- 
cess in  games  of  skill,  or  in  the  expression  of  feeling  in  music  ;  and 
if  we  accept,  even  with  considerable  allowances,  the  intelligent 
testimony  of  Lordat  concerning  his  own  mental  condition  when 
aphasic,  they  sometimes  exercise  the  mind  in  abstract  reasoning 
of  a  high  order,  even  when  unable  to  recall  a  single  word  appro- 
priate for  the  expression  of  their  thoughts. 

In  all  true  aphasia,  then,  the  connection  between  ideas  and  ar- 
ticulate language  is  interrupted  within  the  cerebral  cortex.  Is  it 
possible  to  indicate  any  region  of  this  cortex,  lesions  in  which  are 
regularly  accompanied  by  aphasic  symptoms  ?  or,  in  other  woi'ds, 
Can  the  function  of  articulate  speech,  so  far  as  this  consists  in  the 
ability  to  apprehend  and  successfully  to  will  its  acoustic  and  visual 
symbols,  be  localized  in  the  cerebral  hemispheres  ?  In  answer  to 
this  question  it  must  be  admitted  that  no  absolute  field  for  aphasia 
can  be  pointed  out ;  that  is,  besides  the  region  where  lesions  are 
connected  in  by  far  the  greater  number  of  cases  with  aphasic  dis- 
turbances, other  regions  of  the  cerebral  hemispheres  only  some- 
limes  thus  connected  may  be  pointed  out. 

§  28.  In  a  large  percentage  of  cases  of  disturbance  of  speech  due 
to  cerebral  lesions,  the  posterior  third  of  the  third  frontal  convolu- 
tion and  the  other  regions  bordering  on  the  fissure  of  Sylvius 
(island  of  Eeil,  and  immediately  adjacent  parts  of  the  parietal  and 
temporal  lobes)  are  the  seat  of  the  lesions.  Aphasia  is  far  more 
frequently  due  to  changes  in  the  left  than  in  the  right  hemisphere 
of  the  brain.  Dr.  Seguin,  out  of  260  cases,  calculated  the  propor- 
tion of  aphasias  due  to  lesions  on  the  left  side,  as  compared  with 
those  due  to  lesions  on  the  right,  to  be  as  243  :  17  or  14.3  : 1.  Such 
disparity  is  far  too  great  to  be  attributed  to  the  comparative  fre- 
quency with  which  the  left  hemisphere  in  general  is  the  seat  of 
lesions.  In  Exner's '  collection  of  cases,  out  of  81  lesions  resulting 
in  aphasia,  all  but  one  were  on  the  left  hemisphere  (in  three  cases, 
however,  the  right  was  also  involved),  and  in  that  one  the  trouble 
was  only  temporary.  Such  facts  have  led  to  the  theory  that,  in  all 
but  left-handed  men,  speech,  like  other  motor  functions,  is  chiefly 
left-brained  ;  remarkable  cases  of  left-handed  people  who  have  be- 
come aphasic  through  lesions  on  the  right  hemisphere  are  actually 
recorded.^ 

'  Functionen  in  d.  Grossliirnrinde,  p   51  f. 
^  See  Kussmaul  and  his  citations,  p.  739  f. 


296  DISTURBANCES    OF    SPEECH. 

Of  the  left  hemisphere,  the  gyruii  centralis  anterior  and  the 
adjacent  convokitions  of  the  frontal  lobe,  but  especially  the  pos- 
terior part  of  the  third  (lower)  convolution,  have  much  the  highest 
intensity  as  seats  of  aphasia  lesions.  In  53  carefully  collected 
cases  by  Lohmeyer,'  60  were  on  the  left  hemisphere,  24  in  the 
lower  frontal  convolution,  34  in  this  convolution  and  neighboi-ing 
parts,  13  in  the  island  and  adjacent  parts,  6  in  the  island  alone. 
Exner's  collection,  however,  did  not  show  that  the  "intensity"  of 
the  lower  is  any  greater  than  that  of  the  middle  frontal  convolution, 
or  of  the  two  upper  temporal  convolutions.  This  collection  con- 
tained, moreover,  five  cases  in  which  lesions  were  seated  in  the 
lower  left  frontal  convolution  loithout  any  resulting  aphasia.  Exner 
therefore  justly  concludes  that  the  "  cortical  field  "  of  speech,  like 
the  corresponding  fields  of  all  the  motor  functions,  is  really  much 
more  extended  than  has  generally  been  supposed.  He  is  himself, 
nevertheless,  inclined  to  localize,  yet  more  definitely,  so-called 
"ataxic  aphasia"  in  the  third  frontal  convolution,  "word-deaf- 
ness" in  the  middle  gyrus  temporalis,  and  agraphia  in  the  lower  and 
front  part  of  the  parietal  lobe ;  that  is,  in  the  neighborhood  of 
the  motor  region  for  the  upper  extremities.  So  specific  localiza- 
tion can  hardly,  however,  be  safely  based  on  the  restricted  number 
of  cases  which  Exner  considered. 

Lohmeyer  gives  2  cases  of  aphasia  following  lesions  in  the  an- 
terior portion  of  the  frontal,  3  in  the  parietal,  and  4  in  the  occipital 
lobe,  Exner  gives  3  cases  in  which  the  central  convolutions  were 
alone  the  seat  of  disease  ;  2  in  which  the  temporal  and  parietal 
lobes  were  alone  affected  ;  1  in  which  the  only  lesion  was  in  the  oc- 
cipital lobe.  In  the  only  sense  in  which  the  brain  can  be  spoken 
of  as  the  "  seat  of  the  faculty  of  articulate  language,"  we  must  ad- 
mit that  the  evidence  confirms  the  following  assumption  of  Kuss- 
maul :  "  It  is,  a  liriori,  probable  that  an  enormous  association-tract 
in  the  cortex  has  been  assigned  to  speech,  even  though  the  key- 
board of  sound  may  be  confined  to  the  anterior  cortical  regions." 

§  29.  The  moi'e  ardent  and  positive  advocates  of  the  theory 
of  locally  specific  cerebral  functions  find  it  exceedingly  difiicult  to 
refrain  from  seating  general  intelligence,  or  the  powers  of  percep- 
tion, memor}^,  comparison,  etc.,  as  applied  to  all  the  objects  of 
cognition,  in  some  particular  so-called  "field  "or  "area  "of  the 
brain.  At  present  the  frontal  lobes  offer  themselves  as  the  most 
convenient  region  for  such  pre-empting  of  the  cerebral  domain. 
The  general  propriety  of  considering  the  connection  which  un- 
doubtedly exists  between  the  central  nervous  mechanism  and  men- 
'  Arcliiv  f.  Klin.  Cliirurgie,  XIII.,  p.  309,  as  cited  in  Kussmaul. 


IMPAIEMENT    OF   I]SrTELLIGE]S"CE.  297 

tal  phenomena,  under  any  spatial  terms  whatever,  will  occupy  our 
attention  later  on.  It  is  enough  at  present  to  say  that  the  experi- 
mental and  pathological  evidence  do  not  warrant  us  in  assigning 
such  pre-eminence  to  the  frontal  lobes.  Extensive  lesions  may  oc- 
cur in  these  lobes  with  little  or  no  diminution  of  so-called  general 
intelligence.  On  the  other  hand,  small  lesions  in  other  regions  of 
the  brain  are  not  infrequently  productive  of  comparatively  profound 
mental  derangement  or  loss  of  function.  Moreover,  lesions  localized 
in  those  areas  of  the  cerebral  cortex  which  have  thus  far  been  con- 
sidered—namely, the  parietal,  occipital,  and  temporo-sphenoidal 
lobes— are,  of  necessity,  connected  with  more  or  less  impairment 
of  intelligence. 

There  can  be  no  doubt  that  the  mental  processes  which  we  describe 
by  the  word  "intelligence  "  are  all  closely  related  to  the  basic  sensory 
and  motor  activities  that  are  chiefly  localized  elsewhere  than  in  the 
frontal  lobes.  An  animal  that  is  "  soul-deaf  "  or  "  soul-blind  "  has, 
so  far  forth,  an  impaired  intelhgence.  The  same  thing  is  eminently 
true  of  the  man  afflicted  with  aphasia  in  any  of  its  severer  forms. 
The  loss  of  intelligence  is  not  necessarily  (or  even  probably)  due  to 
the  partial  destruction  of  that  functioning  of  the  hemispheres  in 
general  which  results  in  intelligence  ;  it  is  rather  due  to  the  fact 
that  the  support  which  all  ideation  receives  from  the  audible  and 
visible  symbols  of  the  idea— whether  chiefly  as  respects  its  forma- 
tion or  as  respects  its  expression — has  become  impossible.  The 
impairment  of  any  considerable  area  of  tactile  sensations,  especially 
as  localized  in  those  parts  of  the  body  which  are  most  used  in  per- 
ception through  such  sensations  {e.g.,  the  hand),  also  occasions  a 
certain  loss  of  intelligence.  The  restrictions  which  cerebral  disease 
introduces  into  the  number  and  nicety  of  the  sensory  and  motor 
functions  are,  of  course,  much  less  important  when  they  come  upon 
minds  already /»rni67ierf,  as  we  say,  "  with  a  stock  of  ideas."  Still, 
even  in  such  cases  a  basis  of  sensations  and  volitions  constantly 
underlies,  as  it  were,  all  the  higher  and  pre-eminently  intellectual 
mental  processes. 

§  30.  In  spite  of  the  evidence  adduced,  a  few  experimenters  still 
either  wholly  reject  the  principle  of  the  localization  of  cerebral 
function,  or  else  urge  arguments  against  carrying  it  out  even  with 
the  limitations  which  the  foregoing  conclusions  have  observed. 
Among  such  experimenters  the  most  prominent  is  perhajDS  Goltz. ' 
The  method  of  extirpation  practised  by  Goltz  was  that  of  wash- 
ing away  the  substance  of  the  cerebrum  by  streams  of  water  sent 

'  See  especially  liis  treatises  as  collected  in  the  book,  Ueber  d.  Verriclitungen 
d.  Grosshiriis,  Boun,  1881 ;  and  Pfliiger's  Arcbiv  for  1876,  1877,  and  1879. 


298  SUMMA-ET   OF   RESULTS. 

through  orifices  broken  at  selected  places  in  the  skulls  of  dogs. 
This  metbocl  has  the  advantage  of  saving  bleeding  ;  it  has  the  dis- 
advantage of  not  definitely  localizing  the  injuiy.  Its  author  has 
applied  it  with  great  care  and  skill  to  a  large  number  of  animals, 
many  of  which  he  has  succeeded  in  keeping  alive  for  months,  even 
after  the  removal  of  considerable  areas  from  both  hemispheres 
(in  one  instance  tbe  brain-substance,  calculated  to  have  weighed 
originall}'  93  grammes,  had  been  reduced  to  13).  The  principal 
conclusions  drawn  from  his  expei'iments  by  Goltz  are  adverse 
to  the  theories  of  localization  held  by  Ferrier,  Munk,  Luciani,  and 
others. 

Goltz's  conclusions  may  be  summarized  as  follows.  No  impair- 
ment of  intelligence  follows  the  loss  of  a  large  amount  of  cortical 
substance  from  one  side  of  the  brain  ;  but  loss  of  any  considerable 
amount  of  substance  from  both  sides — whether  in  the  frontal, 
posterior,  or  temporal  lobes — produces  a  permanent  impairment  of 
all  the  functions,  which  corresponds  in  a  general  way  to  the  amount 
of  the  loss.  Every  sense,  and  the  inteUigence  of  every  sense,  is 
thus  weakened  ;  for  tlie  cerebral  elements  of  sense  are  impaired  or 
destroyed  [Hirnsehschwache,  etc.).  For  example,  a  dog  which  has 
been  trained  to  give  his  paw  on  command  loses  the  power  to  do  so 
in  consequence  of  such  loss  of  brain-substance,  and  never  regains  it. 
It  is  not  possible,  by  extirpating  any  amount  of  the  substance  of 
the  cortex  on  either  side  or  on  both  sides,  to  produce  a  permanent 
laming  of  any  muscle  of  the  body,  or  a  total  loss  of  sensibility  in 
any  of  its  parts.  It  is,  however,  possible,  according  to  Goltz,  by 
repeated  removal  of  the  cerebral  substance  on  both  sides,  gi-adually 
to  reduce  an  animal  to  a  condition  of  almost  complete  idiocy — to 
an  elaborate  eating,  drinking,  and  walking  "reflex-machine."  The 
removal  of  as  much  as  4  grammes  from  each  hemisphere  produces, 
as  he  calculates,  a  considerable  degree  of  idiocy.  No  part  of  the 
cortex  of  the  brain  can,  then,  be  called  the  exclusive  organ  or  centre 
of  intelligence  or  feeling  ;  but  the  psychical  functions  of  sensation, 
volition,  ideation,  and  thought  are  connected  with  all  of  its  parts. 
The  quantity  of  the  cerebral  substance  i-emoved  determines  the 
amount  of  the  general  impairment  of  mental  powers,  instead  of  the 
locality  from  which  the  removal  is  made  fixing  the  quality  of  mental 
impairment. 

It  must  be  admitted  that  the  facts  discovered  by  Goltz,  and  the 

conclusions  which  he  reaches,  seem  at  first  strongly  opposed  to  all 

localization  of  cerebral  function.     But  they  are  not  really  so  ;  nor 

is  it  quite  coi-rect  even  to  say,  as  Foster  '  does,  that  Goltz's  results 

'  A  Text-book  of  Physiology,  p.  649.     New  York,  1880. 


THE  VIEWS   OF   GOLTZ.  299 

are  "absolutely  opposed"  to  tliose  of  Munk.  In  fact,  Goltz'  him- 
self asserts  that  destruction  of  the  parietal  lobes  produces  a  greater 
permanent  disturbance  of  feeling,  and  destruction  of  the  occipital 
lobes  a  greater  permanent  disturbance  of  sight.  In  general,  an 
animal  operated  upon  in  the  two  hind-quarters  of  the  cerebrum  is 
more  stupid  than  one  which  has  suffered  loss  of  the  fore-quarters ; 
the  former  is  duller  of  sight,  hearing,  smell,  and  taste ;  the  latter  is 
duller  in  respect  to  skin-sensations.  The  effect  of  injury  to  the 
posterior  parts  of  the  brain  is  therefore  much  more  marked  in  de- 
pressing the  intelligence  of  the  animal  (as  shown  in  sense-percep- 
tion). Moreover,  Goltz  ^  claims  that  he  has  never  rejected  the 
possibility  of  a  localization  of  the  functions  of  the  brain.  He  con- 
firms ^  the  conclusions  of  Fritsch  and  Hitzig,  by  saying  that  he  has 
often  seen  mechanical  excitation  of  the  parietal  lobes  j^roduce  mo- 
tions in  the  limbs  of  the  opposite  side.  His  facts  and  arguments 
are  rather  directed  against  tliat  form  of  the  hypothesis  of  localiza- 
tion which  seats  the  different  functions  in  small  circumscribed 
areas  ^  and  then,  w^hen  forced  by  facts,  conceives  of  them  as  also  ca- 
pable of  hopping  about  from  one  of  these  areas  to  another,  like  a 
bird  from  twig  to  twig  in  the  branches  of  a  tree.  Furthermore,  a 
detailed  comparison  of  the  experiments  of  Goltz  with  those  even 
of  Munk  shows  that  the  results  of  the  two  are  in  the  main  recon- 
cilable ;  if  only  it  be  remembered  that  the  former  has  not  always 
precisely  defined  the  areas  of  brain-substance  removed,  nor  suffi- 
ciently taken  into  account  the  undoubted  results  obtained  by  others 
from  definitely  circumscribed  lesions ;  and  that  the  latter  has,  cer- 
tainly, in  many  cases  been  more  precise  and  confident  than  a  fair 
view  of  all  the  facts  will  warrant. 

§  31.  Three  principles  may  be  laid  down  as  summing  up  the 
results  reached  by  inference  upon  the  basis  of  experiment  with 
respect  to  the  localization  of  function  in  the  cerebral  cortex. '"  The 
first  principle  is  to  be  accepted  in  the  form  of  a  general  postulate 
derived  from  a  study  of  the  other  parts  of  the  nervous  system,  and 
confirmed  on  attempting  to  apply  it  to  the  cerebral  hemispheres. 
It  may  be  stated  as  follows  :  the  different  elementally  parts  of  the 
nervous  system  are  all  capable  of  performing  its  different  sj^ecific 
functions  when,  and  only  when,  they  have  been  brought  into  the 
proper  connections  and  have  been  exercised  in  the  performance  of 

'  Verrichtungen  d.  Grossliirns,  pp.  114  f.  and  loO  f. ;  and  art.  in  Pfliigers 
Archiv.  xxxiv.,  pp   450  ff. 

^  Verrichtungen  d.  Grossliirns,  p.  163.     ^Ibid.,  p.  165.     *Ibid..  p.  169. 

'  Compare  the  five  general  laws  o£  central  functions  given  by  Wundt, 
Grundzuge  d.  pliysiolog.  Psycliologie,    i.,  p.  224  f. 


300  sujVimakt  of  results. 

tliose  functions.  This  principle  includes  two  important  laws  which, 
we  know,  hold  good  throughout  the  whole  nervous  mechanism,  and 
which  he  at  the  physical  basis  of  important  psychical  facts  and  laws ; 
they  are  the  law  of  Specific  Energy  and  the  law  of  Habit.  Different 
combinations  of  the  elementary  parts  of  the  nervous  system,  form- 
ing composite  parts  or  organs,  have  different  values  and  functions 
in  the  general  economy  of  the  system.  Every  nerve-fibre,  every  ele- 
ment of  an  end-organ,  or  of  a  central  organ,  may  be  said  to  have  a 
specific  function,  and  to  discharge  that  function  in  the  exercise  of 
a  specific  energy.  As  to  how  far  the  capacity  for  this  specific  energy 
is  dependent  upon  the  specific  molecular  structure  of  the  element- 
ary parts,  we  are  only  able  to  conjecture  ;  but  about  its  depend- 
ence upon  the  connections  in  which  the  elementary  parts  stand  with 
each  other,  there  can  be  no  doubt. 

Moreover,  the  elementary  parts  of  the  nervous  system,  inasmuch 
as  they  have  the  general  adaptation  necessary  to  the  performance 
of  nervous  functions,  can  "  learn  "  (so  to  speak)  to  perform  the 
more  specific  of  these  functions — but  only  in  case  they  stand  in 
appropriate  connections.  The  repeated  action  of  the  nervous  ele- 
ments in  specific  functions  fits  them  the  better  to  act  in  the  same 
functions.  The  effect  of  the  exercise  of  any  function  in  the  past 
may  be  "  stored  uj)  "  so  as  to  increase  the  facility  of  the  nervous 
structure  to  exercise  again  every  similar  function.  Thus,  different 
elementary  parts  of  the  nervous  system,  if  at  first  forced  by  circum- 
stances to  become  active  in  a  given  way,  may  by  repeating  the 
activity  gain  a  position  of  facility  and  value  like  that  belonging  to 
other  parts  whose  so-called  normal  action  lies  in  this  particular 
way.  This  law  of  habit  in  the  nervous  system  explains  much  of 
the  behavior  of  the  nerve-muscle  machine,  or  of  the  decapitated 
frog,  etc.,  under  artificial  stimuli ;  it  also  underlies  the  theory  of  the 
sensory-motor  effects  attributed  to  centres  in  the  spinal  cord  and 
basal  ganglia  ;  it  throws  light  upon  the  physical  basis  of  our  ex- 
perience in  learning  to  walk,  talk,  play  upon  musical  instruments, 
or  handle  tools,  as  well  as  upon  the  transmission  from  generation 
to  generation  of  minute  bodily  characteristics.  Both  the  law  of 
specific  energy  and  the  law  of  habit  undoubtedly  apj^ly  to  the  func- 
tions of  the  cerebral  cortex. 

The  remaining  two  of  the  three  principles  alluded  to  above  may 
be  said  to  follow  from  the  first  ;  they  are  the  princij)le  of  localized 
function  and  the  principle  of  siibstitulion.  The  former  asserts 
that,  in  the  normal  condition  of  the  nervous  system,  all  jjarts  have 
not  the  same  definite  functions.  Inasmuch  as  the  functions  of  the 
different   elementary  parts  necessarily  depend   upon  the   manner 


NATURE   OF   THE   CEREBRAL   "  FIELDS."  301 

in  whicli  tliey  are  combined  and  connected,  the  composite  parts 
or  organs  thus  formed  must  also  have  certain  normal  functions. 
But  such  composite  parts  or  organs  have,  of  course,  a  definite  local- 
ity ;  hence  the  functions  of  the  nervous  mechanism  must  be  more 
or  less  definitely  localized.  Nor  can  the  principle  be  suspected 
of  a  disposition  to  stop  short  off  and  abdicate  its  authority,  when 
we  reach  the  region  of  the  cerebral  cortex.  There  is  nothing  in 
the  structure  of  the  cortex  to  show  why  the  general  law  of  differen- 
tiation of  function  should  be  inapplicable  there.  On  the  contrary, 
everything  in  both  its  anatomy  and  physiology  indicates  that  the 
principle  of  localized  function  does  apply,  in  some  sort,  to  the  cere- 
bral hemispheres. 

So-called  "centres,"  or  "areas,"  or  "fields,"  of  the  cerebrum  are 
in  no  case,  however,  to  be  regarded  as  portions  of  its  nervous  sub- 
stance that  can  be  marked  oft'  by  fixed  lines  for  the  confinement 
of  definite  functions  within  rigid  limits.  These  areas  are  some- 
what different  for  different  brains  of  the  same  species  ;  the}'  widen 
when  a  heightened  energy  is  demanded  of  them ;  their  centres 
are  neither  mathematical  points  nor  very  minute  collections  of 
cells.  They  are  not  composed  of  elements  which  have,  each  one, 
a  fixed  and  unchangeable  value,  and  a  definite  function,  as  though 
the  number  of  mental  operations  assigned  to  a  locality  needed  to 
be  jDrecisely  matched  by  the  separate  nerve-fibi'es  and  nerve-cells  of 
the  locality.  Nor  are  these  areas  perfectly  isolated  localities  ;  on 
the  contrary,  they  obviously  overlap  each  other  in  certain  cases. 
According  to  the  true  statement  of  Luciani,  "the  single  centres 
in  the  sensory-motor  zone  are  so  completely  bound  up  with,  and, 
so  to  speak,  let  into  one  another,  that  it  is  not  possible  to  divide 
them  with  a  clear  and  definite  line,  such  as  is  the  case  when  the 
cortex  is  incised  and  removed  ;  so  that  in  destroying  a  centre  one 
necessarily  eliminates  a  portion  of  the  neighboring  centres."  Nev- 
ertheless, there  is  no  doubt  that  the  cerebral  functions  connected 
with  the  different  sensations  and  motions  of  the  peripheral  parts  of 
the  body  are  not  all  alike  exercised  by  all  parts  of  the  cerebrum. 
They  are  assigned  specifically  to  those  regions  which  alone  have  the 
proper  structure  and  stand  in  the  proper  relations. 

Furthermore,  the  functions  of  the  cerebrum  are  not  absolutely 
confined  to  those  centres  with  which,  under  ordinary  circumstances, 
they  are  chiefly  or  wholly  connected  ;  in  which,  that  is  to  say,  they 
are  localized.  If  such  centres,  for  any  reason,  become  incapacitated 
or  relatively  unfitted  to  perform  their  normal  functions,  the  same 
functions  may  be  performed  by  other  areas  of  the  cerebral  cortex, 
provided  these  areas  also  stand  in  the  proper  connections.     This 


302  SUMMARY    OF   RESULTS. 

is  the  principle  of  substitution.  It  is  clue  to  its  working  that 
animals  subjected  to  exj)eriments  in  extirpation,  as  a  rule,  so 
largely  recover  the  powers  of  sensation  or  motion  which  they  have 
temporarily  lost.  It  is  on  this  class  of  phenomena  that  Goltz  rests 
much  of  his  argument.  In  the  cerebral  hemispheres,  however,  the 
principle  of  substitution  does  not  overstep  all  limits,  nor  does  it 
operate  arbitrarily.  The  portions  of  the  same  hemisphere  that 
are  just  adjacent  to  the  so-called  centres — the  larger  areas  sur- 
rounding or  contiguous  to  the  smallei' — and,  on  account  of  its  bi- 
lateral structure,  the  corresponding  portions  of  the  other  hemi- 
sphere, are  in  general  those  best  capable  of  exercising  such  substi- 
tutive functions.  It  may  be  doubted  whether  these  portions  do 
not,  in  all  ordinary  cases,  cover  the  entire  limits  within  which  the 
principle  of  substitution  can  act.  Such  substitutive  functions  im- 
prove under  the  law  of  habit  to  which  the  organs  of  the  cerebral 
cortex  are  subjected. 

The  connections  between  the  different  cerebral  areas  and  their 
functions  are  so  complex  and  subtile  that  physiological  science  wiU 
need  a  long  time  to  disentangle  them  ;  it  may  be  doubted  whether 
it  will  ever  succeed  in  doing  this  completely.  The  connections 
among  the  phenomena  of  conscious  sensation,  volition,  ideation, 
and  thought  are  at  least  equally  subtile  and  complex.  Will  psy- 
chology ever  disentangle  these  connections  ? 

The  bearing  of  the  subject  on  our  conclusions  concerning  the 
nature  of  the  mind  and  its  connection  with  the  body  will  be  con- 
sidered elsewhere. 


CHAPTER  III. 
THE  QUALITY  OF  SENSATIONS. 

§  1.  The  world  of  ordinary  experience  consists  of  a  great  number 
of  so-called  '•'  things  "  that  are  known  to  us  by  their  distinguishing 
qualities.  Although  each  one  of  these  things  is  believed  to  be  a 
separate  existence,  they  are  all  perceived  as  having  certain  common 
characteristics,  and  as  standing  in  certain  relations  to  each  other, 
of  space,  time,  and  action.  It  is  with  the  things,  their  common 
qualities  and  mutual  relations,  that  unreflecting  practical  life  is 
chiefly  concerned.  But  even  without  special  reflection,  everyone 
learns  that  his  knowledge  of  such  external  objects  dejDends  upon 
the  kind  and  degree  of  the  effect  they  exercise  upon  his  conscious- 
ness through  the  senses.  Attention  is  thus  turned  from  the  things 
themselves  to  the  sensations  produced  in  us  by  their  action.  The 
variety  of  such  sensations,  at  first  bewilderingly  great,  is  soon  re- 
duced to  some  order  by  a  classification  referring  them  to  the  dif- 
ferent organs  through  which  they  come.  Thus,  certain  sensations 
are  received  through  the  nose,  others  through  the  mouth,  the  ear, 
the  eye,  or  the  skin — especially  as  covering  that  part  of  the  body 
(the  hand)  which  is  most  active  in  touch.  Smell,  taste,  hearing, 
sight,  and  touch  are  the  five  classes  of  sensation,  as  the  grouping 
is  made  by  the  unprejudiced  judgment  of  all. 

A  further  rough  and  scientifically  inadequate  classification  takes 
place  among  the  sensations  of  the  same  sense.  Those  of  smell,  in- 
deed, defy  classification,  whether  popular  or  scientific.  Among 
tastes,  the  most  familiar  are  easily  distinguished  ;  such  are  the 
sweet,  the  sour,  and  the  bitter.  The  two  principal  classes  of  sensa- 
tions of  sound  are  easily  discriminated,  as  either  noises  or  musical 
tones  ;  the  former  are  further  classified  as  respects  the  character  of 
the  feeling  which  accompanies  them,  and  the  latter  as  high  or  low 
in  pitch.  The  different  more  prominent  colors — including  black 
and  Avhite— are  recognized  by  all  persons  of  normal  vision  as 
modes  of  the  sensations  of  sight ;  hence  the  colors  commonly 
named,  and  the  various  so-called  "shades"  of  these  colors.  That 
more  than  one  class  of  sensations  arise  through  the  skin  is  shown 


304  THE  KINDS    OF   SENSATIOIST. 

by  the  popular  use  of  the  word  to  "feel."  Things /eeZ  hard  and 
soft,  smooth  and  rough,  as  weU  as  warm  and  cold.  But  things  are 
also  said  to  feel  heavy  or  light.  The  feeling  by  which  their  weight 
is  estimated,  however,  is  only  ascribed  in  a  very  indefinite  way  to 
the  parts  of  the  body  that  are  chiefly  concerned  in  passively  sup- 
porting, or  actively  lifting,  or  pushing  against  their  weight.  The 
particular  use  of  tactual  feeling,  as  well  as  the  general  use  of  the 
muscular  sense,  in  gaining  this  class  of  sensations  is  little  noticed 
by  ordinary  reflection. 

§  2.  All  the  sensations  are  also  regarded  as  having  some  place 
in  a  scale  of  degrees  of  sensation  ;  they  are  either  strong  or  faint, 
or  else  He  somewhere  between  the  two  extremes.  They  are  also 
habitually  thought  of  as  related  in  time,  and  as  being  connected 
with  the  motion  in  space  of  the  objects  that  occasion  them.  Of 
the  molecular  action  of  their  stimuli  upon  the  end-organs  of  special 
sense  ;  of  the  hidden  chemical,  electrical,  or  other  processes  con- 
nected with  the  activity  of  the  peripheral  and  central  nervous  sys- 
tem ;  of  the  physiological,  psycho-physical,  and  psychological  laws 
under  which  the  mind  reacts  in  the  form  of  simple  sensations,  and 
combines  these  sensations  into  the  composite  objects  of  sense  ;  of 
all  these  and  other  similar  matters,  the  unreflecting  conception  of 
sensation  takes  no  account. 

§  3.  It  is  obvious  that  the  analysis  of  sense-percepts  which  suf- 
fices for  working-day  life  will  in  no  respect  answer  the  demands  of 
science.  Its  "  common-sense  "  character  is  a  distinct  mark  of  its 
inadequacy.  An  adequate  scientific  treatment  of  this  branch  of 
Physiological  Psychology  requires  at  least  four  things  :  (1)  to  dis- 
tinguish the  simple  sensations  from  those  complex  objects  of  experi- 
ence with  which  alone  our  adult  consciousness  is  familiar  ;  (2)  to 
point  out  the  varieties  of  quality  and  degrees  of  quantity  which  be- 
long to  these  sensations,  and  to  discover  the  laws  which  relate  them 
to  changes  in  the  form  and  intensity  of  their  stimuli ;  (3)  to  show 
how  the  simple  sensations  are  constructed  by  the  mind  into  the  so- 
called  "presentations  of  sense"  under  mental  laws  of  time-form 
and  space-form  ;  and  (4)  to  indicate  how  far,  if  at  all,  the  higher 
mental  activities  of  association,  memory,  will,  and  judgment,  may 
be  brought  under  laws  similar  to  those  upon  which  the  formation 
of  these  presentations  of  sense  depends.  It  is  upon  these  four 
heads  of  inquiry  that  modern  psychology,  as  studied  from  the 
psycho-physical  point  of  view,  has  expended  most  of  its  painstak- 
ing researches.  Its  success  has  been  by  no  means  complete.  All 
these  fields  of  inquiry  still  include  many  unanswered  questions  ;  all 
of  them  present  the  results  of  researches  that  seem  in  various  re- 


THE   ANALYSIS    OF   SENSATIONS.  305 

spects  conflicting.  Yet  it  is  precisely  in  these  fields  that  modern 
psychology  has  achieved  its  most  brilliant  successes.  It  has  thrown 
a  flood  of  new  light  upon  the  essential  nature  and  growth  of  hu- 
man experience.  It  has  profoundly  influenced  the  current  views 
on  metaphysics.  It  has  contributed  important  factors  toward  tlie 
solution  of  certain  questions  of  interest  to  ethics  and  religion.  It 
has  given  us  a  new  jDoint  of  view  for  I'enewiug  the  ancient  debate 
between  Materialism  and  Spiritualism. 

§  4.  The  distinctions  with  which  scientific  analysis  begins  are  to 
a  large  extent  received  from  ordinary  experience.  Some  of  the 
most  essential  of  the  distinctions  are  confirmed  by  the  results  of 
this  analysis.  They  all,  however,  require  to  be  carried  farther  and 
to  be  fixed  with  much  more  of  accuracy  than  belongs  to  the  im- 
pressions of  common  life.  New  distinctions  also  have  to  be  intro- 
duced. For  example,  scientific  investigation  maintains  the  differ- 
ence between  sensations  of  smell  and  sensations  of  taste ;  but  it 
points  out  what  is  not  ordinarily  apparent — namely,  that  certain 
results  commonly  referred  to  the  latter  sense  really  belong  to  the 
former.  It  also  adds  the  sensations  of  the  muscular  sense  to  the 
classes  popularly  described ;  and  it  discriminates  more  clearly  be- 
tween two  distinct  kinds  of  sensation  that  have  the  skin  for  their 
organ — namely,  temperature  and  pressure. 

Psycho-physical  science,  moreover,  accepts  the  common  distinc- 
tion between  the  quality  and  the  quantity  of  the  different  sensa- 
tions. But  it  describes  with  all  possible  accuracy  the  limits  Avithin 
which  alone  this  distinction  can  be  carried  out.  It  shows  that  the 
quality  and  quantity  of  sensation  are  inseparably  connected ;  that, 
as  Lotze  held  (a  view  confirmed  by  von  Kries  and  others),  changes 
in  quality  can  be  distinguished  from  changes  in  intensity,  with 
perfect  confidence,  only  in  the  case  of  sensations  of  hearing.  It  is 
possible  that  even  here  the  distinction  is  largely  made  on  the  basis 
of  complex  experience.  Very  intense  sensations  of  heat  and  cold  so 
far  change  their  specific  character  as  to  tend  to  pass  into  each  other, 
or,  perhaps,  to  become  submerged  in  a  common  tone  of  painful 
feeling.  Minimum  sensations  of  heat  and  pressure  are  difficult  to 
distinguish  from  each  other ;  maximum  sensations  of  pressure  are 
likely  to  lose  the  characteristic  quality  of  touch  and  be  displaced 
by  sensations  of  pain.  To  treat  scientifically  of  the  quality  of 
sensations  requires,  then,  a  large  amount  of  the  most  careful 
analysis. 

§  5.  It  is  essential,  in  the  first  place,  to  distinguish  "  simple 
sensations"  from  "  presentations  of  sense,"  or  those  complex  ob- 
jects of  consciousness  which  result  from  an  act  of  mental  synthesis 
20 


306  THE   KINDS   OF   SENSATION. 

on  the  basis  of  several  simultaneous  affections  of  sense.  As  respects 
developed  experience,  the  simple  sensation  is  a  necessary  fiction  of 
psycho-physical  science.  Consciousness  is  scarcely  more  able  di- 
rectly to  analyze  a  presentation  of  sense  into  those  factors  out  of 
which  it  originated  than  it  is  to  analyze  a  drop  of  water  into  its 
component  oxygen  and  hydrogen  gases.  Simple  sensations,  there- 
fore, are  not  objects  which  can  be  examined  in  the  direct  light  of 
introspection.  Yet  they  are  factors  which,  as  scientific  analysis 
shows,  actually  enter  into  all  such  objects  as  can  properly  be  sjDoken 
of  under  the  term  "presentations  of  sense."  Any  sensation  which 
is  absolutely  unanalyzable  with  respect  to  distinctions  of  quality', 
and  which,  therefore,  cannot  be  considered  as  consisting  of  com- 
ponent parts,  is  called  simple.  It  is  distinguished  as  a  sensation 
from  all  other  elementary  forms  of  feeling  or  knowledge,  by  the 
relation  which  it  sustains  to  the  jDresentations  of  sense.  A  sensa- 
tion, unlike  the  feeling  of  grief,  of  desire,  or  of  weariness,  etc.,  is  a 
potential  factor  of  a  material  object.  Through  the  senses  we  know 
"things;"  not,  indeed,  as  though  they  apj^eared  before  the  mind 
by  immediate  apprehension  in  the  form  of  exact  copies  of  extra- 
mental  realities.  But  every  sensation  is  an  affection  of  the  mind 
recognized  as  connected  with  an  extra-mental  reality,  through  the 
activity  of  the  senses.  Simple  sensations  are  those  elementary 
factors,  themselves  indecomposable,  out  of  which  the  presentations 
of  sense  are  composed.  The  objects  of  sense,  however,  do  not  have 
the  character  of  mere  compounds  of  simjDle  sensations.  Sensations 
must  not  only  be  associated  and  compounded,  but  also  localized 
and  projected  without  (that  is,  set  in  systematic  relations  of  sj)ace- 
form),  in  order  to  constitute  the  objects  of  sense. 

§  6.  The  foregoing  remai'ks  suffice  to  indicate,  in  a  preliminary 
way,  what  is  the  nature  and  value  of  the  psycho-phj'sical  investi- 
gation of  sensation.  We  inquire,  in  the  next  two  chapters,  as  to 
the  Quality  of  Sensations.  The  inquiry,  when  conducted  from  the 
psycho-physical  point  of  view,  involves  an  answer  to  three  questions  : 
(1)  What  is  the  precise  locality  in  the  organism  where  the  specific 
excitation  which  occasions  each  kind  of  sensation  originates  ;  and 
what  is  the  natui-e  of  the  action  of  the  stimulus  in  producing  such 
excitation?  (2)  What  are  the  kinds  of  sensations  which  appear  in 
consciousness  as  the  result  of  the  various  excitations?  (3)  What  are 
the  laws  by  which  the  quality  of  the  sensations  is  related  to  the 
kinds  of  excitation?  Neither  of  these  three  questions  can  be 
answered  completel}'.  The  investigation  of  the  first  is  much  re- 
stricted by  our  almost  complete  ignorance  of  those  processes  in 
the    central  organs  that  are  in  all   cases  the  proximate  internal 


SPECIFIC    ENEKGY    OF   JSTERVES.  307 

stimuli  or  immediate  antecedents  of  the  sensations.  Moreover,  our 
knowledge  of  the  intimate  structure  of  the  end-organs  of  sense, 
and  of  the  nature  of  the  physical  processes  which  excite  them,  is 
still  very  incomplete.  The  detection  of  obscure  but  important  dif- 
ferences in  the  qualities  of  conscious  states  of  sensation  is  by  no 
means  easy  ;  it  requires  great  skill,  strict  and  trained  attention, 
and  unwearied  rej)etition  of  experiment.  But  these  conditions  of 
success  have  a  great  effect  in  altering  the  quality  of  the  sensations 
themselves.  Besides  all  this,  remarkable  idiosyncrasies  not  infre- 
quently appear ;  and  language  can  only  imperfectly  describe  even 
the  most  common  factors  of  the  varied  and  living  experiences  wdth 
which  science  tries  to  deal. 

In  investigating  the  laws  that  define  the  relations  between  our 
subjective  experience,  called  sensation,  and  objective  phenomena 
in  the  shape  of  physical  energy  acting  uj^on  the  nervous  mechanism, 
there  is  often  the  greatest  doubt  as  to  what  manner  of  laws  are  be- 
ing investigated.  They  may  be  considered  as  purely  physiological, 
or  as  psycho-physical,  or  as  purely  psychological.  It  is  not  strange, 
therefore,  that  different  theories  exist  for  accounting  for  all  the 
more  important  groups  of  facts,  deijending  uj^on  the  emphasis  laid 
by  different  investigators  upon  the  value  of  each  of  the  three  possi- 
ble modes  of  explanation.  The  truth  is,  that  each  sensation  is  sepa- 
rated by  a  series  of  intricate  j)hysiological  and  psychical  processes 
from  the  application  of  the  stimulus  in  the  gross,  as  it  were,  to  the 
end-organ  of  sense. 

§  7.  The  authority  of  one  great  law  is  involved,  as  a  silent 
assumption,  in  all  discussion  of  the  quality  of  sensations.  This  law 
is  known  as  the  law  of  the  Specific  Energy  of  the  Nerves.  It  has 
already  been  shown  (Part  I.,  chap.  I.,  §  35)  that  any  such  dis- 
tinction of  the  kinds  of  nerve-fibres  as  denies  their  possession  of 
common  functions  cannot  be  maintained.  But  the  phenomena 
of  sensation  cannot  be  explained  without  a  much  more  extended 
application  of  this  law  than  has  thus  far  been  found  necessary. 
Distinctions  of  quality  in  sensation  depend  upon  the  excitation  of 
specific  corresponding  elements  of  the  nervous  system.  That  only 
the  optic  nerve  is  capable,  when  excited,  of  exercising  the  physio- 
logical function  upon  which  sensations  of  light  and  color  depend, 
does  not  admit  of  doubt ;  the  same  specific  quality  cannot  be 
denied  to  the  functional  activity  of  the  nerves  of  smell,  taste,  hear- 
ing, and  touch.  Moreover,  in  the  end-organs  of  each  of  these 
senses,  provision  must  be  made  for  a  further  differentiation  of 
function.  What  is  the  nature  of  the  evidence,  and  what  conclu- 
sions must  be  drawn  from  it,  will  be  best  appreciated  at  a  later  pe- 


308  SENSATIONS    OF   SMELL   AND   TASTE. 

riod  in  the  discussion.  Meantime  we  find  ourselves  obliged  to  as- 
sume the  existence  of  some  law  of  the  specific  euex-gy  of  the  nervea 
of  special  sense. 

§  8.  Little  of  a  scientific  character  is  known  concerning  Sensa- 
tiona  of  Smell,  considered  as  respects  their  qualit}'.  Anatomy, 
chemistry,  and  physics  fail  to  furnish  definite  information  on  this 
point ;  experimental  physiology  as  aj)plied  to  the  lower  animals  is, 
of  course,  unsatisfactory  ;  and  the  appeal  to  human  consciousness 
asks  for  an  anatysis  of  which  it  is  incapable.  It  has  already  been 
shown  (Part  I.,  Chap.  V.)  that  the  part  of  the  mucous  membrane 
of  the  nasal  passages  known  as  regio  olfactoria  contains  the  end- 
organs  of  smell ;  the  specific  stimulus  of  the  organs  in  this  region 
is  applied  as  borne  thither  by  the  current  of  air,  and  almost,  if  not 
quite,  exclusively  in  the  act  of  inspiration.  In  order  that  any  sub- 
stance may  act  through  the  end- organs  on  the  nerve  (olfaclorius) 
which  is  spread  out  in  this  region,  it  must  either  exist  in  gaseous 
form  or  else  be  vaporizable  under  given  conditions  of  temperature. 
The  degree  of  temperature  at  which  different  substances  become 
odorous  therefore  varies  according  to  their  i^hysical  characteristics. 
For  example,  arsenic,  which  at  ordinary  temperatures  is  inodorous, 
when  raised  to  a  dark-red  heat  is  vaporized  and  the  vapor  excites 
an  intense  sensation  of  smell.  Fluid  bodies  which  give  off  an 
odorous  i-eek,  when  brought  in  fluid  form  into  contact  with  the 
mucous  membrane  of  the  regio  olfactoria  have  no  smell ;  if  this 
membrane  is  soaked  in  fluid  of  any  kind  whatever,  it  loses  for  a 
time  the  capacity  to  be  excited  witli  olfactory  impressions.  E.  H. 
Weber  '  discovered  that  if  the  head  be  placed  with  the  nostrils 
pointing  upward,  and  the  nasal  jDassages  be  then  filled  with  pure 
water,  sweetened  water,  or  a  mixture  of  water  and  eau  de  Cologne, 
after  these  passages  are  emptied  the  sense  of  smell  is,  in  all  cases, 
temporarily  lost ;  even  when  Cologne  is  used,  with  the  exception 
of  the  instant  at  which  the  fluid  is  poured  in,  no  odor  can  be  per- 
ceived. Subsequent  observers  have  confirmed  the  experiments  of 
Weber.  One  investigator  ^  lost  all  sense  of  smell,  even  for  acetic 
acid  and  ammonia,  for  a  period  of  half  a  minute  ;  another  for  five 
minutes,  and  the  sense  in  its  full  acuteness  did  not  return  for  nearly 
half  an  hour.  Whether  this  effect  of  the  fluid  is  due  to  impair- 
ment of  the  end-apparatus  of  smell  by  soaking  it  (so  Valentin),  or 
to  the  mechanical  barrier  which  the  layer  of  foreign  substances 
interposes  between  the  odorous  particles  and  this  apparatus  (so 
FrohHch),  we  cannot  say  ;  it  may  be  due  to  both  causes.     Contrary 

1  See  Archiv  f.  Anat  ,  Physiol.,  etc..  1847,  p.  257. 
sprolilicli,  in  Sitzgsber.  d.  Wiener  Acad.,  1851,  VI.,  p.  322. 


THE   STIMULUS   OF   SMELL.  309 

to  the  assertion  of  Wundt,'  that  probably  no  gases  or  vapors,  except 
atmospheric  air  and  its  constituents,  are  absolutely  inodorous,  so 
far  as  we  have  present  information  a  number  of  gaseous  and  va- 
porizable  substances  are  so  ;  and  no  reason  is  known  for  such 
apparent  exceptions  to  the  rule. 

§  9.  The  stimulus  of  smell  is  supposed  to  consist  in  certain  ex- 
ceedingly minute  particles  contained  in  the  odorous  gas  or  vapor 
which  is  drawn  in  with  the  current  of  air  over  the  mucous  mem- 
brane of  the  regio  olfactoria.  The  question  is  as  yet  scarcely  de- 
cided, whether  other  forms  of  stimulus,  besides  these  odorous 
particles — mechanical,  electrical,  thermic,  or  so-called  subjective — 
can  excite  the  sensation  of  smell.  Tlie  older  experimenters  (Volta, 
Pfaff,  Fowler,  and  Humboldt)  failed  to  obtain  any  certain  proof 
that  the  electrical  current  is  an  excitant  of  this  sense.  In  one  place, 
however,  Pfaff  speaks  of  a  sensation  resembling  the  smell  of  sul- 
phur as  caused  by  the  apj)lication  of  electricity  to  the  sensory  pas- 
sages of  the  nose.  Ritter  (in  1798)  experimented  by  using  bits  of 
graphite  and  zinc  thrust  into  these  passages,  and  also  by  holding 
one  pole  of  a  battery  in  the  hand  and  placing  the  other  in  the  nos- 
tril. In  the  latter  way  he  thought  that  he  excited  a  genuine  sj)e- 
cific  sensation  of  this  sense.  He  describes  the  positive  pole  in  the 
nostril  as  producing  an  inclination  to  sneeze  and  a  trace  of  a  smell 
like  that  of  "ammonia  ; "  the  negative  pole  placed  there  does  away 
with  this  inclination  and  produces  a  kind  of  "  sour  "  smell.  Such 
phenomena  are  probably,  however,  all  to  be  assigned  to  the  nerves 
of  taste,  touch,  and  common  feeling.  More  recent  investigations 
have  done  little  to  remove  the  reasons  for  doubt."  The  smell  of 
phosphorus  which  is  developed  by  the  action  of  the  electrical  ma- 
chine is  probably  due  to  the  ozone  set  free  ;  it  is  not  a  case,  then, 
of  the  direct  excitation  by  electricity  of  the  sensation  of  smell. 
Some  physiologists  (notably  Valentin)  have  observed  that  this  sen- 
sation may  be  awakened  by  mechanical  stimulation,  such  as  strong 
vibi'ation  of  the  nostrils,  violent  sneezing,  etc. ;  others  have  failed 
to  produce  this  specific  sensory  effect  in  such  ways.  It  does  not 
appear  that  thermic  stimulation  will  excite  the  sensation  of  smeU. 

Experiments  to  prove  that  subjective  sensations  of  smell  may  be 
produced  b}' injecting  odorous  substances  into  the  veins  of  animals 
are  very  uncertain.  Human  pathological  cases,  in  spite  of  the  cus- 
tomary indefiniteness  of  the  patient's  testimony  as  to  the  nature  of 
his  sensory  affection,  show  that  compression  of  the  olfactory  nerve 

'  Gruiidziige  d.  physiolog.  Psycliologie,  i. ,  384;  comp  von  Vintschgau,  in 
Hermann's  Kandb    d.  Physiol.,  HI.,  ii.,  p   261  f. 

^See  Roaeutiial,  iu  Archiv  f.  Auat.,  Physiol.,  etc.,  1860,  pp.  217  ff. 


310  SENSATIONS   or   SMELL   AND   TASTE. 

by  tumors,  etc.,  may  produce  sensations  of  smell.  Disturbances  of 
the  central  organs,  such  as  occur  in  certain  cases  of  insanity,  may 
doubtless  have  the  same  result.  The  powerful  effect  which  some 
odors  have  upon  the  brains  of  certain  persons,  so  that  nausea,  gid- 
diness, and  other  disturbances  of  feeling  result,  scarcely  needs 
mention  ;  it  cannot  all  be  resolved  into  mental  associations  con- 
nected with  the  sense-impressions. 

§  10.  No  approach  can  be  made  toward  a  scientific  classification 
of  the  kinds  of  smells.'  This  specific  sensation  must,  however,  be 
carefully  distinguished  from  the  other  forms  of  feeling  with  which 
it  is  most  closely  allied.  Many  supposed  sensations  of  taste  are 
really  sensations  of  smell.  Substances  like  ammonia  and  acetic 
acid  powerfully  excite  the  sensations  of  touch  and  common  feeling 
through  their  action  on  the  trigeminus  as  well  as  the  olfactory 
nerve.  Other  sensations  of  touch  and  of  the  muscular  sense  are 
reflesly  occasioned  in  such  cases,  and  blend  with  the  specific  sensa- 
tions of  smell  in  the  total  mental  result.  But  of  all  the  attempts  to 
classify  the  qualitatively  jDure  sensations  of  this  sense,  none  can  be 
said  to  have  any  scientific  value.  The  division  into  pleasant  and 
unpleasant  smells  depends  upon  the  idiosyncrasies  of  individuals  ; 
to  some  the  smell  of  burning  feathers,  of  assafoetida,  of  valerian,  or 
of  rank  cheese,  is  pleasant.  Frohlich's  "  classification  into  those 
which  excite  merely  the  olfactory  nerve,  and  those  which  call  out 
other  sensations  reflexfy  through  their  action  on  the  trigeminus,  is 
purely  physiological  and  not  psycho-physical ;  moreover,  it  does 
not  apply  to  sensations  of  smell,  as  such.  When  we  classify  the  sen- 
sations according  to  the  objects  which  produce  them — as  j)ractieally 
we  are  obliged  to  do — we  are  not  distinguishing  the  qualities  of 
our  feeling  ;  the  smell  of  a  rose  does  not  belong  to  a  class  of  sen- 
sations as  does  a  sour  taste  or  the  color  red.  No  known  principle 
will  bring  order  out  of  the  bewildering  complexity  of  this  sense. 

Sensations  of  smell  cannot,  like  those  of  pressure,  hearing,  and 
sight,  be  schematized  or  represented  as  standing  in  any  definite 
local  or  mathematical  relations  to  each  other.  Smells  cannot  be  con- 
ceived of  as  having  a  scale  of  pitch,  or  triangle  of  color-tones.  As 
Wundt '  declares,  the  sensations  of  smell  form  "  a  discrete  mani- 
foldness  Avhich  has  an  unknown  arrangement." 

§  11.  The  properties  which  any  substance  must  j)ossess  in  order 
to  be  odorous,  and  the  nature  of  the  action  of  the  odorous  particles 

'  For  the  entire  subject,  see  von  Vintschgau,  in  Hermann's  Handb.  4 
Physiol.,  IIL,  il,  p.  2G6  f. 

•^Sitzgsber.  d.  Wiener  Acad.,  1851,  VI.,  p.  322  f. 
^Physiolog.  Psychologie,  i  ,  p.  386. 


NATUEE  OF  ODOROUS  SUBSTANCES.        311 

upon  the  end-organ  of  smell,  are  wholly  unknown — as  much  so 
now  as  when,  more  than  a  half-century  since,  Cloquet  confessed  the 
complete  ignorance  of  the  scientific  world  on  these  matters.  A 
great  variety''  of  phenomena  appear,  but  no  known  laAV  has  control 
of  them.  Some  plants  are  odorous  by  day  alone,  others  by  night 
alone  ;  still  others  only  in  the  morning.  Some  plants  have  a  smell 
when  dried  ;  others  give  off  only  a  weak  odor  when  dry,  but  a 
stronger  one  when  moistened.  Of  course,  the  effect  of  any  odorous 
substance  depends  upon  the  ease  wdth  which  it  may  be  vaporized, 
and  the  speed  and  extent  of  its  diffusion  through  the  atmosphere. 
Camphor,  musk,  and  other  similar  substances  are  distinguished  for 
their  long-continued  and  far-reaching  effects. 

The  discovery  of  Eomieu,  in  1756,  that  small  bits  of  camphor  on 
the  surface  of  water  have  a  rotary  motion,  has  called  out  various 
investigations  in  the  line  suggested  by  this  fact.  Provost  subse- 
quently (1799)  observed  that  other  odorous  bodies  have  a  similar 
motion  on  the  surface  of  water,  and  that  a  very  thin  layer  of  water 
on  a  perfectly  clear  plate  or  glass  withdraws  itself  as  soon  as  jduI- 
verized  camphor  is  laid  upon  it.  More  recently  still,  Liegeois  has 
noticed  the  same  phenomena,  wholly  or  in  part,  exhibited  by  some 
two  hundred  odorous  substances  of  either  vegetable  or  animal  struct- 
ure. Minerals,  according  to  this  observer,  do  not  behave  in  the 
same  way.  Some  of  these  odorous  substances  seem  to  inhibit  or 
check  the  rotar}^  motion  in  others.  He  concludes  that  we  are  jus- 
tified in  believing  odorous  substances  to  have  the  power,  especially 
when  in  contact  with  water,  of  setting  up  a  motion  of  these  outside 
particles  which  distributes  them  through  the  atmosphere  so  that 
they  reach  the  mucous  membrane  of  the  nasal  passages.  Just  how 
they  act  upon  the  end-apparatus  there  it  is  impossible  to  say.  The 
researches  of  Tyndall  '  and  others  as  to  the  influence  which  odorous 
particles  of  different  substances  have  upon  the  capacity  of  the  air 
to  absorb  heat  may  possibly  be  combined  with  the  foregoing  re- 
searches in  a  way  to  suggest  some  tenable  hj-pothesis  touching  the 
nature  and  action  of  the  stimuli  of  this  sense  ;  but  thus  far,  as  has 
been  said,  we  cannot  go  beyond  a  confession  of  ignorance. 

§  12.  The  condition  of  scientific  attainment  as  to  sensations  of 
taste  and  their  stimuli  is  only  little  better  than  that  as  to  the  allied 
sense  of  smell.  The  adeqnate  specific  stimulus  for  the  nerves  of 
this  sense  consists  in  certain  tastable  substances  ;  such  substances, 
however,  do  not  excite  the  end-apparatus  unless  they  act  upon  it 
under  definite  conditions.  Only  fluid  bodies,  or  such  as  are  at 
least  to  some  small  degree  soluble  in  a  fluid  or  menstruum,  excite 
'  Heat  as  a  Mode  of  Motion,  pp.  341  ff.     New  York,  1868. 


312  SENSATIONS    OF    SMELL   AND    TASTE. 

sensations  of  taste  ;  absolutely  insoluble  bodies  are,  without  excep- 
tion, tasteless.  This  fact  may  be  due  to  the  concealed  position  of  the 
inner  cells  of  the  gustatory  flasks,  which  is  such  that  they  cannot  be 
reached  by  substances  undissolved.  By  no  means  all  soluble  sub- 
stances have  a  taste.  No  known  law  regulates  the  relation  between 
the  solubility  of  bodies  and  their  power  to  excite  sensations  of  this 
class.  It  is  disputed  whether  any  of  the  gases  are  direct  excitants 
of  the  end-organs  of  taste.  The  monograph  of  A.  Stick  '  maintains 
the  tastable  character  of  certain  gases,  on  the  ground  that  a  stream 
of  them,  let  fall  upon  the  tongue  when  dry  (so  that  they  cannot  well 
be  absorbed  by  the  saliva),  produces  the  peculiar  sensations  of 
taste  which  these  gases  are  known  to  possess.  A  stream  of  car- 
bonic-acid gas,  for  example,  when  acting  on  the  dry  edge  of  the 
tongue,  has  a  taste  which  is  described  as  sweetish  sour.  It  is  diffi- 
cult, however,  to  secure  such  a  degree  of  dryness  of  the  tongue  as 
will  not  leave  a  moist  capillary  layer  ;  diflficult,  also,  to  exclude  all 
the  connected  sensations  of  smell  and  common  feeling.'' 

It  is  doubtful  whether  the  sensation  of  taste  can  be  excited  by 
mechanical  means  ;  and  there  is  no  j)roof  that  heat  can  irritate  the 
gustatory  nerves.  Certain  authorities  of  the  first  rank  have  indeed 
described  specific  sensations  of  taste  as  mingled  with  the  feelings 
which  follow  rubbing,  pricking,  and  pressing  the  tongue.  Henle 
observed  a  saltish  taste  to  be  excited  by  passing  a  current  of  air 
over  the  tongue  ;  Wagner  a  bitter  taste  by  pressing  down  the  base 
of  the  tongue  with  the  dry  finger  ;  Dr.  Baly  an  acid  or  a  saltish 
taste  by  repeatedly  and  lightly  tapj)ing  the  end  of  the  tongue. 

The  long-debated  question  as  to  the  electrical  stimulation  of  this 
sense  seems  now  to  be  decided  affiinnatively.^  It  was  discovered  in 
1752  that  the  application  of  two  different  metals  to  the  tongue  is 
followed  by  a  peculiar  sensation  of  taste.  Volta  recognized  the 
fact  that  the  effect  of  the  metals  is  due  to  the  electrical  current 
called  out  between  them.  If  the  cathode  is  laid  upon  the  upper 
surface  of  the  tip  of  the  tongue,  a  sensation  is  produced  by  the  cur- 
rent passing  out  which  is  variously  described  as  metallic,  acid  and 
metallic,  or  bitter  and  metallic,  etc. ;  but  if  the  anode  is  applied  to 
the  same  spot,  the  sensation  produced  by  the  entering  current  is 
described  as  acid,  or  acid  and  metallic,  or  bitter  and  metallic.  In 
the  former  case,  not  infrequently,  a  strong  cuxTent  is  needed  to  pro- 

'Ueber  d.  Schmeckbarkeit  d.  Gase,  Berlin,  1857;  article  in  Annalen  des 
Charite-Krankenhanses. 

■•*  See  von  Vintschgau,  in  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  19G  f. 

^  The  whole  question  is  discussed  by  von  Vintschgau,  ibid.,  p.  181  f.;  and 
Pfluger's  Archiv,  xx.,  pp.  81  ff. 


ELECTRICAL    STIMULUS    OF    TASTE.  313 

duce  any  sensation  at  all.  Since  the  discovery  of  electrolysis,  it 
has  been  objected  that  these  effects  are  due  to  the  decomposition 
of  the  fluids  of  the  mouth  and  the  consequent  accumulation  of  free 
acid  at  the  positive  and  free  alkali  at  the  negative  pole  ;  the}'  are 
therefore  not  to  be  ascribed  to  the  direct  action  of  the  electrical 
cui-rent  on  the  end-apparatus  of  sense.  Experiments  by  du  Bois- 
Eeymond,  Rosenthal, '  and  others  have  been  directed  toward  an- 
swering this  objection.  The  former  showed  that  when  a  chain  of 
four  persons  is  arranged  in  such  manner  as  to  send  a  current  of 
electricity  through  the  tongue  of  one,  the  eyeball  of  another,  and 
the  muscles  of  a  frog-preparation  held  by  two  of  the  four,  the  same 
current  will  cause  simultaneously  an  acid  taste,  a  flash  of  light,  and 
a  movement  of  the  animal's  muscles,  Rosenthal  discovered  that, 
if  two  persons  touch  the  tips  of  each  other's  tongues  while  one 
holds  in  a  moist  hand  the  positive  and  the  other  the  negative  pole, 
an  electric  current  Avill  cause  the  first  person  to  have  an  alkaline  and 
the  second  an  acid  taste.  Still  other  experiments  confirm  the 
opinion  that  sensations  of  this  sense  may  be  directlj'  due  to  elec- 
trical stimulation.  Attempts  have  been  made  to  prove  the  possi- 
bility of  exciting  subjective  sensations  of  taste  by  injecting  tasta- 
ble  substances  into  the  veins  of  animals  ;  but  the  psychology  of 
the  subject  has  reaped  no  results  from  these  attempts.  Most  of 
the  alleged  cases  of  such  subjective  origin  are  probably  due  to 
substances  really  brought  to  the  tongue  in  the  saliva.  It  is  worth 
remarking  here  that  sensations  of  taste  rarely  or  never  mingle  in 
our  dreams. 

§  13.  The  question  whether  atastable  substance  excites  precisely 
the  same  sensation  when  applied  to  all  portions  of  the  organs  of  taste 
is  a  difficult  one  to  answer  satisfactorily  (see  Part  I,  Chap.  V.,  § 
6).  The  tabulated  results  of  different  experimenters  upon  this 
question  disagree  considerably.  Such  disagreement  is  suggestive 
of  idiosyncrasies  of  taste,  and  of  doubt  whether  the  different  shades 
of  the  same  class  of  sensations  are  either  nicely  discriminated  or 
uniformly  described  by  most  persons.  Descriptions  which  speak 
of  the  sensations  aspi'ickly,  piquant,  cooling,  etc.,  show,  of  course,  a 
combination  of  sensations  of  common  feeling  with  those  of  special 
sense.  The  minor  varieties  of  taste  may  be  occasioned  in  a  manner 
similar  to  that  of  the  less  important  shades  of  color-sensations.  It 
seems  tolerably  well  established  that  sweet  and  sour  are  tasted 
chiefly  with  the  tip  of  the  tongue  ;  bitter  and  alkaline  with  its  roots. 
The  experiments  of  two  of  the  principal  observers,  Horn  and  Picht, 
agree  in  the  conclusion  that  nearly  all  substances  (even  sugar)  call 
'  Ueber  d.  elektrischen  Geschmack  ;  Archiv  f.  Anat.,  Physiol.,  1860,  p.  217 f. 


314  SENSATioisrs  or  smell  and  taste. 

out  a  bitterish  taste  when  applied  solely  to  the  papilloe  circum- 
vallatce. 

§  14.  Most  of  the  different  kinds  of  tastes  admit  of  being  con- 
sidered as  compounds  of  a  few  simple  sensations  of  this  sense  with 
each  other  and  with  sensations  of  smell,  touch,  common  feeling,  and 
muscular  sense.  Many  so-called  tastes  are  really  chiefly  smells. 
Physiologists  generally  distinguish  four  principal  classes  of  tastes — 
sweet,  bitter,  salt,  and  sour.  Wundt '  adds  to  these  four  the  alka- 
line and  the  metallic.  But  possibly  the  alkahne  may  be  considered  as 
a  modification  of  the  salt ;  and  the  metallic  is  probably  a  compound 
taste,  although  its  analysis  is  by  no  means  easy.  The  attempt  has 
been  made  by  Valentin  and  others  to  reduce  this  number  to  two — 
the  sweet  and  the  bitter.  The  sour  is  thus  considered  as  not  a  pure 
sensation  of  taste,  but  as  predominatingly  a  sensation  of  touch. 
Acids  in  concentrated  form  certainly  bring  into  action  the  nerves  of 
feehng  ;  but  in  very  dilute  form  they  seem  to  excite  purely  the  sensa- 
tion of  taste.  The  same  thing  is  true  of  saltish  substances.  The 
bitter  and  the  sweet  are  agreed  by  all  to  have  the  character  of  pure 
sensations  of  this  sjDecific  sense.  Powerful  reflex  sensations  of  the 
muscular  sense  are  occasioned  by  strong  stimulation  of  the  nerves 
of  the  tongue,  and  these  sensations  blend  with  the  specific  sensa- 
tions of  taste.  There  is  no  satisfactory  reason  to  be  given  for 
classing  the  sensation  of  nausea  under  the  sense  of  taste. 

The  primary  forms  of  taste  are  combined,  in  the  greatest  variety, 
with  an  indefinite  number  of  shades  under  each  of  them.  The 
hypothesis  of  four  or  more  specifically  different  forms  of  the  end- 
apparatus  corresponding  to  the  primary  forms  of  sensation — for 
example,  "bitter-tasting"  nerve-fibres,  "sweet-tasting"  nerve- 
fibres,  etc. — offers,  under  the  law  of  the  specific  energy  of  the 
nerves,  an  opportunity  for  explaining  all  the  phenomena  of  this 
sense  somewhat  similar  to  that  embraced  by  the  so-called  Young- 
Helmholtz  theory  of  color-sensations. 

§  15.  Concei'ning  that  in  tastable  substances  which  fits  them  to 
excite  the  end-apparatus  of  the  gustatory  nerves,  or  concerning  the 
molecular  action  of  such  substances,  we  have  no  information  what- 
ever. No  scale  of  stimuli,  considered  as  differing  in  the  rapidity  of 
their  vibration  and  corresponding  to  a  scale  of  resulting  sensations 
differing  in  pitch  or  tone,  can  be  made  out  for  sensations  of  taste. 
The  great  difficulties  which  accompany  experiments  uj)on  this 
sense,  and  the  fact  that  the  most  fundamental  questions  concerning 
its  activities  are  still  unanswered,  place  it  in  an  unsatisfactory  posi- 
tion only  less  hopeless  than  that  occupied  by  the  kindred  sense  of 
'  Playsiolog.  Psycliologie,  i.,  p.  382. 


SUBJECTIVE    CHARACTER   OF   SOUND.  315 

smell.  We  have  in  the  case  of  taste,  however,  the  very  great  ad- 
vantage of  being  able,  at  least  loosely,  to  classify  the  sensations 
Avhose  quality  we  are  considering. 

§  16.  On  passing  to  the  consideration  of  sensatiojis  of  sound  much 
more  help  is  received  from  the  science  of  physics.  But  modern  in- 
vestigations, in  the  form  in  which  they  concern  us,  do  not  go  back 
of  the  great  work  of  Helmholtz,'  who  made  the  entire  field  peculi- 
arly his  own.  Since  the  first  appearance  of  this  work,  the  subject 
has  also  been  greatly  enriched  by  the  original  researches  of  Oetting- 
en,^  Mach,'  Preyer,*  Hensen,'  Stumpf,"  and  others.  In  speaking 
of  the  stimuli  of  these  sensations,  we  are  still  comj)elled  to  refer 
chiefly  to  the  vibrations  of  air,  which  are  only  remote  excitants  of 
the  end-organs  of  this  sense.  Neither  physics  nor  physiology  has 
yet  been  able  to  fix  the  precise  locality  in  the  organism  (the  ner- 
vous structure  of  the  cochlea)  where  the  immediate  stimulation  of 
the  end-apparatus  takes  place  ;  or  to  tell  what  is  the  exact  nature 
of  its  action.  We  are  obliged,  then,  to  confine  ourselves  in  the 
main  to  considering  a  relation  between  the  vibratory  energy  of  the 
air  and  certain  states  of  consciousness,  without  attempting  to  ex- 
plain the  many  intermediate  links. 

All  sensations  which  arise  in  the  mind  by  means  of  the  irritation 
of  the  auditory  nerve  are  called  sensations  of  sound.  The  word 
"  sound  "  is  thus  used  by  psychology  for  a  wholly  subjective  affair, 
which  has  no  more  resemblance  to  those  vibrations  which  physics 
designates  by  the  same  word  than  has  the  taste  sweet  to  the  un- 
known physical  properties  that  produce  it.  The  trained  mind,  or 
"trained  ear,"  as  we  say,  has  indeed  the  power  du-ectly  to  analyze 
a  compound  musical  sound  into  its  constituent  elements.  But  each 
of  these  elements  is  purely  a  sensation,  a  subjective  affair.  It  car- 
ries in  itself  no  token  that  it  has  been  produced  by  vibrations  of 
any  kind  ;  or  that  it  sustains  any  numerical  relation  whatever  to 
the  vibrations  of  which  some  other  sensation  of  sound  is  composed. 
We  know  nothing  directly,  through  sensations,  either  of  the  struct- 

1  Die  Lelire  von  d.  Tonempfindungen  als  pliysiolog.  Grundlage  f.  d.  Tlieorie 
d.  Musik,  Braunschweig,  1st  edition,  1863;  2d  edition,  1865;  3d  edition, 
1870  ;  4th  edition,  1878. 

'^  Harmoniesystem  in  dualer  Entwicklung,  1866. 

^  Various  contributions  in  the  Archiv  f.  Ohrenheilkunde  and  elsewhere 
(especially  the  Sitzgsber.  d.  Wiener  Acad.). 

■*  Ueber  d.  Grenzen  d.  Tonwahrnehmung,  1876 ;  Sitzgsber.  d.  Jen.  Ge- 
sellsch.  f.   Med.,   1878  ;  Akustische  Untersuchungen,  1879. 

5  In  Hermann's  Handb.  d.  Physiol. ,  III. ,  il. ,  pp.  3-142,  and  works  by  the 
same  autlior  there  referred  to. 

"  Toupsychologie,  Leipzig,  1883  (Vol  I.  only). 


316  SENSATIONS    OF    SOUND. 

ure  of  the  ear  or  of  vibrating  strings  and  particles  of  air,  or  of  the 
mathematics  and  physics  of  music. 

Sounds  are  of  two  classes — tones,  or  musical  sounds,  and  noises. 
The  former  are  due  to  periodic  motions  of  sonorous  bodies  ;  the 
latter  to  non-periodic.  Noises  are  those  sounds  which,  objectively 
considered,  are  wanting  in  tlie  periodic  regularity  of  stimulation 
which  characterizes  all  musical  sounds,  and,  subjectively  considered, 
in  the  peculiar,  pleasant  modification  of  consciousness  which  the 
latter  produce.  But  noises  accompany  almost  all  tones  ;  and,  con- 
versely, tones  may  be  detected  by  the  trained  ear  as  mingled  with 
the  noises  of  every-day  life.  No  plaj'er  of  the  violin  avoids  all  noise 
of  scraping  from  the  bow  ;  no  stroke  of  a  workman's  hammer,  or 
slamming  of  a  door,  that  does  not  start  and  catch  up  into  itself 
some  trace  of  musical  tone.  The  interest  of  science  has  hitherto 
been  almost  wholly  concentrated  upon  musical  sounds,  and  little 
has  been  done  by  either  phj'sics  or  physiology  toward  tlie  analysis 
of  noises.  It  is  characteristic  of  a  noise,  according  to  Helmholtz,* 
that  there  is  a  quick  and  irregular  alternation  of  different  kinds  of 
sensation  of  sound.  This  distinctive  character  can  generally  be 
detected  "  by  attentive  aural  observation  without  artificial  assist- 
ance." "We  can  compound  noises  out  of  musical  tones  ;  as,  for  ex- 
ample, by  striking  together  all  the  keys  of  an  octave  on  the  piano. 
Hensen'"'  distinguishes  three  "  categories  of  unmixed  noises  " — the 
"  beats  "  or  pulsations  which  disturb  the  purity  of  musical  tones  ; 
the  crackle,  crack,  or  crash  ;  and  hissing  sounds.  These  three  shade 
into  each  other,  and,  when  mixed  with  different  kinds  and  quantities 
of  musical  sounds,  make  up  the  noises  which  we  hear  on  every  hand. 

§  17.  Musical  sounds  differ,  not  only  in  quality,  but  also  in 
quantity  or  intensity  of  sensation  as  dependent  upon  the  ampli- 
tude of  the  vibrations  which  produce  them.  With  respect  to  their 
qualitij  they  are  distinguished  as  either  simple  or  complex,  accord- 
ing as  they  result  from  one  set  of  regularly  recurrent  (periodic)  vi- 
brations of  a  given  number  in  a  given  unit  of  time,  or  result  from 
a  combination  of  two  or  more  sets  of  such  vibrations.  The  musi- 
cal sounds  of  ordinary  experience  are  complex.  The  blending  of 
the  simple  tones  into  the  complex  tone  is  not  so  complete,  however, 
that  it  cannot  be  at  least  partially  analyzed  directly  by  a  trained 
ear.  The  complex  sound,  which  results  from  this  compounding 
of  the  contrasts  or  coincidences  of  several  simple  musical  sounds, 
may  be  called  by  the  term  "  clang  " — in  this  meaning  borrowed 
from  the  usage  of  the  German.     The  quality  of  tones  considered  as 

1  The  Sensations  of  Tone,  etc.,  p.  11  f.     London,  1875. 

2  Hermann's  Handb.  d.  Pliysiol.,  Ill,  ii.,  p.  17. 


THE   LIMITS    OF   PITCH.  317 

simple  sensations  is  their  pitch,  which  varies  according  to  a  scale  of 
states  of  consciousness  that  are  immediately  apprehended  and  com- 
pared with  each  other,  and  that  are  discovered  by  objective  meth- 
ods to  correspond  to  a  scale  of  changes  in  the  number  of  the  vi- 
brations of  the  waves  which  occasion  them.  The  pitch  of  tones  is 
therefore  spoken  of  as  "high"  or  "low,"  according  to  the  place 
which  we  assign  to  the  resulting  sensations  in  this  scale.  Such 
place  in  the  scale  may  be  considered  either  with  respect  to  the  re- 
lation of  any  particular  tone  to  the  upper  or  lower  limits  of  the 
scale,  or  with  respect  to  the  relation  of  the  different  tones  to  one 
another.  "  Clangs,"  or  complex  tones — the  musical  sounds  with 
which  we  are  made  acquainted  by  all  ordinary  experience — have 
also  a  variable  quality  called  timbre,  or  "  color-tone  ;  "  the  timbre 
of  the  clang  is  dependent  upon  the  pitch,  number,  and  relative  in- 
tensity of  the  simple  tones  which  compose  it.  Thus  a  note  having 
the  same  place  in  the  musical  scale  (for  example,  a  of  the  once- 
marked  octave — 440  vibrations)  sounds  differently,  as  we  say,  on 
the  piano,  violin,  cornet,  or  when  sung  hy  the  human  voice.  The 
pitch  of  the  tone  as  produced  by  all  these  different  methods  is  the 
same  ;  but  its  color-tone  is  determined  by  the  character  of  the 
over-tones  which  are  blended  with  the  fundamental  tone. 

§  18.  Tlh.Q  pilch  of  tones  depends  npon  the  rapidity  of  the  peri- 
odic vibrations  (the  number  in  a  given  unit  of  time — usually  one 
second)  wliich  occasion  them,  or — what  is  the  same  thing — upon 
the  length  of  the  sound-waves.  This  class  of  sensations,  however, 
has  both  an  upper  and  a  lower  limit ;  that  is  to  say,  vibrations  ei- 
ther below  or  above  a  certain  number  per  second,  or — what  is  the 
same  thing — -wave-lengths  that  are  either  shorter  or  longer  than  a 
given  limit,  produce  no  sensations  of  musical  sound.  The  difficulty 
of  determining  these  limits  is  great,  because  the  intensity  of  ex- 
tremely low  or  high  tones  has  to  be  enormously  increased  in  order 
that  the}^  may  be  heard  at  all  ;  because  the  perceptions  of  the 
acoustic  sense  are  so  very  blunt  near  the  limits  that  the  different 
sensations  are  almost  certain  to  be  confused  ;  because  distracting 
sensations  of  common  feeling  mingle  in  these  ranges  of  tone  with 
the  sensations  of  sound,  and  because  near  the  lower  limits  the 
over-tones — especially  the  octave  above — become  so  strong  as  to  be 
mistaken  for  the  fundamental  tones.  On  account  of  these  diffi- 
culties the  older  investigators  made  numerous  mistakes.  Indi- 
vidual j)eculiarities  are  also  very  important  in  determining  sensa- 
tions of  pitch.  Some  persons  can  hear  tones  below  or  above  those 
audible  to  most  others.  Helmholtz  '  thought  that  sensations  of 
'  The  Sensations  of  Tone,  p.  268.     London,  1875. 


318 


SENSATIONS   OF   SOUND. 


tone  begin  to  cease  when  the  vibrations  fall  below  34  per  second  ; 
some  tuning-forks  of  great  size,  which  vibrated  only  28  times  per 
second,  seemed  to  him,  however,  to  have  a  trace  of  tone  in  the  form 
of  a  "weak  drone."  Preyer '  found  that  while  14  vibrations  pro- 
duced no  tone  that  he  could  hear,  at  16  vibrations  he  was  able  to 
hear  a  tone  ;  others  could  distinguish  a  musical  sound  only  at  19 
or  23  vibrations.  The  same  observer  experienced  as  a  sensation  of 
musical  sound  more  than  40,000  vibrations  per  second  ;  Turnbull 
found  that  the  majority  of  those  with  whom  he  experimented 
could  not  hear  more  than  about  20,000  to  22,500  vibrations  per  sec- 
ond, and  only  one — a  musician — heai'd  30,000  ;  Despretz  succeeded 
in  producing  with  tuning-forks  audible  tones  that  had  32,000  vi- 
brations. Blake  thinks  that  persons  with  defective  ear-drums  are 
able  to  hear  tones  of  higher  pitch,  reaching  even  50,000  vibrations. 
Vibrations  slower  than  28  to  30  per  second  produce  in  most  ears 
only  a  buzzing  or  groaning  sound  ;  the  more  acute  tones  are  unpleas- 
ant, or  even  painful,  and  finally  inaudible  to  all  ears.  These  results 
cannot  be  considered  as  very  concordant  or  precise.  They  show, 
however,  that  the  range  of  the  average  human  ear  is  rather  more 
than  nine  octaves,  reaching  from  about  A„_  of  the  sub'contra  octave 
(27-j  vibrations  per  second)  to  above  c'  of  the  seven-times-marked 
octave  (16,896  vibrations  per  second). 

The  following  table "  gives  the  pitch  of  all  the  musical  tones  audi- 
ble to  the  human  ear,  in  the  key  of  C  major,  on  a  scale  in  which 
a'  is  fixed  at  440  vibrations.  Only  about  seven  of  the  rather  more 
than  eleven  octaves  of  the  table  are,  however,  usable  in  music  ; 
these  seven  reach  upward  from  C ^  of  the  contra,  or  fz-om  A„  of  the 
subcontra  octave,  to  6^ — namely,  the  seven  or  seven  and  a  half 
octaves  of  the  modern  piano. 


c 


D 


E 


B 


Subcontra  octave 

Contra  octave  

Great  octave 

Small  octave 

Once-marked  octave     

Twice-marked  octave 

Thrice-marked  octave 

Four-times  marked  octave 
Five-times-marked  octave  . 
Six-timt-s-marked  octave  .. 
Sevcii-timcs-marked  octave 
Eight-times-iiiarked  octave 


33 

6H 

132 

2(i4 

528 

1.056 

2,112 

4.224 

8.44S 

16,S9fi 

33,792 


18%  6 

3T'^ 

74  J:^ 

1481^ 

297 

594 

1,188 

2,376 

4,752 

9,504 

19,(108 

38,016 


20% 

41 H 

S2M 

16> 

330 

660 

1,320 

2,640 

5.280 

10.560 

21,1-iO 

42,240 


22 

24i'i 

27^ 

44 

49j<r 

55 

88 

99 

110  , 

176 

198 

220 

352 

396 

440  ! 

704 

792 

880  i 

1,408 

1,584 

1,760  ' 

2.816 

3,168 

3,520  ; 

.'5.6.32 

6,336 

7,040 

11,264 

12.672 

14.080 

22.528 

25,344 

28.160 

.3015/,,  Cj 

fil^  C, 

123?^  ;  c. 

2473<?  :  c, 

495  c', 

990  c2 

1,980  cs 

3,960  o^. 

7,920  c6, 

15,840  c6, 

31.680  c'i 


,  T>2,  etc. 
,  Dj,  etc. 

D,  etc. 
(i,  etc. 
,  d',  etc. 
,  d2,  etc. 
,  d'i,  etc. 

d",  etc. 
,  d^,  etc. 

d^,  etc. 
.  d^,  etc. 


'  Grenzen  d  Tonwahrnehmiiiig,  p.  23  f. 

-  Taken  from  Stumpf,  Tonpsychologie,  I.,  p.  xiv. ,  and  giving  the  German 
scale  ;  tlie  Frencli  fixes  a'  at  435  vibrations  ;  the  theoretical  pitch  in  England 
gives  512  for  c'K 


SENSITIVENESS  TO   PITCH.  319 

§  19.  The  sensitiveness  of  the  ear  to  differences  of  pitch  varies 
greatly  with  different  individuals,  and  for  the  different  octaves  of 
the  musical  scale.  Preyer  found  that  unpractised  persons,  within 
the  octaves  from  c  to  c^  (132-1,056  ^dbrations  by  the  table,  but 
128-1,024  by  the  scale  adopted  for  his  experiments),  distinguish 
a  difference  of  from  8  to  16  vibrations  as  producing  a  distinct  dif- 
ference in  the  sensation  of  pitch.  Extreme  cases  of  deafness  to 
differences  in  pitch  are  recorded  ;  as,  for  example,  that  of  the  man' 
who,  in  the  middle  part  of  the  scale,  could  not  distinguish  an  in- 
terval of  less  than  a  third,  and,  in  the  higher  and  lower  parts,  of 
less  than  a  seventh.^  Persons  insensitive  to  differences  of  a  tone  or 
half-tone,  who  are  sometimes  said  "not  to  know  one  note  from 
another,"  are  by  no  means  infrequently  met  with.  Differences  of 
the  two  ears  of  the  same  person,  in  the  fineness  of  this  kind  of  per- 
ception, are  common  enough  ;  in  certain  cases  the  difference  may 
amount  to  a  half-tone  or  more.  Sensitiveness  to  pitch  is  generally 
capable  of  rapid  cultivation,  and  may  reach  a  high  degree  of  per- 
fection in  persons  Avho  have  what  is  called  "  a  good  natural  ear"  for 
musical  tones,  if  the  ear  be  also  highly  trained.  Such  persons  may 
become  able  to  discriminate  differences  in  the  sensations  caused  by 
changing  the  number  of  vibrations  not  more  than  a  third  of  a  single 
vibration  per  second,  in  the  region  of  the  scale  between  a'  and  c'. 
In  the  octave  from  6'  to  h'  more  than  200  tones  are  distinguish- 
able. But  above  and  below  this  region  the  distinctions  jDos-sible 
are  less  fine  ;  above  c^  even  well-trained  ears  commit  errors  in  iden- 
tifying two  notes  that  differ  by  100  or  even  by  1,000  vibrations.  It 
appears,  then,  that  not  only  the  musical  quality  of  tones,  but  also 
the  power  of  distinguishing  differences  in  them,  diminishes  rapidly 
as  we  approach  the  upper  and  lower  limits  of  the  scale. 

The  fineness  of  the  possible  distinctions  of  purity  of  interval  also 
differs  for  different  individuals  and  for  different  intervals.  The 
following  table  is  compiled  by  Hensen  ^  from  data  drawn  from 
Preyer 's  investigations.  The  bracketed  numbers  of  the  first  column 
indicate  the  proportion  in  which  the  vibrations  of  the  different 
intervals  stand  to  those  of  the  fundamental  tone  ;  the  quotient 
n  :  n  =  i,  the  variation  from  the  pure  interval  which  was  fovind 
detectable  in  each  case  ;  V  =  the  number  of  vibrations  off  from  the 
pure  interval  which  is  the  least  distinguishable  ;  and  aS"  is  the  de- 

1  Reported  by  Grant  Allen,  in  Mind,  1878,  p.  157  f. 

^  Comp  the  lengthy  and  interesting  discussion  on  "Individualitat  des  Sin- 
nes  und  Gedachtnisses  fiir  Tonqualitaten,"  in  Stumpf,  Tonpsychologie,  I.,  pp. 
263  ff. 

''See  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  114. 


320 


SENSATIONS    OF    SOUND. 


nominator  of  the  fraction  which  indicates  the  sensitiveness  of  the 
ear  to  the  purity  of  each  interval. 


rNTERVAL. 


Fourth  (1.333) 

Fifth  (1.5) 

Minor  Sixth  (1.6) 

Major  Third  (1.25) j 

Minor  Third  (1.20) , 

Octave  (2.0) 

V/holeTone  (1.125) 


n. 

n' . 

i. 
1.3396 

V. 

187.58 

251.23 

1.02 

167.68 

251.23 

1.4983 

0.23 

143.06 

231.41 

1.6108 

1.19 

139.60 

163.68 

1.2437 

0.73 

139.62 

175.53 

1.2572 

0.89 

207.54 

251.23 

1.2102 

1.90 

500.40 

1,001 

2.0004 

0.13 

215.15 

243.51 

1.1291 

0.85 

211 

822 
148 
198 
193 
117 
5,000 
274 


Immediate  judgment  of  abf;ohUe  tone  (as  the  «'  carried  in  mind 
by  musicians)  is  possible  ;  judgment  between  two  tones  as  to 
which  is  higher  or  lower  in  pitch  is  also  immediate,  and  may  be 
exercised  independently  of  everything  except  the  two  sensations 
themselves.  The  latter  judgment  is  the  common  power  of  mind 
belonging  to  this  sense  ;  the  former  is,  as  a  rule,  exercised  only  by 
skilled  persons,  and  by  them  only  very  imperfectly.  Experiments 
of  Stumpf,'  upon  himself  and  three  other  musicians,  showed  that 
the  mistakes  in  judgment  of  absolute  tone  amounted,  in  the  lower 
region  of  the  scale  (from  G^  to  B^),  to  15^-100^  of  the  trials  ;  in 
the  middle  region  (from  a-cj\  or  from  g-e'),  to  Qfo-lQ'fo  ;  in  the 
ujjper  region  (from  g'^-f'^,  or  from/^-a^),  to  7^-80^^.  Only-one  of 
the  four  persons  experimented  upon  seemed  to  approach  the  point 
of  infallibility.  Judgment  of  absolute  tone  is,  therefore,  a  different 
matter  from  that  which  makes  distinctions  in  intervals  or  in  the 
least  observable  differences  of  pitch,  and  is  much  more  precarious. 

§  20.  Those  psychologists  appear  to  be  in  the  right  who  claim 
that  some  power  of  the  mind  immediately  to  judge  differences  of 
quality  in  pitch,  purely  as  such,  must  be  assumed  in  order  to  ac- 
count for  the  foregoing  phenomena."  Such  judgment,  however, 
may  be,  and  ordinarily  is,  much  assisted  by  auxiliary  discrimina- 
tions of  other  sensations  which  blend  with  those  of  musical  tone. 
Among  such  secondary  helps  the  most  important  are  the  muscular 
sensations  which  accompany  the  innervation  of  the  larynx  and  other 
organs  used  in  producing  musical  tones.     For  we  ordinarily  inner- 

'  Ton p.sychol ogle,  I.,  pp.  305  ff. 

s  On  tin's  Rubiect.  comp.  Lotze,  Medicin.  Psychologie,  pp.  265  ff.,  480  f.  ; 
Strieker,  Studien  iiber  d,  Association  d.  Vorstellungen,  1883.  p.  2  1;  G.  E. 
Miiller,  Zur  Grundlftcung  d.  Psycho-physik,  Berlin,  1878,  pp.  276  ff.;  and 
Stumpf,  Toupsychologie,  I.,  pp.  134  ff. 


THE   JUDGMENT   OF   TONES.  321 

vate  these  organs  (at  least  in  an  inchoate  and  partial  way) — that  is, 
"we  sound  the  note  to  ourselves — when  trying  carefully  to  judge  of 
its  pitch.  But  the  niceness  of  these  muscular  sensations  is  not 
great  enough,  even  when  most  highly  trained,  to  account  for  the 
discriminations  of  the  "  good  ear."  The  trained  musician  can  de- 
tect by  ear  a  difference  in  quality  between  two  tones  of  400  and 
400^  vibrations  per  second  ;  but  the  most  skilful  singer — Jenny 
Lind,  for  example — scarcely  succeeds  in  singing  in  quarter-tones. 
Moreover,  the  relative  powers  of  larynx  and  ear  by  no  means  keep 
pace  with  each  other  in  the  same  person.  It  should  also  be  re- 
membered that  all  our  ordinary  discriminations  of  musical  sound 
apply  to  composite  tones,  or  "  clangs  ;  "  in  discriminating  these  we 
are  aided  by  the  color-tone,  or  tone-feeling,  which  belongs  to  each 
note  as  sounded  by  some  sonorous  body  with  whose  peculiarities 
we  are  previously  more  or  less  acquainted. 

It  follows,  then,  that  the  judgment  is  supplied,  by  the.  varying 
qualities  of  musical  tones,  with  the  means  for  arranging  them  in  a 
continuous  series  which  may  be  symbolized  by  different  positions 
assigned  along  an  uninterrupted  straight  line.  Of  any  three  un- 
like tones,  one  must  be,  and  only  one  can  be,  arranged  as  respects 
pitch  between  the  other  two.  And  whenever  any  two  tones,  as  m 
and  n,  are  given,  another  sliding  tone,  which  begins  with  m  and 
ends  with  «,  is  possible.  Moreover,  within  the  bounds  of  our  ex- 
perience of  tones,  as  we  advance  along  the  scale  toward  either  the 
upper  or  the  lower  limit,  we  see  no  tendency  in  the  qualities  of 
the  sensations  to  approach  each  other.  In  this  respect  the  scale 
of  sound-tones  is  wholly  different  from  that  of  color-tones.  There 
are  not  two  ways,  for  example,  of  getting  from  a'  to  c^  (one 
through  b\  c^  etc.,  and  the  other  through  g\  f,  etc.,  around  to 
e\  d,^  and  then  c"),  as  there  are  two  ways  of  going  from  yellow  to 
blue  (i.e.,  through  green  and  blue-green,  or  through  violet,  red, 
and  orange).  We  speak,  then,  of  the  series  of  tones  as  a  constant 
and  infinite  series  ;  although,  of  course,  no  series  of  states  of  con- 
sciousness is  really  infinite,  and  although  the  upper  and  lower 
limits  of  the  musical  scale,  as  well  as  the  limits  of  the  least  ob- 
servable differences  between  two  tones,  are  not  constant  but  vari- 
able for  different  individuals. 

The  symbolism  taken  from  relations  of  space,  which  we  employ 
when  we  speak  of  certain  acoustic  sensations  as  "  high "  and  of 
others  as  "low"  in  pitch,  or  when  we  distinguish  so-called  "in- 
tervals "  between  the  tones  as  large  and  small,  is  strictly  applicable 
only  to  the  complex  tactual,  visual,  and  muscular  sensations  that 

accompany  the  acoustic.      In  sounding  the  lower  tones  with  the 
31 


322  SENSATIONS   OF   SOUND. 

voice  the  organs  are  depressed  ;  in  sounding  the  higher,  they  are 
elevated.  Low  notes  have  a  certain  breadth  and  gravity  which 
corresponds  to  the  foundations  of  a  spatial  structure  ;  as  sensations 
they  require  more  time  to  come  into  and  depart  from  conscious- 
ness, as  it  were.  A  great  intensity  and  slower  tempo  belong  to  the 
bass-viol  than  to  the  violin.  We  read  iqj  for  the  notes  of  highest 
pitch,  and  doivn  for  those  of  lowest  pitch,  in  the  written  musical  scale. 
§  21.  We  have  seen  that  tones,  like  rays  of  light,  come  to  us  as 
compounded  into  "clangs;"  these  really  composite  tones  being 
esteemed  as  single  notes  in  ordinary  experience.  The  nature  of 
such  composition  determines  the  so-called  "timbre,"  or  "color- 
tone,"  of  the  notes.  Each  sensation  of  a  clang  is  a  summing-up  in 
consciousness  of  several  absolute  qualities  of  musical  sound  ;  the 
stimulus  which  occasions  this  complex  subjective  state  is  a  complex 
sound-wave  made  up  of  the  contrasts  and  coincidences  of  several 
single  waves  that  have  the  character  of  simple  pendulum  vibrations. 
The  quality  of  each  clang  depends  upon  the  form  of  this  complex 
sound-wave.  We  need  not  consider  in  detail  the  physics  and 
mathematics  of  such  complex  waves.  It  is  enough  to  observe  that 
those  single  tones  whose  vibrations  stand  in  simple  mathematical 
relations  to  each  other,  when  combined  into  a  clang,  cause  a  pe- 
culiarly pleasant  sensation  ;  those  whose  vibrations  stand  in  com- 
plex mathematical  relations  make,  when  combined,  an  unpleasant 
sensation.  In  an  octave  of  the  musical  scale  the  eight  different 
notes  stand  in  the  following  ratios  to  each  other.' 


D  :  E 

9  .  5. 

¥  •  4 

9  :  10 


F 


101 


G 

:    A 

:    B 

:    C 

3 

2" 

.       .5 
•       3 

¥- 

2 

12 

^.\^ 

15 

16 

That  is  to  say,  while  the  tone  G  makes  one  vibration,  D  makes 
nine-eighths,  and  E  makes  five-fourths,  etc.  ;  or  while  G  makes  8 
vibrations  D  makes  9,  E  makes  10,  etc.  Of  these  relations  in  the 
number  of  vibrations  the  simplest  is,  of  course,  that  of  the  octave, 
1  :  2.  The  acoustic  waves  which  constitute  the  stimuli  of  each 
complex  sensation  called  a  "  clang,"  accordingly,  also  permit  of 
being  regarded  as  the  summing-up  of  the  waves  of  a  fundamental 
tone  and  of  certain  partial  tones  belonging  to  the  fundamental 
tone.  These  partial  tones,  or  "over-tones,"  are  called  "the  har- 
monics" of  the  "  clang,"  or  single  compound  tone. 

§  22.  When  two  or  more  "clangs "are  sounded  together,  the  re- 
sult is  what  is  called  either  a  "chord  "  or  a  "  discord."     The  former 

1  For  the  mathematics    and   physics  of   tones,  see  Hensen,  in  Hermann's 
Handb.  d.  Physiol.,  III.,  ii  ,  pp.  4fE. 


CONSONANCE   AND   DISSONANCE.  323 

is  a  pleasant,  tlie  latter  an  unpleasant,  complex  of  sensations  ;  con- 
sonance and  dissonance  are  thus  spoken  of  as  qualities  of  sensations 
of  musical  sound.  Thus,  if  c  and  c'  are  struck  together  upon  a 
weil-tuued  piano,  the  combination  of  clangs  is  a  chord,  or  harmo- 
nious musical  sound  ;  but  if  c  and  d,  or  c  and  c  sharp,  or  c  and 
its  seventh,  h  above,  are  simultaneously  sounded,  then  the  com- 
bination of  tones  is  unpleasant.  Cases  of  consonance  and  disso- 
nance differ  from  those  just  considered  under  the  term  "clang" 
only  with  respect  to  the  relative  strength  of  the  partial  tones  as 
compared  with  the  fundamental  tones :  in  the  clang  the  over-tones 
are  weak  as  compared  with  the  one  fundamental  tone  ;  but  in  the 
chord  or  discord  the  fundamental  tones  of  the  other  clangs  are,  of 
course,  strong,  and  stand  in  powerful  relations  of  consonance  or 
dissonance  both  toward  the  fundamental  tone  of  the  lowest  clang 
and  toward  its  partial  tones.  All  the  partial  tones  of  the  different 
combined  clangs  enter  into  the  formation  of  the  total  result  pro- 
duced. According  to  the  table  already  given  (p.  322),  the  Octave 
is  the  most  perfect  possible  consonance  (1  : 2);  then  the  Twelfth 
(1 : 3),  the  Fifth  (2  :  3),  the  Fourth  (3  : 4),  the  Sixth  (3  :  5),  the  ma- 
jor Third  {4  :  5),  the  minor  Third  (5  :  G).  With  the  relation  of  the 
Third  we  come  upon  the  borders  of  dissonance  ;  indeed,  the  ancient 
Greeks  and  Komans  considered  the  Third  a  dissonance,  and  avoided 
it  in  singing,  because,  as  Helmholtz  supposes,  their  ears  were  more 
sensitive  to  "beats "  than  ours.  The  consonance  of  the  Sixth  and  that 
of  the  Fourth  have  also  been  much  disputed.  The  major  Sixth 
and  major  Third  are  called  by  Helmholtz  "  medial  consonances  ; " 
the  minor  Third  and  minor  Sixth,  "imperfect  consonances." 

An  analysis  of  the  harmonics  of  these  consonances  yields  the  fol- 
lowing results,'  which  show  the  amount  of  coincidence  belonging 
to  the  acoustic  waves  of  the  different  tones  when  combined  in  a 
chord  with  a  fundamental  tone. 

Octave  j"'g'"'"'g'^^°"' 
(  c'  I    c'^       g'        c'^ 

Twelfth  ]«l-^:il^l^V^^!^li!. 


Fifth  j 


Fourth 


Major  Third  |  ° 
(  e 


c'  g'  c-  e- 


gi     d'^ 
ci  g'  c'  e^ 


c^  g'  c'^ 


b'  e'^ 

The  major  Sixth  is  similar  in  the  form  of  its  harmonics  to-  the 
major  Third. 

'  Conap.  Helmholtz,  The  Sensations  of  Tone,  p.  281  f. 


324  SENSATIONS   OF   SOUND, 

Two  psycho-physical  causes  for  the  characteristic  feelings  which 
belong  to  sensations  of  consonance  and  dissonance,  respectively, 
may  be  assigned  with  more  or  less  of  probability.  The  first  is  that 
proposed  by  Helmholtz.'  The  feeling  of  dissonance  which  is  pro- 
duced by  sounding  together  two  notes  that  differ  only  by  a  semi- 
tone is  found  to  be  increased  when  the  difference  in  the  pitch  of 
the  notes  is  still  further  diminished.  Successive  shocks  called 
"beats  "  occur,  less  frequently  but  more  decidedly  and  unpleasantly, 
as  the  pitch  of  the  notes  becomes  more  nearly  the  same.  The  feel- 
ing of  dissonance  is  found  to  reach  its  height  when  the  number  of 
beats  is  about  30  per  second.  For  example,  if  6'  (495  vibrations) 
and  c^  (528  vibrations)  are  struck  together,  the  number  of  beats 
is  33  (528  —  495=33),  and  the  dissonance  is  very  strongly  marked. 
In  all  marked  dissonances  such  beats  occur  at  the  rate  of  from  20 
to  40  in  a  second.  The  unpleasant  effect  in  consciousness  is  an- 
alogous to  that  produced  by  all  sudden  and  rapid  intermission  of 
stimulation  ;  as,  for  example,  the  flickering  of  light  or  the  scraping 
of  uneven  surfaces  over  the  skin.  The  feeling  of  consonance  is  due 
to  the  absence  of  beats.  In  addition  to  Helmholtz's  negative  reason, 
Oettingen  has  jDroposed  the  positive  one,  that  the  pleasantness  of 
harmony  is  due  to  what  he  calls  the  "  tonicity  "  and  "  phonicity  " 
of  certain  intervals  and  combined  notes.  "  Tonicity  "  is  the  prop- 
erty of  being  recognized  as  a  constituent  of  a  single  fundamental 
tone  which  is  designated  by  the  name  "tonic."  "Phonicity"  is 
that  property  of  a  chord  or  interval  which  consists  in  the  possession 
of  certain  partial  tones  that  are  common  to  all  tones.  The  first  of 
these  qualities  of  harmony  seems  to  ally  the  pleasure  it  yields  to 
that  which  follows  even  the  obscure  and  only  half-conscious  per- 
ception, as  it  were,  of  all  relations,  as  such,  between  our  sensa- 
tions. 

§  23.  In  order  that  the  physical  apparatus  of  hearing  may  act 
as  the  organ  of  those  wonderfully  fine  discriminations  which  belong 
to  the  most  analytic  of  all  the  senses,  it  would  seem  that  it  must 
possess  an  outfit  of  end-organs  with  structure  sufficiently  minute 
to  serve  as  a  basis  for  a  satisfactory  development  of  "local  signs." 
The  number  of  the  cells  of  Corti,  and  of  their  separate  terminal 
auditory  nerves,  has  been  calculated  by  Hensen  '^  at  about  16,400 ; 
by  Waldeyer '  at  20,000.  It  is  doubtful,  howevei^  whether  even 
this  large  number  will  suffice  to  account  for  that  niceness  of  audi- 
tory discriminatioDS  which  we  have  seen  to  be  possible. 

'  The  Sensations  of  Tone,  p.  255  f. 

■^  In  Hermann's  Handb   d.  Physiol,  III.,  ii.,  p.  115. 

^  Strieker  s  Gev,ebelehre,  II.,  p.  954. 


CHAPTEE  lY. 
THE  QUALITY  OF  SENSATIONS.     [Continiied.] 

§  1.  The  analysis  of  the  qualities  of  different  Sensations  of  Sight 
is  much  more  intricate  than  that  of  any  of  the  other  senses.  They 
may  all  be  described  as  sensations  of  color  and  light ;  but  an  in- 
definite number  of  colors  is  known  to  experience,  and  as  many 
grades  of  the  sensation  of  light.  Moreover,  the  quantity  of  the 
white  light  which  acts  as  stimulus  upon  the  eye  has  an  important 
effect  upon  the  quality  of  the  resulting  color-sensation  ;  in  other 
words,  the  tone  of  the  color  is  dependent  upon  the  amount  of  white 
light  which  is  mixed  with  the  "  saturated  "  spectral  color.  The  size  of 
the  colored  object  and  the  resulting  breadth  of  the  sensation,  as 
well  as  the  intensity  of  the  stimulus  and  the  time  during  which  it 
acts,  also  affect  the  quality  of  the  sensation.  Still  further,  the  same 
stimulus  produces  different  sensations  as  it  falls  upon  different  por- 
tions of  a  normal  retina  ;  while  a  considerable  class  of  persons  are 
color-blind,  or  incapable  of  certain  kinds  of  color-sensations.  The 
previous  condition  of  the  retina,  and  the  relations  between  the  con- 
tiguous portions  when  any  considerable  area  of  it  is  under  stimu- 
lation, must  also  be  taken  into  account.  The  fundamental  laws 
governing  sensations  of  sight  can,  therefore,  be  discovei'ed  only  by 
excluding  for  the  time  many  of  those  variable  elements  which,  in 
fact,  always  enter  into  the  determination  of  the  exact  quality  of 
such  sensations.  Thus  defining  the  first  problem  before  us,  we 
find  that  it  may  be  stated  in  the  following  terms.  What  sensations 
result  from  the  stimulation  of  a  sufficiently  small,  but  not  too  small, 
area  of  the  most  central  part  of  a  normal  retina,  for  a  given  time, 
when  it  is  not  fatigued  and  the  eye  is  at  rest,  and  with  neither  too 
great  nor  too  small  intensity  of  a  given  kind  of  light?  Such  sen- 
sations may  be  called  (though  somewhat  ineptly)  normal  sensations 
of  color.  When  the  foregoing  question  is  answered  we  may  go 
on  to  consider  the  most  important  variations  possible  on  account 
of  various  forms  of  departure  from  the  so-called  normal  conditions 
of  sensation. 

§  2.  The  ordinary  stimulus,  the  application  of  which  to  the  eye 
gives  rise  to  the  sensations  of  sight,  is  light — or  certain  exceedingly 


326  SENSATIONS   OF   SIGHT. 

rapid  oscillations  of  luminiferous  ether.  Some  forms  of  mechani- 
cal and  electrical  stimuli  also  produce  the  same  sensations.  Any 
violent  shock  to  the  eye,  such  as  a  blow  upon  the  back  of  the  head, 
maj^  fill  the  whole  field  of  vision  with  an  intense  light.  The  action 
of  mechanical  pi*essure  of  moderate  intensity  upon  a  limited  j^art 
of  the  retinal  elements  may  be  studied  by  rolling  the  eyeball  in- 
ward and  using  the  fingernail,  or  a  small,  blunted  stick,  upon  the 
outer  surface  of  the  closed  lids.  By  such  stimulation  disks  of 
light  (called  2^hosphenes),  with  darkly  colored  edges,  are  produced 
in  the  field  of  vision  of  the  closed  eye.  Some  observers  have 
claimed  that  very  strenuous  exertion  of  the  apparatus  for  accom- 
modation occasioned  in  their  eyes  similar  phenomena  ("phos- 
phenes  of  accommodation  ").  On  making  or  breaking  a  weak  elec- 
trical current  sent  through  the  eye,  the  entire  field  of  vision  is 
lighted  up  ;  the  constant  current  also  seems  to  excite  the  optic 
nerve.  The  quality  of  the  sensations  thus  excited  is  found  to  de- 
pend upon  the  direction  of  the  current  through  the  nerve.  When 
the  current  is  ascending,  the  place  where  the  nerve  enters  the  ret- 
ina appears  as  a  dark  disk  upon  a  field  of  vision  that  is  bright- 
er than  it,  and  of  pale  violet-color  ;  when  it  is  descending,  as  a 
bright  bluish  disk  on  a  field  of  dark  or  reddish-yellow  color.  The 
retina  has  also  a  "  light  of  its  own  "  {Eigenlicht)  ;  for  its  nervous 
elements  are  rarely  or  never  inactive,  but  have  a  continuous  tonic 
excitation.  Hence  the  most  gorgeous  and  varied  coloring  is  often 
seen  when  the  eyes  are  closed  in  a  darkened  room.  This  normal 
light  of  the  retina  is  not  constant  either  in  degree  or  in  quality  ; 
both  the  form  and  the  color  of  the  different  minute  parts  of  the 
field  of  vision,  as  lighted  by  it,  are  very  changeable.  It  may  be 
said  to  have  the  rhythmic  movement  of  all  tonic  excitation.  Such 
excitation  is  supposed  to  be  due  to  chemical  effects,  wrought  by 
the  changing  supply  of  blood,  upon  the  nervous  elements  of  the 
retina  and  (perhaps,  also)  of  the  central  organs  of  the  brain.  The 
peculiar  action  of  the  ascending  and  descending  electrical  current 
has  been  thought  by  some  '  to  be  due  to  its  catelectrotonic  or 
anelectrotonic  effect  upon  the  central  organs  by  way  of  the  optic 
nerve.  Aubert  has  estimated  the  retina's  own  light  to  be  about 
equal  (in  his  case)  to  half  the  brightness  of  a  sheet  of  white  pajier 
when  seen  in  the  full  light  of  the  planet  Venus. 

§  3.  The  place  where  the  light  acts  (and  here,  as  is  supposed,  only 
indirectly  through  photo-chemical— and  perhaps  electro-motive — 
changes  in  the  pigments  of  the  eye)  upon  the  end-organs  of  vision 

'  See  Fick,  Physiolog.  Optik,  iu  Hermann's  Handb.  d.  Physiol.,  III.,  i. ,  p 
230. 


THE   FINElSrESS   OF   VISION. 


327 


must  be  located  at  the  back  of  the  retina  in  the  rods  and  cones 
(see  Part  I.,  Chap.  V.,  §§  18-22).  The  argument  b}'  which  we  have 
connected  the  analytic  power  of  vision  with  the  structure  of  this 
nervous  layer  ma}'  be  carried  yet  further  into  details.  It  appears 
likely  that  each  element  of  the  structure — at  least  in  some  parts  of 
the  retina — should  be  regarded  as  an  isolated  sensitive  spot,  which 
corresponds  on  the  one  side  to  definite  excitations  from  the  appro- 
priate stimuli,  and  on  the  other  side  to  the  smallest  localized  sen- 
sations of  color  and  light.  In  order  that  two  visual  sensations 
may  be  seen  as  separate,  yet  side  by  side,  in  an  object,  two  neigh- 
boring retinal  elements  must  be  excited  by  the  stimulus.  This 
implies  that  the  breadth  of  retinal  surface  stimulated  must  be,  at 
least,  about  that  of  the  distance  between  two  such  elements.  With 
this  hypothesis  the  facts  of  histology  and  exi^erimental  physiology 
agree  fairly  well. 

The  degree  of  accuracy  which  sight  can  attain  is  dependent 
upon  the  size  of  the  retinal  elements  directly  affected  by  the 
light. '  Hooke  observed  that  no  one  can  distinguish  two  stars  as 
two,  unless  they  are  apart  at  least  30"  ;  few,  indeed,  can  distin- 
guish them  when  less  distant  from  each  other  than  60'.  E.  H. 
Weber  could  not  perceive  as  separate  two  lines  whose  distance 
did  not  cover  at  least  73"  of  the  angle  of  vision  ;  Helmholtz  puts 
the  limit  of  his  sharpness  of  vision  at  64".  The  numbers  60", 
64",  and  73",  in  the  angle  of  vision,  correspond  to  a  size  of  the 
retinal  elements  varying  from  0.00438  mm.  to  0.00526  mm.;  and 
this  agrees  very  closely  with  the 
calculated  breadth  (by  Kolliker) 
of  the  thickness  of  the  cones  in 
the  yellow-spot — namely,  0.0045 
mm.  to  0.0055  mm.  (0.000177  in. 
to  0.0002165  in.}.  If  white  lines 
be  drawn  on  a  dark  ground  so 
closely  together  as  to  approximate 
this  limit  of  vision,  they  will  ap- 
pear, not  straight,  but  knotted  and 
nicked.  This  fact  is  due  to  the 
action  of  the  stimulus  on  the  mo- 
saic of  rods  and  cones,  as  seen  by  the  accompanying  figure  (No.  90). 
The  diminishing  sharpness  of  vision  as  we  move  away  on  the  sur- 
face of  the  retina  from  its  most  central  area  corresponds  to  the 

'  See  Helmholtz,  Handb.  d.  Physiolog.  Optik,  Leipzig.  1867,  p.  215  ft.; 
Fick,  in  Hermann's  Handb.  d.  PhjsioL,  HI.,  i.,  p.  152  f.;  von  Kries,  ArcMv 
f.  Anat.  u.  Physiol.,  Physiolog.  Abth.,  1883  (Appendix),  p.  24  f. 


Fig.  90. — A  shows  the  appearance  of  lines 
drawn  veiy  clopely  together,  which  is  sup- 
posed to  be  due  to  their  falling  upon  the 
nervous  elements  of  the  retina  in  the  man- 
ner shown  by  B. 


328  SENSATIONS    OF   SIGHT. 

comparative  paucity  of  the  nervous  elements  which  enter  into  the 
structure  of  the  peripheral  parts. 

§  4.  Excluding  consideration  of  those  changes  in  the  quantity, 
as  such,  of  visual  sensations  which  are  produced  by  changes  in  in- 
tensity of  the  light,  and  confining  our  attention  to  what  has  already 
been  defined  as  the  normal  action  of  the  eye  (comp.  p.  325),  we  treat 
scientifically  all  the  different  sensations  of  sight  when  we  describe 
(1)  the  wave-lengths  of  the  different  kinds  of  colored  light,  or  pure 
color-tones,  and  (2)  the  relations  in  which  the  different  colors 
stand  with  respect  to  the  amounts  of  white  (or  colorless  light)  and 
saturated  light  (or  light  of  pure  color-tone)  which  enter  into  them. 
The  foregoing  distinctions  in  the  quality  of  our  color-sensations 
may  be  confirmed  by  an  appeal  to  experience.  Eed  is  unlike  yellow 
in  "color-tone,"  and  both  are  unlike  blue  ;  but  orange  is  more  like 
either  red  or  yellow  than  it  is  like  blue,  while  violet  is  more  like 
blue  than  it  is  like  either  yellow  or  red.  Yet  we  distinguish  colors 
of  the  same  class  (red,  green,  or  violet)  as  being  like  or  unlike 
with  respect  to  their  "  brightness  ;  "  and  in  resj)ect  of  brightness,  a 
certain  shade  of  red  may  differ  more  from  another  shade  of  red  than 
it  differs  from  some  shade  of  yellow,  green,  or  blue.  The  bright- 
ness of  a  color  is,  scientifically  speaking,  dependent  both  upon 
the  degree  of  saturation  which  the  color  possesses  and  upon  the 
total  intensity  of  the  light. 

§  5.  A  color-tone  is  said  to  be  "  pure  "  or  "  saturated  "  when  it  is 
free  from  all  admixture  of  other  color-tones.  Pure  or  saturated 
color-tones  can  be  obtained  only  by  use  of  the  spectrum,  which, 
on  account  of  the  different  refrangibility  of  the  different  colored 
rays  that  compose  it,  analyzes  the  compound  ray  of  white  light  into 
its  constituent  color-tones.  By  stimulating  with  different  simple 
rays  those  nervous  elements  which  have  the  same  local  situation 
at,  or  very  near,  the  pole  of  the  eye,  we  test  the  question  whether 
each  special  color-sensation  corresj)onds  to  a  special  physical  con- 
struction of  the  stimulus.  It  is  thus  discovered  that  the  compound 
ray  of  sunlight,  so  far  as  it  stimulates  the  human  eye,  is  made  up 
of  components  formed  by  oscillations  varying  all  the  way  between 
about  three  hundred  and  seventy  billions  and  about  nine  hundred 
billions  per  second  ;  and  that  the  color-tone  of  the  sensation  changes 
as  the  number  of  these  oscillations  changes.  The  following  table ' 
exhibits  these  facts  on  the  scale  of  Fraunhofer's  lines,  which  mark 
those  portions  of  the  spectrum  where  its  principal  colors  appear 
most  obvious  to  the  normal  eye. 

'  Taken  from  Fick,  Physiolog.  Optik,  iu  Hermann's  Handb.  d.  Physiolog., 
Ill,  i.,  p.  173. 


COLOE-TONES   OF   THE   SPECTRUM. 


329 


Name  of  the  line. 

Number  of  vibra- 
tions per  second. 

Wave-length  in  the  air. 

B 

Billions. 
450 
472 
526 
589 
640 
722 
790 

Millimeters. 

0.0006878 

C 

0  0006564 

D 

0.0005888 

E 

0  0005260 

F 

0  0004843 

G 

0.0004291 

H 

0  0003928 

Rays  of  light  which  have  a  number  of  oscillations  less  than  four 
hundred  and  seventy  billions  |Der  second,  so  far  as  they  affect  the 
retina  at  all,  occasion  the  sensation  of  Red  ;  and  this  sensation  does 
not  vary  essentially  in  quality  when  the  oscillations  are  four  hundred 
and  forty  to  four  hundred  and  sixty  billions.  But  when  their  number 
increases  beyond  four  hundred  and  seventy  billions  (C)  the  quahty 
of  the  sensation  changes  rapidly,  takes  on  a  yellow  tone  (Orange- 
yellow),  and  finally,  at  about  five  hundred  and  twenty-six  billions 
(D),  corresponds  to  what  we  definitely  call  Yellow.  This  yellow 
becomes  greenish  as  the  oscillations  increase  in  number,  until  they 
reach  about  five  hundred  and  eighty -nine  billions  (E),  when  Green 
appears.  (Changes  from  yellow  to  green  occupy  only  a  small  zone 
in  the  spectrum.)  The  green  in  turn  becomes  bluish ;  at  six  hun- 
dred and  forty  billions  (F)  Blue  begins  to  appear.  From  this  point 
to  seven  hundi-ed  and  twenty-two  billions  (F-G)  the  color-tones 
that  lie  between  blue  and  violet  are  run  through  ;  beyond  the  latter 
number  Violet  comes  to  view. 

The  color-tones  of  the  spectrum  are,  therefore,  not  sharply  sepa- 
rated, but  pass  gTadually  into  each  other.  The  nearer  together  two 
colors  are  situated  in  the  spectrum,  the  more  nearly  do  they  corre- 
spond in  the  quality  of  their  sensations.  Nor  has  the  spectrum  any 
sharply  defined  limit  at  either  end,  but  passes  gradually  into  black 
— more  gradually  at  the  violet  than  at  the  red  end.  The  energy 
of  the  ultra-red  rays,  as  measured  by  their  physical  and  chemical 
action,  is  greater  than  that  of  the  more  highly  refrangible  rays. 
The  fact  that  these  rays  do  not  excite  visual  sensations  must,  then, 
be  due  to  the  structure  of  the  retina.  The  ul(ra-\iolei  end  of  the 
spectrum  has  been  made  visible  for  a  certain  extent  by  experiment ; ' 
it  produces  the  sensation  of  a  glimmer  of  lavender-gray  color.  Our 
inability  to  perceive  these  ultra-red  and  wZ^ra-violet  rays  is  not  to 
be  considered  an  imperfection  of  the  eye,  as  Tyndall  thought.  It 
is  rather  purposeful,  and  of  the  greatest  importance  for  vision  ; 
since,  if  these  ultra  rays  were  visible,  the  clearness  of  objects  would 
'-  See  Helmholtz,  Physiolog.  Optik,  p.  232  f. 


330  SENSATIONS   OF   SIGHT. 

be  much  disturbed  by  tbe  chromatic  aberration  of  the  refracting 
appai'atus  of  the  eye.' 

§  6.  Besides  the  foregoing  distinctions  of  color-tones,  the  im- 
pression made  by  the  green-yellow  of  the  spectrum  (D-E,  and  im- 
mediately about  D)  is  by  far  the  strongest ;  or,  as  we  should  say, 
this  color  is  naturally  the  "brightest  "  of  the  spectral  colors.  From 
the  region  immediately  around  D,  the  brightness  of  the  color-tones 
diminishes  toward  both  the  red  and  the  violet  ends  of  the  spectrum 
— at  first  quickly,  then  more  slowlj',  and  then  more  quickly  again. 
Such  a  relation  cannot  be  due  to  the  spectrum  as  an  objective 
affair  ;  for  if  we  measure  by  other  physical  means  the  amount  of 
energy  belonging  to  its  different  regions,  we  find  that  of  the  red 
rays  (which  are  by  no  means  brightest)  to  be  strongest.     "We  must. 


Fig.  91. —  (From  Fick.)  The  letters  on  the  horizontal  line  stand  for  Fraunhofer's  lines.  The 
ordinates  of  the  interrupted  curved  line  show  the  brightness  of  rays  as  seen  ;  the  ordinates  of 
the  dark  curved  line,  the  intensity  of  the  rays  as  measured  by  calorific  effect. 

then,  seek  an  explanation  in  the  structure  of  the  retina,  and  conclude 
that  it  is  peculiarly  sensitive  to  stimulations  by  oscillations  of  about 
five  hundred  and  fifty  billions  per  second.  The  sensitiveness  of  the 
retina  to  slight  variations  in  color-tone,  as  dependent  upon  differ- 
ences in  the  wavelengths  of  the  stimulus,  is  also  different  at  different 
portions  of  the  spectrum.  It  is  greatest  in  the  green  and  blue- 
green  regions  (D  and  F). 

The  following  table  represents  both  the  foregoing  laws.  The 
numbers  of  the  second  and  third  columns  show  the  relative  bright- 
ness with  which  the  different  colors  of  the  spectrum  appear  to  the 
eye,  as  calculated  by  different  methods  and  by  two  observers.  It 
will  be  seen  that  the  results  agree  substantially,  though  by  no 
means  perfectly.  In  the  last  two  columns  the  letter  sstand  for 
Fraunhofer's  lines,  and  the  figures  give  the  fractional  variation  in 
the  wave-lengths  which  produces  an  observable  variation  in  the 
color-tone  for  different  regions  of  the  spectrum.'' 

'  See  Fick,  Compendium  d.  Physiologie,  2d  edition,  p.  181  f • ;  and  Her- 
mann's Handb.  d.  Physiol.,  III.,  i.,  p.  181  f. 

■■*  See  Helmholtz's  Physiolog.  Optik,  p.  317  f.;  von  Kries,  in  Archiv  f.  Anat. 
u.  Physiol.,  Physiolog.  Abth.,  1882  (Appendix),  pp.  56-76  ;  Fick,  in  Hermann's 
Handb.  d.  Physiol,  III.,  i.,  p.  174  f. ;  MandelstammandDobrowolsky,  in  Aichiv 
f.  Ophthalmologie,  XIII.,  ii.,  p.  899,  and  XVIII.,  i  ,  p.  66. 


MIXED   COLOE-IMPRESSIONS. 


331 


Fraunhofer. 

Vierordt. 

33 

22 

94 

128 

640 

780 

1,000 

1,000 

480 

870 

170 

128 

31 

8 

5.6 

0.7 

Mandelstamm  and  Dobrowolsky. 


Red,  B 

Orange,  C 

Reddish -yellow,  D 

Yellow,  D-E 

Green.  E 

Blue-green,  F 

Blue.  G   

Violet,  H 


B  .. 

C... 
C-D 
D.. 
D-E 
E  .. 
E-F 
F... 
G... 
H.. 


1  1  5 


id  I 

340 
dl7 


Y7^ 
— L-^ 


-  §  7.  The  colors  of  every-day  experience,  like  its  musical  tones,  are 
not  simple  and  pure  color-tones,  such  as  are  obtained  by  spectral 
analysis  ;  they  are  composite.  Inquiry  must  therefore  be  raised  as 
to  the  effect  produced  in  sensation  from  the  co-working  of  two 
homogeneous  ra^'s  of  light  upon  the  same  elements  of  the  retina 
under  all  the  normal  conditions  to  which  reference  was  previously 
made.  In  pursuing  this  inquiry  no  direct  assistance  can  be  ob- 
tained from  the  discriminations  of  consciousness  ;  for  sensations  of 
color,  unlike  those  of  musical  clang,  cannot  be  mentally  analyzed 
into  their  constituent  elements.  The  science  of  optics  makes  us 
acquainted,  however,  with  the  following  facts  :  When  the  wave- 
lengths of  the  two  colors  mixed  vary  but  slightly  (a  few  billions  of 
oscillations  in  a  second)  from  each  other,  the  color  resulting  from 
the  mixture  lies  between,  and  may  be  recognized  as  a  "  shade  "  of, 
the  colors  mixed.  By  selecting  for  mixture  color-tones  that  lie 
apart  at  all  possible  distances  along  the  spectrum,  an  indefinite 
number  of  impressions  of  color  may  be  obtained,  which  all  differ 
from  those  obtained  by  the  homogeneous  colors.  These  mixed 
color-impreHHions,  however,  are  not  all  different  from  each  other  ; 
so  that  the  number  of  the  qualities  of  resulting  sensations  is  far  less 
than  that  of  the  compound  physical  processes  which  stimulate  the 
retina.  Their  character  depends  both  upon  the  place  of  the  spec- 
trum from  which  the  simple  color-tones  are  selected  for  mixture, 
and  also  upon  the  relative  intensity  of  the  ones  selected.  For  ex- 
ample, if  a  ray  of  four  hundred  and  fifty  billions  of  oscillations  per 
second  (red)  be  mixed  with  one  of  seven  hundred  and  ninety  billions 
(violet),  anew  series  of  impressions  of  color  (the  purples)  is  attained 
by  varying  the  intensities  of  the  two.  These  impressions  are  more 
or  less  like  red  or  like  violet,  according  to  the  relative  amounts  of 
the  rays  of  four  hundred  and  fifty  billions  and  of  seven  hundi-ed  and 
ninety  billions  which  enter  into  the  mixture.  Moreover,  there  are 
found  to  be  two  ways  of  advancing  by  this  process  of  mixing  color* 


332 


SENSATIONS    OF   SIGHT. 


tones  toward  any  one  of  the  composite  colors.  Thus,  we  may  pass 
from  yellow  to  blue  either  through  green-yellow,  green,  and  blue- 
green,  or  through  orange,  red,  purple,  and  violet.  The  following 
table '  is  of  interest  in  this  connection.  Where  two  colors  are  given 
as  resulting  from  the  mixture,  the  variation  is  to  be  understood  as 
dependent  upon  the  prevailing  intensity  of  one  of  the  two  compo- 
nents. 


Components. 


Red  and  Yellow  

Orange  and  Yellow-green 

Yellow  and  Green 

Yellow-green  and  Blue-green . . 

Green  and  Cyanic  Blue 

Blue-green  and  Indigo 

Cyanic  Blue  and  Violet 

Red  and  Yellow-green 

Red  and  Green 

Violet  and  Blue-green 

Violet  and  Green 

Violet  and  Orange 

Red  and  Cyanic  Blue 

Red  and  Indigo 


Tone  of  the  color  obtained  by  mixture. 


Orange 

Yellow 

Yellow-green  

Green 

Blue-green 

Cyanic  Blue 

Indigo 

Orange  or  Yellow    

Orange  or  Yellow  or  Yellow-green. .  .  . 

Indigo  or  Cyanic  Bine 

Indigo  or  Cyanic  Blue  or  Blue-green. 

Red 

Indigo  or  Violet 

Violet 


Degree  of 
saturation. 


Spectral. 

Spectral. 

Whitish. 

Very  whitish. 

Whitish. 

Spectral. 

Spectrid. 

Spectral. 

Whitish. 

Spectral. 

Whitish. 

Whitish. 

Whitish. 

Slightly  whitish. 


§  8.  The  number  of  colors  distinguishable  by  the  human  eye  is 
not  easily  stated  with  accuracy  ;  like  the  number  of  musical  tones, 
it  varies  with  different  individuals.  The  usual  number  of  seven 
fundamental  colors,  as  fixed  by  Newton,  with  the  intent  of  forming 
an  octave  in  the  scale  of  color-tones,  has  no  sufficient  claim  to 
acceptance.  Six  of  the  seven — namely,  red,  orange,  yellow,  green, 
blue,  violet — are  indeed  names  in  common  use.  But  indigo,  as  an 
intermediate  tone,  or  kind  of  semitone,  between  blue  and  violet, 
has  perhaps  no  more  real  right  to  recognition  than  various  other 
intermediate  color-tones.  Bonders "  puts  the  number  of  color-tones 
distinguishable  in  oil-colors  at  one  hundred  ;  von  Kries  '  the  rec- 
oo-nizable  number  of  spectral  tints  at  about  two  hundred  and 
thirt}'.  But  each  of  these  yields  different  sensations  of  color  ac- 
cording to  the  degree  of  its  saturation  or  purity,  due  to  freedom 
from  admixture  of  white  light.  Another  series  of  variations  of  sen- 
sation must  be  allowed  for,  which  are  due  to  differences  in  "  bright- 
ness "  or  intensity.  Introducing  these  two  variable  elements,  von 
Kries  calculates  the  number  of  distinctions  of  color-sensations, 
possible  for  all  degrees  of  purity  of  tone  and  intensity  of  light,  at 

'  Made  according  to  investigations  by  J.  J.  Miiller,  and  taken  from  Tick,  in 
Hermann's  Handb.  d.  Physiol.,  III.,  i.,  p.  190. 
'^  Archiv  f.  Ophtbalmologie,  XXVII. 
2  Arcbiv  f.  Auat.  u.  Physiol.,  Physiolog.  Abth.,  1882  (Appendix),  p.  58  f. 


THE   COMPLEMENTARY   COLORS. 


333 


about  five  hundred  thousand  to  six  hundred  thousand.  This  num- 
ber stands  midway  between  the  "  many  milHons  "  of  which  Au- 
bert  speaks  and  the  five  thousand  allowed  by  Douders.  Herschel 
thought  that  the  workers  on  the  mosaics  of  the  Vatican  must  have 
distinguished  at  least  thirty  thousand  different  colors. 

§  9.  Experiment  also  shows  that  if  certain  color-tones  with  a 
given  intensity  are  united  on  the  retina,  the  result  is  a  sensation 
unlike  that  of  any  other  of  the  colors,  whether  pure  or  mixed. 
This  sensation  we  call  "white,"  and  the  two  colors  which  by  their 
admixture  produce  it  are  called  "  complementary."  Complementary 
colors  may  be  mixed  upon  the  retina  in  various  ways  ;  either  by  al- 
lowing two  spectral  rays  properly  selected  to  be  superimposed  at 
the  same  spot,  or  by  blending  the  reflected  images  of  two  colored 
wafers,  or  by  blending  the  du'ect  visual  impressions  of  colored 
surfaces  on  a  swiftly  revolving  top  or  wheel,  etc.  But  however 
mixed,  the  resultant  sensation  is  that  of  a  so-called  "  white  "  color 
in  which  all  trace  of  the  constituent  elements  is  lost.  Following  is 
a  table  of  complementary  colors  : ' 


Color. 

Wave-len^h. 

Complementary 
color. 

Wave-length. 

Relation  of 
wave-lengths. 

Red 

2,425 
2,244 
2,162 
2,120 
2,095 
2,085 
2,082 

Green-blue  . . . 
Blue 

1,818 
1,809 
1,793 
1,781 
1,716 
1,706 
1,600  {^i 

1,384 

Orange  

1,240 
1,206 

Gold-yellow  .. . 
Gold-yellow. . . 

Yellow 

Yellow 

Green-yellow. . 

Blue 

Blue 

1,190 

Indigo  blue. . . 
Indigo-blue. .  . 
Violet 

1,221 
1,222 
1,301 

§  10.  If  the  foregoing  facts  and  laws  are  held  to  be  true  of  the 
"  normal "  connection  between  light  and  visual  sensations,  then 
various  classes  of  circumstances  must  be  taken  account  of  as  "ab- 
normal," which,  nevertheless,  enter  into  all  our  daily  experience 
with  this  sense.  Indeed,  the  connection  between  stimulus  and 
sensation  is  not  the  same  for  different  individuals  who  possess  sub- 
stantially the  same  color-sensations  ;  frequently  the  complementary 
colors  for  two  different  indi%T.duals  are  not  precisely  the  same. 
Even  the  two  eyes  of  the  same  individual  often  differ  percejDtibly 
in  this  regard.  Important  changes  in  the  quality  of  the  sensations, 
other  than  those  directly  ascribable  to  changes  in  the  wave-lengths 
of  Hght,  take  place  when  the  intensity  of  the  light  approaches  ei- 

'  Taken  from  Helmlioltz,  Pliysiolog.  Optik,  p.  277.  The  numbers  are  given 
in  hundred  milliontlis  of  a  Parisian  inch,  and  may  be  reduced  to  millimetres 
by  multiplying  by  27.07. 


334  SENSATIONS    OF   SIGHT. 

tliei-  a  masimum  or  a  minimum.  At  the  maximum  intensities  of 
the  stimulus  all  sensations  of  color-tone  cease,  and  even  homoge- 
neous rays  appear  white.  Previous  to  reaching  this  maximum, 
red  and  green  pass  over  into  yellow.  At  the  mininium  intensities 
of  light  every  color-tone  except  the  pure  red  of  spectral  saturation 
appears  colorless  when  seen  alone  on  a  perfectly  black  ground. 
The  different  colors  appear  and  disajjpear,  as  such,  at  different 
degrees  of  intensity  of  the  stimulus — green,  among  them  all,  re- 
maining visible  in  the  weakest  light.  They  all  also  change  their 
tone  as  the  light  which  falls  on  them  diminishes  ;  but  it  is  scarcely 
possible  to  describe  the  law  of  this  change,  on  account  of  the  great 
difficulty  of  distinguishing  color- tones  in  very  weak  light. 

§  11.  Changes  of  color  also  take  place  when  the  time  of  the 
action  of  the  light  is  reduced  to  a  minimum.  Sensations  of  satu- 
rated color  can  be  produced  by  instantaneous  illumination  of  the 
spectrum  with  the  electrical  spark.  More  time  is  needed,  however, 
to  produce  these  sensations  with  smaller  intensities  of  the  light. 
The  different  colors,  even  when  of  the  same  brightness,  appear  to  re- 
quire different  amounts  of  time  in  order  to  reach  the  maximum  of 
their  effect— red,  0.0573;  blue,  0.0913  ;  green,  0.133  of  a  second.' 
The  tone  of  the  color  varies  with  the  duration  of  the  impression  as 
well  as  with  the  intensity  of  the  Hght.  Very  minute  objects,  too, 
appear  of  a  different  color  on  account  of  their  size.  In  general,  the 
larger  the  surface,  the  less  the  intensity  of  the  light  necessary  to 
produce  the  sensation  of  any  particular  color-tone  ;  the  greater  the 
intensity  of  the  light,  the  smaller  the  surface  which  will  suffice  for  . 
such  sensation.  Fick ''  has  shown  that  the  color-sensations  derived 
from  small  dislinct  points  support  each  other,  as  it  were,  in  the 
same  way  as  the  contiguous  points  of  a  colored  surface.  For  if  we 
make  with  a  fine  needle  a  single  hole  (of  about  0.6  mm.  in  diameter) 
in  a  sheet  of  paper  and  look  through  it  at  colored  paper  distant 
some  six  and  a  half  metres,  the  color  of  the  paper  cannot  be  dis- 
ting-uished.  But  if  the  number  of  holes  be  as  many  as  sixteen, 
the  color  can  be  distinguished  at  the  same  distance,  even  when  the 
holes  through  which  we  look  are  smaller.  Subsequent  experiment^ 
has  shown  that  the  smaller  the  distance  between  the  single  perfo- 
rations, the  greater  the  distance  at  which  the  eye  can  recognize 
colors  through  them.  In  general,  then,  two  weak  sensations,  each 
of  which  belongs  to  one  eye,  may  fuse  together  into  one  strong 
one. 

'  According  to  Kunkel,  in  Pfluger's  Archiv,  ix. ,  p.  207. 

*  Pfluger's  Archiv,  xvii.,  p.  152. 

*  See  Dobrowolsky,  in  Pfluger's  Archiv,  xxxv.,  p.  536 f. 


KINDS   OF   COLOR-BLIlSrDISrESS.  335 

§  12.  Very  important  changes  in  the  visual  sensations  occur  as 
dependent  on  the  place  of  the  retina  which  is  stimulated.  In  this 
respect  a  great  difference  exists  between  the  central  and  the  pe- 
ripheral parts.  The  entire  field  of  this  organ  may  be  somewhat 
indefinitely  divided  into  three  zones — a  central  or  polar,  a  middle, 
and  an  outer  or  peripheral.  It  is  probably  true  that  the  periph- 
eral parts  of  the  retina  produce  no  sensations  which  cannot  be 
produced  by  stimulating  the  central  zone.'  But  it  is  equally  true 
that,  under  the  same  circumstances,  the  same  stimulus  produces 
a  markedly  different  effect  upon  sensation  when  applied  to  differ- 
ent localities  of  the  retina.  Rays  which,  falling  on  the  polar  zone, 
produce  the  impression  of  red,  yellow,  or  green,  all  make  an  im- 
pression of  yellow  when  they  fall  on  the  surrounding  zone  (a  few 
millimetres  from  the  fovea  centralis)  ;  and  this  yellow  is  so  much 
the  paler,  the  greener  the  impression  on  the  polar  zone.  Rays 
which  make  on  the  polar  zone  the  impression  of  blue  or  violet  make 
on  the  outer  zone  the  impression  of  blue ;  and  this  blue  is  so 
much  the  paler,  the  nearer  the  imi:)ression  on  the  polar  zone  is  to 
green.  It  follows,  then,  that  whereas  thei'e  is  at  the  central  zone 
an  indefinite  number  of  color-tones  possible,  this  number  is  re- 
duced to  comparatively  few  impressions  at  the  middle  zone  ;  while 
all  color-tones  gradually  become  indistinguishable  and  are  lost  on 
passing  through  the  outer  zone.  These  great  changes  in  sensi- 
tiveness to  color  are  not  accompanied  by  similar  changes  iii  sen- 
sitiveness to  colorless  light ;  it  even  appears  that  regions  of  the 
retina  distant  about  30°  from  its  centre  are  more  sensitive  to  light 
than  is  the  polar  zone. 

A  certain  proportion  of  persons  (perhaps  one-twentieth  or  more) 
appear  to  have  a  defective  structure  of  the  retina,  which  may  be 
described  as  corresponding  in  the  polar  zone  to  that  of  the  normal 
retina  in  the  middle  or  even  the  outer  zone.  Such  persons  are  said 
to  be  "color-blind."  The  farther  outward  this  imperfect  condition 
of  the  retina  extends,  the  nearer  does  the  defect  approach  to  total 
color-blindness.''  In  most  cases  of  this  defect  there  is  a  partial  or 
complete  insensitiveness  to  the  red  rays ;  these  rays  are  especially 
liable  to  be  confused  with  the  dark-green  or  the  yellow.  The  spec- 
trum is  thus  shortened  at  the  red  end.  Cases  of  so-called  violet- 
blindness,  as  reported  by  Donders  and  Stilling,  are  much  more  rare 
and  doubtful.     In  total  color-blindness  only  shades  of  gray  from 

'  See  von  Kries,  Archiv  f.  Anat.  ix.  Physiol.,  Physiolog.  Abth.,  1883  (Ap- 
pendix), p.  90. 

'^  See  Fick,  Zur  Tlieorie  d.  Farbenblindbeit,  p.  213  f.  ;  and  in  Hermann's 
Handb.  d.  Phyfaiol.,  III.,  i.,  p.  206  f. 


336  SENSATioisrs  of  sight. 

white  to  black  are  visible.  In  general,  the  attempts  to  make  out  a 
spectrum  for  the  color-blind  are  unsatisfactory,  since  we  can  only 
be  sure  as  to  what  color-tones  appear  like  or  unlike  to  them  ;  we 
cannot,  on  the  contrary,  be  sure  that  their  abnormal  sensations  are 
like  any  of  our  normal  sensations — in  other  words,  that  what  they  see 
when  red  light  falls  on  the  retina  corresponds  to  any  of  our  color- 
tones.  The  three  or  four  cases  reported  where  one  eye  of  a  person 
has  been  normal  and  the  other  color-blind  are,  of  course,  especially 
valuable  ;  since  they  offer  an  opportunity  to  compare  immediately 
the  sensations  of  the  normal  with  those  of  the  pathological  eye. 
These  cases,  according  to  von  Kries '  show  that  the  two  funda- 
mental colors  to  which  the  color-blind  are  reduced  may  be  con- 
sidered as  either  red  and  blue-green  or  greenish-yellow  and  blue- 
violet. 

§  13.  Important  modifications  of  the  normal  action  of  the  eye  are 
also  caused  by  the  previous  coj^cZiiion  of  the  retina,  or  by  the  contem- 
poraneous condition  of  parts  of  it  contiguous  to  those  on  which  the 
light  falls.  The  former  fact  explains  the  phenomena  of  "  inertia  " 
and  "  exhaustion  ;  "  the  latter,  the  phenomena  of  "  contrast."  The 
reaction  of  the  sense  of  sight  is  relatively  very  sluggish  ;  or — in 
other  words — the  inertia  of  the  eye  is  relatively  great.  This  fact 
is  undoubtedly  due  to  the  chemical  nature  of  the  stimulus  which 
acts  directly  upon  its  end-organs.  The  light  requires  time  in  order 
to  effect  those  photo-chemical  changes  on  whose  action  upon  the 
nervous  elements  of  the  retina  our  sensations  of  light  and  color 
depend.  On  the  other  hand,  if  we  close  the  eyes  after  looking 
intently  upon  any  bright  object,  the  image  of  this  object  remains 
for  some  time,  and  only  slowly  fades  out  of  sight.  Such  an  image 
is  called  a  "positive  after-image,"  because  its  bright  and  dark  lines 
and  surfaces  correspond  to  those  of  the  original  object.  The  delay 
which  the  sensations  undergo,  both  in  forming  and  in  fading  away, 
is  said  to  be  due  to  the  inertia  of  the  retinal  structure.  It  is,  of 
course,  a  law  of  all  nervous  excitation  and  action  that  it  requires  a 
certain  amount  of  time  for  beginning  and  for  changing  its  char- 
acter. 

White  positive  after-images  (as  Fechner,  Helmholtz,  and  oth- 
ers have  shown)  pass  quickly  through  greenish-blue  to  indigo- 
blue  and  then  to  violet  or  rose-color.  But  "negative  after-images  " 
are  due  to  the  exhaustion  of  the  retina.  If  the  eye  be  intently 
fixed  for  some  time  on  a  small  square  of  black  lying  upon  a  sheet 
of  white  paper,  and  then  suddenly  turned  upon  the  white  surface, 
a  bright  square  appears,  moves  about  with  the  eye,  and  slowly 
'  ArcLiv  f.  Anat.  ij..  Physiol.,  Physiolog.  Abth.,  1883  (Appendix),  p.  153  £ 


PHENOMElSrA   OF   CONTRAST.  337 

fades  away.  If  wg  look  for  a  long  time  at  a  green  surface  and  then 
direct  the  eye  upon'a  white  one,  the  latter  appears  for  a  moment  to 
be  of  a  red  color.  In  general,  the  color  of  the  negative  after-image 
is  such  that,  when  combined  with  the  color  of  the  object,  the  two  will 
produce  white.  In  other  words,  the  color  of  such  an  image  is  "  com- 
plementary "  of  the  color  of  the  object.  Such  facts  as  the  foregoing 
must  in  some  manner  be  brought  under  the  law  which  applies  to  all 
the  elements  of  the  nervous  system,  but  especially  to  the  end-organs 
and  the  central  organs  ;  these  organs  become  wearied  by  continuous 
use,  and  require  time  for  recovery  of  their  suspended  or  diminished 
functions.  Precisely  how  the  application  is  to  be  made  lo  the  case 
of  the  retina  is,  however,  a  matter  of  the  general  physiological  the- 
ory of  vision  which  cannot  as  yet  be  stated  with  perfect  certainty. 
The  phenomena  of  exhaustion  are  among  the  most  important  for 
the  formation  of  such  a  theory.  Investigations  in  this  direction 
have  led  to  the  discovery  that  none  even  of  the  spectral  colors  are 
perfectly  saturated,  since  each  of  them  can  be  made  to  appear  more 
so  by  looking  at  it  with  an  eye  wearied  by  the  complementary 
color. '  Red  is  most  nearly  saturated,  blue  and  yellow  next,  and 
green  least  of  all. 

§  14.  The  different  ]3arts  of  the  retina  are  interdependent  in  the 
production  of  sensation  ;  or — to  employ  the  statement  of  Wundt  ^ 
— "  The  sensation  which  arises  through  the  stimulation  of  any  given 
point  of  the  retina  is  also  a  function  of  the  state  of  other  immedi- 
ately contiguous  points."  Hence  arise,  in  part  at  least,  the  phe- 
nomena of  contrast,  which  are  of  two  kiiads — contrast  of  bright- 
ness and  contrast  of  color-tone.  The  fundamental  fact  in  the  first 
class  of  contrasts  is  this  :  every  bright  object  appears  brighter  with 
surroundings  darker  than  itself,  and  darker  with  surroundings 
brighter  than  itself.  These  phenomena  are  explained  by  Helm- 
holtz  ^  as  deceptions  of  judgment,  such  as  we  are  accustomed  to  in 
our  estimates  of  distances.  To  this  explanation,  however,  Fick,* 
Hering,^  and  others  oppose  strong  and  apparently  conclusive  ob- 
jections. They  would  explain  the  same  phenomena  by  the  modify- 
ing influence  of  the  excitation  of  one  part  of  the  retina  upon  the 
excitation  of  contiguous  parts.     Such  influence  does  not  always 

^  Comp.  Helmlioltz,  Physiolog.  Optik,  p.  279  f.  ;  Exner,  in  Pfliiger's  Archiv, 
i.,  p.  389;  and  see,  especially,  von  Kries,  Archiv  f.  Auat.  u.  Physiol.,  Phy- 
siolog. Abth.,  1882  (Appendix),  p.  115. 

-  Physiolog.  Psychologie,  i.,  p.  439. 

3  Physiolog.  Optik,  pp.  388  ff. 

*  In  Hermann's  Handb.  d   Physiol.,  III.,  i.,  p.  231  f. 

^  Sitzgsber.  d   Wiener  Acad,  June,  1872,  and  December,  1873. 
22 


338  SENSATIONS    OF    SIGHT. 

take  the  form  of  depressing  the  excitabihty  of  the  contiguous 
parts  ;  on  the  contrary,  stimulating  certain  elements  for  some  time 
may  finally  involve  contiguous  ones  in  a  secondary  way.  This  fact 
they  consider  to  be  the  true  explanation  of  the  spreading  of  a 
bright  object  on  a  dark  background,  whose  after-image  becomes  a 
clear  band  of  light  around  the  dark  image  of  the  bright  object. 
When  colored  instead  of  white  light  is  used  in  experimenting  under 
the  law  of  conti'ast,  phenomena  similar  to  those  of  complementary 
colors  are  obtained.'  A  small  square  of  white  on  a  surface  of  green, 
when  covered  with  a  transparent  sheet  of  tissue-paper,  appears  as 
red  on  a  surrounding  surface  of  a  whitish  hue  ;  on  a  red  ground  it 
appears  as  green,  on  a  blue  ground  as  yellow,  and  vice  ver'sa.  There 
is  the  same  dispute  over  these  as  over  the  other  phenomena  of 
contrast.  Shall  they  be  considered  as  cases  of  deception  of  judg- 
ment, or  do  they  admit  of  a  physiological  explanation  ?  Mere 
cases  of  deception  they  cannot  well  be.  The  theory  which  ascribes 
to  each  part  of  the  retina  an  influence  upon  other  contiguous  parts 
is  the  most  satisfactory  form  of  a  physiological  explanation.  But 
such  physiological  explanation  seems  to  need  supplementing  by 
reference  to  induced  conditions  of  the  central  organs,  concei'ning 
the  nature  of  which  we  ai'e  thus  far  almost  entirely  ignoi'ant. 

§  15.  It  will  readily  be  seen  that  a  theory  which  shall  satisfac- 
torily account  for  the  complicated  phenomena  of  visual  sensations 
is  difficult  to  establish.  Physiological  optics  will  probably  never 
be  able  to  explain  in  detail  the  individual  sensations  of  light  and 
color.  But  each  claimant  to  present  such  theory  must,  as  Wundt ' 
maintains,  account  for  the  following-  four  main  classes  of  facts  :  (1) 
The  subjective  i-elations  of  the  color-tones,  and  the  fact  that  they 
may  all  be  graded  downward,  as  it  were,  into  colorless  light ;  (2) 
the  law  of  the  mixing  of  all  the  colors  from  three  (or  more)  funda- 
mental color-tones  ;  (3)  the  phenomena  of  after-images  ;  and  (4) 
the  phenomena  of  contrast.  Among  all  the  hypotheses  hitherto 
proposed  to  account  for  the  quality  of  visual  sensations,  that  brought 
forward  by  Young,  and  elaborated  and  applied  b}'  Helmholtz,  is  by 
far  the  most  prominent.  This  hypothesis  takes  its  point  of  start- 
in<T  from  the  undoubted  fact  that,  by  admixture  of  a  few  so-called 
fundamental  color-tones,  we  can  produce  all  the  other  colors,  as 
well  as  the  sensation  called  "white."  There  are  said  to  be /Aree 
such  color-tones,  because  this  is  the  smallest  number  which  will 
account  for  the  facts.  Of  these  three,  green  must  be  one,  since,  in 
the  spectrum  of  colors,  this  tone  has  no  complementary  color.    Green 

'  See  Helmlioltz,  Physiolog,  Optik,  pp.  388  E. 
^  Physiolog.  Psycliologie,  i  ,  p.  450. 


THE   YOUT^G-HELMHOLTZ  THEOEY. 


339 


being  fixed,  the  other  two  color-tones  must  be  chosen  from  near  the 
ends  of  the  spectrum,  and  in  such  a  way  that,  when  combined  with 
spectral  green,  they  will  produce  white.  Ked  (carmine-red,  ac- 
cording to  Fick)  and  either  violet  (so  Young  and  Helmholtz)  or  blue 
(indigo-blue,  Fick)  best  fulfil  the  required  conditions.  It  is,  then, 
assumed,  by  the  Young-Helmholtz  theory,  that  in  every  portion 
of  the  retina  which  is  susceptible  to  color  there  exist  three  kinds 
of  nervous  elements,  the  excitation  of  which  separately  would  pro- 
duce three  distinct  kinds  of  sensations  ;  and  that  each  kind  of  ele- 
ment is  capable  of  producing  only  that  kind  of  sensation  which  is 
peculiar  to  itself.  It  apparently  follows  that  each  of  these  three 
kinds  of  nervous  elements  has  its  special  form  of  end-apparatus,  the 
excitability  of  which  differs  from  that  of  the  others  ;  that  is  to  say, 


Fig.  92. — Diagram  from  Fick,  illustrating  the  Young-Helmholtz  Theory.     (For  explanation,  see 

the  text. ) 

there  are  fibres  of  red  color-sensation,  whose  end-apparatus  responds 
specifically  to  rays  of  small  refrangibility  ;  fibres  of  green  color- 
sensation,  whose  end-appai*atus  responds  to  rays  of  medium  re- 
frangibility :  and  fibres  of  violet  or  blue  color-sensations,  whose 
end-apparatus  responds  to  rays  of  great  refrangibility.  We  must 
suppose,  however,  since  we  cannot  directly  analyze  into  their  com- 
ponents the  sensations  which  appear  in  consciousness,  that  no  one 
of  the  three  kinds  of  elements  is  ordinarily  excited  alone.  Every 
actual  sensation  of  color  is  therefore  a  complex  affair,  whose  char- 
acter is  determined  by  the  relations  in  which  each  one  of  the  three 
intensities  of  excitation  stands  to  both  the  others.  In  explanation 
of  this  assumption  the  following  diagram  is  proposed.'  (See  Fig. 
92.)     The  curved  lines  E,  G,  and  B  represent  the  three  kinds  of 

'  Taken  from  Fick's   Physiolog.  Optik,  in  Hermann  s  Handb.  d.  Physiol., 
III.,  i.,  p.  198;  comp.  Helmholtz,  Physiolog.  Optik^  p.  291. 


340  SENSATIONS   OF   SIGHT. 

nerves  sensitive  to  the  three  fundamental  color-tones — K  to  red,  G  to 
green,  B  to  blue  (indigo).  The  curves  described  by  them  show  the 
strength  of  the  excitation  exercised  by  the  stimulus,  corresponding 
to  the  colors  of  the  spectrum,  upon  each  kind  of  nerves.  The  per- 
pendicular lines  indicate  the  colors  of  the  spectrum  ;  and  the  waj 
these  lines  cut  the  curves  shows  the  relative  strength  of  the  excita- 
tion of  each  kind  of  nerves  w^hich  is  combined  to  produce  these 
colors. 

It  should  be  gratefully  acknowledged  that  the  Young-Helmholtz 
theory  affords  a  brilliant  explanation  of  a  great  many  of  the  phe- 
nomena of  sensations  of  light  and  color.  It  is  most  successful  with 
those  that  relate  to  the  mixijig  of  colors  and  to  complementary 
color.  The  hypothesis  cannot  be  said,  however,  to  be  wholly  ade- 
quate and  satisfactory.  One  of  its  most  intelligent  advocates  (Fick) 
admits  that  it  cannot  explain  the  following  cardinal  fact :  Every 
ray  of  light  which,  so  long  as  it  is  confined  to  a  moderate  extent  of 
the  polar  zone,  makes  the  impression  of  a  saturated  color  produces 
a  whitish  impression,  almost  devoid  of  color-tone,  as  soon  as  it  is 
limited  to  an  extremely  minute  portion  of  the  retina.  This  is  the 
very  opposite  of  what  the  hj'pothesis  would  lead  us  to  expect ;  for, 
according  to  it,  extremely  minute  impressions  on  the  retina  ought 
to  isolate  the  particular  kind  of  fibres,  and  so  yield  tlie  purest 
possible  color-tone.  The  facts  of  histology  seem  rather  adverse 
than  favorable  to  the  theory,  although  not  much  stress  can  be  laid 
upon  them  alone.  Moreover,  it  does  not  satisfactorily  explain  the 
facts  of  contrast  of  colors  and  of  color-blindness.  The  most  re- 
cent investigations  seem  to  indicate  that  cases  of  color-blindness 
cannot  be  accounted  for  by  dropping  out  one  fundamental  kind  of 
nerve-fibres,  as  the  Young-Helmholtz  theory  supposes.'  Various 
other  important  objections  are  raised  by  its  opponents  (especially 
by  Hering,  Wundt,  and  others). 

§  16.  In  order  to  supply  the  alleged  defects  of  the  Young-Helm- 
holtz theory  of  color- sensations,  several  other  theories  have  been 
devised — notably  those  of  Hering  and  of  Wundt.  The  former* 
differs  from  most  other  investigators  in  his  view  of  the  nature  of 
the  changes  of  sensation  which  take  place  as  we,  in  experience, 
run  through  all  the  different  shades  of  gray  from  white  to  black. 
All  such  changes  Hering  considers  analogous  to  those  alterations 
in  the  quality  of  our  sensations  that  would  be  produced  by  jpassing 

'  See  von  Kries,  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth.,  1882  (Ap- 
pendix), pp.  1 84-153. 

^  B.  Hering,  Zur  Lehre  vom  Lichtsinne,  Sitzgsber.  d.  Wiener  Acad.,  6 papers, 
1872-74. 


wutstdt's  theoey  of  coloes.  341 

the  eye  over  a  surface  on  which  the  different  color-tones  almost 
insensibly  shaded  into  each  other.  Hering,  therefore,  proposes  six 
(or  three  pairs  instead  of  three  single  ones)  fundamental  color- 
tones — namely,  black  and  white,  green  and  red,  blue  and  yellow. 
The  changes  which  give  rise  to  sensations  of  black,  green,  and  blue 
are  ascribed  to  the  process  of  "construction  "  of  a  so-called  visual 
substance  ;  those  which  give  rise  to  white,  red,  and  yellow  are  as- 
scribed  to  the  "destruction"  of  such  visual  substance.  The  three 
pairs  of  color-tones  are  thus  made  antagonistic  rather  than  com- 
plementary. But  the  hypothesis  of  Hering  appears  to  involve  more 
uncertain  assumptions,  and  to  explain  fewer  facts,  than  the  one  it 
would  displace.  Moreover,  the  assumption  that  white,  and  its  shades 
down  to  black,  may  be  considered  as  color-tones,  instead  of  altera- 
tions in  the  brightness  of  the  true  color-tones,  is  generally  denied. 

The  theory  of  Wundt '  emphasizes  the  difference  in  processes 
rather  than  in  the  kinds  of  retinal  elements.  It  involves  the  fol- 
lowing principles  :  (1)  In  every  excitation  of  the  retina  two  dif- 
ferent processes  are  set  up,  the  variations  of  which  follow  differ- 
ent laws  ;  one  of  these  is  a  "  chromatic  "  process  (which  gives  us 
color-tones),  and  is  a  function  of  the  length  of  the  waves  of  light ; 
the  other  is  "achromatic,"  and  is  also  dependent  upon  the  wave- 
lengths, but  varies  only  in  intensity  and  remains  in  character  the 
same.  (2)  The  achromatic  excitation  consists  in  a  "uniform  pho- 
to-chemical process,"  which  reaches  its  maximum  at  yellow  and 
falls  off  toward  both  ends  of  the  spectrum.  (3)  The  chromatic 
excitation  is  a  "polyforra  photo-chemical  pi'ocess,"  which  changes 
continuously  with  the  wave-lengths  of  light.  The  extreme  differ- 
ences of  this  length  are  such  as  to  produce  effects  that  approximate 
each  other  ;  while  the  effects  of  certain  different  intervening  wave- 
lengths are  related  in  such  a  way  that  opposed  phases  of  one  and 
the  same  movement  equalize  each  other  perfectly.  (4)  Evei'y  pro- 
cess of  excitation  of  the  retina  outlasts  the  stimulation  for  a  certain 
time,  and  exhausts  the  sensibility  of  the  nerve-substance  for  that 
particular  form  of  stimulation.  The  positive  after-images  are  to  be 
explained  by  the  persistence  of  the  retinal  excitation,  the  negative 
by  exhaustion.  (5)  The  difficult  phenomena  of  contrast  are  to  be 
explained  by  the  general  principle  that  all  impressions  of  light  and 
color  are  experienced  in  relation  to  each  other.  In  other  words, 
they  fall  under  the  general  law  of  relativity. 

§  17.  Von  Kries''  has  subjected  all  the  principal  theories  of  color- 

'  See  Physiolog.  Psychologie,  i. ,  pp.  450  if. 

-  See  Arcliiv  f.   Anat.  u.  Physiol.,  Physiolog.  Abth.,  1883,  Appendix,  pp. 
1-178. 


342 


SENSATIONS   or   SIGHT. 


sensations  to  a  most  searching  criticism  as  considered  in  the  light 
of  all  the  facts.  He  naturally  finds  serious  defects  in  them  all,  but 
arrives  at  the  following  highly  important  conclusions.  The  photo- 
chemical facts  concerned  in  vision  compel  us  to  adopt  a  theory  of 
component  elements  rather  than  one  of  changes  qualitatively  alike 
and  arranged  in  a  continuous  series.  This  would  seem  decisive 
against  the  theory  of  Wundt,  Only  by  the  aid  of  assuming  the 
varied  combination  of  such  elements  can  we  explain  the  phenomena 


sm 


W 


^%^ 


PURPLE 


^XG 


Fig.  93. — Color-Triangle,  from  Fick.     (For  explanation  see  text.) 

of  exhaustion.  Three  series  of  components  are  apparently  requisite : 
one  for  the  bright  and  dark,  but  colorless,  sensations,  and  two 
color-tone  series — a  red-green  series,  and  a  yellow-blue  series. 
White  is,  nevertheless,  not  to  be  considered  as  belonging  to  the 
three,  since  it  corresponds  to  all  the  color-tones  whenever  they 
reach  a  minimum  of  saturation.  The  processes  corresponding  to 
these  three  series  of  components  ma}'  be  located  at  dilferent  places 
in  the  nervous  apparatus  of  vision — either  more  centrally  or  more 


SYMBOLISM   OF   COLOE-TOTs^ES.  343 

peripherally.  The  articulation  and  adjustment,  as  it  were,  of  the 
three  processes  von  Kries  would  assign  to  the  central  organs.  And 
here  we  reach  the  extreme  limits,  not  only  of  our  assured  knowl- 
edge, but  also  of  our  power  to  frame  a  plausible  theory  ;  for  it  ap- 
pears that  all  theories  must  either  leave  certain  important  facts  un- 
explained, or  else  make  further  assumptions  concerning  nervous 
processes — especially  in  the  central  organs  of  vision — of  the  exist- 
ence and  influence  of  which  upon  the  sensations  there  can  be  no 
doubt,  but  of  the  precise  natui-e  of  which  we  are  completely  ig- 
norant. 

§  18.  Much  ingenuity  and  painstaking  have  been  expended  in  de- 
vising some  form  of  si/inbolism  which  should  represent  to  the  ej'ein 
geometrical  relations  the  laws  of  the  sensations  of  light  and  color. 
Obviousl}'  the  sensations  of  this  sense  cannot,  like  those  of  hearing, 
be  symbolized  by  the  relations  of  points  along  a  straight  line. 
Color-tones,  unlike  musical  tones,  form  a  series  of  qualitatively  differ- 
ent sensations  that,  at  certain  places  in  the  scale,  separate  from  each 
other  with  varying  degrees  of  rapidity,  and  then  toward  the  broken 
ends,  as  it  were,  of  this  scale,  tend  to  approach  each  other  again. 
Such  relations  are  most  successfully  set  forth  by  a  triangle,  which 
maybe  constructed  as  in  the  foregoing  figure  '  (93).  In  this  triangle 
the  different  color-tones  may  be  regarded  as  tying  together  along 
the  cuiwed  line,  from  red  to  violet,  and  the  difference  in  any  two 
color- tones  as  measiu'ed  by  the  angle  which  two  lines  make  when 
drawn  from  the  point  W  through  the 
points  occupied  on  the  curve  by  the 
two  color-tones.  For  example,  the 
difference  between  red  and  violet  is 
less  than  that  between  red  and  green, 
as  is  indicated  by  the  fact  tbat  the 
angle  B  TF//is  smaller  than  the  an- 
gle EWG. 

By  Fig.  94  "  the  relations  of  the 
color-tones  as  contrasting  with,  and 
complementary  of,  each  other  are  rep- 

l-esented.         Of     the     two     concentric  Fig.  94.— scheme  for  showing  the  Rela- 

circles,  each  color  in  one  corresponds  *^°'''  °^  Coior-tone  (see  text). 

to  the  complementary  color  of  the  other.  If  the  color  inducing 
the  contrast  is  represented  by  a  segment  of  the  inner  circle,  the 
coincident  segments  of  the  two  circles  represent  the  direction  in 
which  the  induced  change  is  moA-ing,  as  it  were.     For  example, 

'  Taken  from  Fick,  in  Hermann's  Ilandb.  d.  Plij'siol.,  III.,  i.,  p.  184. 
■•^  Taken  from  Wundt,  Physiolog.  Psycliologie,  i.,  p.  442. 


344  SENSATIONS   OF   THE   SKIN. 

since  the  segment  green  coincides  with  purple,  and  red  coincides 
with  blue-green,  green  on  a  red  ground  is  modified  as  it  would  be 
if  blue-green  were  mixed  with  it  ;  and  red,  as  it  would  be  if  purple 
were  mixed  with  it. 

§  19.  At  least  two  specifically  different  forms  of  sensation — namely, 
Pressure  and  Temperature — have  generally  been  admitted  to  have 
their  organ  in  the  skin. '  The  claims  of  various  other  kindred  forms 
of  feeling  to  be  considered  as  primitive  factors  of  our  sense-percep- 
tions, arising  from  the  activity  of  the  skin  as  an  end-organ  of  sense, 
are  more  doubtful.  Sensations  of  motion,  of  innervation  and  weari- 
ness of  the  muscles,  the  so-called  "  common  sensations  "  (or  sensa- 
tions of  the  sensus  communis),  the  sensations  of  pain  or  pleasure,  and 
those  delicate  shadings  of  sensation,  as  it  were,  which  constitute 
the  "  local  coloring  "  of  all  the  feelings  to  which  we  assign  a  definite 
place  in  the  fields  of  sight  and  touch,  are  all  closely  allied  to  sensa- 
tions of  pressure  and  temperature.  But  some  of  these  forms  of 
feeling — as,  for  example,  the  so-called  sensations  of  motion  and  of  the 
sensus  communis— oxe  undoubtedly  complex  modifications  of  certain 
simpler  states  of  consciousness  ;  others  of  them,  as  the  sensations, 
of  muscular  weariness,  of  pain,  of  innervation,  and  "  local  coloring," 
may  possibly  have,  in  jDart,  a  central  origin.  As  a  rule,  they  lack 
the  characteristic  quality  of  being  components  of  the  "  presenta- 
tions of  sense,"  as  this  quality  belongs  to  all  genuine  sensations. 
Sensations  of  "local  coloring"  have,  indeed,  a  most  important  part 
to  take  in  the  formation  of  the  "  presentations  of  sense  ; "  but  they 
are,  in  the  realm  of  touch  and  of  muscular  feeling,  as  infinitely  and 
delicately  varied  (and  even  more  difficult  of  description)  as  are  the 
finest  shadings  of  musical  tones  or  color-tones. 

§  20.  A  sixth  sense,  however,  and  a  sixth  organ  of  sensations 
must  doubtless  be  recognized  as  constituted  by  the  muscles  and 
the  various  kinds  of  feeling  which  their  action  occasions.  These 
muscular  sensations,  when  combined  with  those  of  the  skin,  give 
certain  complex  feelings  of  motion  on  which  the  adjustment  of  the 
body  to  its  environment  is  so  dependent.  The  long-continued  dis- 
pute concerning  the  presence  of  sensory  nerve-fibrils  in  the  muscles 
may  be  said  to  be  settled  affirmatively. '^  Certain  subjective  phe- 
nomena cannot  be  accounted  for  by  ascribing  the  so-called  muscular 
sensations  to  feelings  of  central  innervation,  or  by  identifying  them 

'  On  the  physiology  of  the  skin,  see  Goldscheider,  art.  Neue  Thatsachen 
liber  die  Hautsinnesnerven,  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth., 
Supplement-Band,  pp.  1-104. 

^  See,  especially,  Sachs,  iu  Archiv  f.  Anat.  u.  Physiol.,  1874,  pp.  175  f.,  491 
f . ,  and  645  f . 


THE   FEELING   OF   PRESSURE.  345 

with  the  sensations  of  pressure  through  the  skin. '  Bernhardt "  found 
that  the  degree  of  sensitiveness  to  different  weights,  when  lifted  by 
the  foot  or  the  finger,  was  little  or  not  at  all  diminished  by  exclud- 
ing all  central  innervation  of  the  muscles  through  an  act  of  will. 
The  discrimination  of  differences  of  weight  was  not  greatly  impaired 
when  the  limb  was  bent  by  an  induction -shock  sent  through  the 
muscles  instead  of  by  motor  impulses  arising  in  the  brain.  The 
muscular  sensations  cannot,  therefore,  be  due  to  such  central  activ- 
ity. Investigation  also  shows  that  the  muscular  sensations  sup- 
plement those  of  pressure  in  the  skin  in  all  our  estimates  of  the 
position  and  motion  of  the  limbs  ;  these  two  are,  therefore,  not 
identical.  Moreover,  without  assuming  the  existence  and  aid  of 
such  sensations  we  cannot  account  for  that  nice  control  of  the  mus- 
cles which,  especially  in  the  case  of  the  eye,  is  so  indispensable  a 
prerequisite,  not  only  for  adjusting  their  action  to  the  ends  desired, 
but  also  for  gaining  an  exact  knowledge  of  the  position  and  motion 
of  objects  in  the  outside  world.  The  precise  manner,  however,  in 
which  the  muscular  sensations  originate,  through  that  stimulation 
of  the  sensory  nerves  which  the  contraction  of  the  muscular  fibre 
occasions,  is  as  yet  unknown.  Nor  can  they  easily  be  separated 
and  classified  into  kinds,  apart  from  the  sensations  of  pressure  with 
which  they  are  in  actual  experience  constantly  allied.  Their  chief 
interest  to  psychology  centres  in  the  help  which  they  furnish  to  the 
mind  in  forming  itfe  "  presentations  of  sense." 

§  21,  Sensations  of  Pressure  are  dependent  upon  the  excitation 
of  the  sensory  nerves  of  the  skin  through  their  appropriate  end- 
orgfins.  The  excitation  of  the  trunk  of  any  of  these  nerves  at  some 
point  along  its  course  may  produce  the  feeling  of  pain,  but  does  not 
produce  those  definite  sensations  of  pressure  which  we  are  able  to 
localize  so  accurately  and  discriminate  so  nicely  as  to  their  degree. 
Precisely  which  of  these  end-organs  are  specifically  related  to  sen- 
sations of  pressure  neither  histology  nor  experimental  physiology 
has  thus  far  been  able  to  determine  (see  Part  I.,  chap.  V.,  §  10), 
The  ordinary  stimulus  of  the  end-organs  of  the  skin  active  in  these 
sensations  consists  in  their  compression  or  expansion  by  contact 
with  some  external  object  which  either  rests  upon  them  or  upoa 
which  they  rest,  or  which  is  moved  over  or  against  them,  or  over  or 
against  which  they  are  moved.  Such  stimulus  may,  of  course,  vary 
both  in  form  and  in  degree.  The  quantity  and  succession  of  the 
sensations  of  pressure,  as  well  as  the  manner  in  which  they  com- 
bine with  one  another  and  with  sensations  of  the  muscular  sense, 

'  Comp.  Funke,  in  Hermann's  Handb.  d.  Physiol.,  III.,  ii, ,  p.  359  f. 
2  Archiv  f .  Psychiatrie,  III. ,  p.  627. 


346  SENSATiOTsrs  or  the  skin. 

have  a  marked  effect  in  determining  their  characteristic  "tone" 
of  feeling.  In  respect  to  quality  pure  and  simple,  sensations  of 
pressure  scarcely  admit  of  a  scientific  classification.  We  localize 
them  in  the  field  of  touch  ;  we  make  an  important  use  of  them  in 
connection  with  sensations  of  muscular  origin,  for  constructing  the 
field  of  vision  and  for  giving  to  different  objects  their  respective 
places  in  this  field  ;  but  in  ordinary  experience  we  do  not  directly 
recognize  kinds  of  the  simple  sensations  of  pressure  as  we  do  of 
tastes,  smells,  tones,  and  colors.  A  distinction  is  sometimes  made 
between  "  light  touch,"  or  touch  proper,  and  sensations  of  press- 
ure or  weight.  But  the  distinction,  so  far  as  it  leaves  out  of  ac- 
count the  muscular  sensations,  has  hitherto  been  one  only  of  de- 
gree and  not  of  kind. 

The  more  recent  and  thorough  investigations  of  Goldscheider  * 
have  led  him  to  distinguish  two  si^ecifically  different  sensations 
which  enter  into  what  is  ordinarily  called  the  feeling  of  pressure. 
This  distinction  is  based  upon  facts  experimentally  ascertained.  If 
a  very  fine  point  of  metal,  wood,  or  cork,  be  touched  lightly  to  the 
skin,  it  will  be  found  to  awaken  a  definite  sensation,  such  as  is  en- 
titled to  be  called  a"  sensation  of  pressure,"  only  at  certain  minute 
spots  in  any  given  area  of  the  skin.  This  sensation,  when  the 
pressure  is  very  light,  is  described  as  lively  and  delicate,  often 
accompanied  by  the  feeling  of  being  tickled.  On  increasing  the 
pressure  upon  these  same  spots  the  sensations  change  their  char- 
acter somewhat,  and  become  as  though  some  small,  hard  kernel 
were  pressed  uj)on  the  skin  ("  Kdrniges  Gefnhl  ").  Between  these 
distinctively  "pressure-spots"  it  is  not  possible  to  excite  by  i^ress- 
ure  the  same  characteristic  sensation.  Stimulation  of  the  inter- 
mediate spots,  on  the  contrary,  produces  a  dull,  indefinable,  "con- 
tent-less "  sensation  ;  and  when  the  pressure  is  increased,  a  sense 
of  being  pricked  or  stuck.  Both  of  these  kinds  of  sensation,  when 
the  pressure  is  still  further  increased,  pass  over  into  painful  feeling  ; 
but  the  character  of  the  pain  in  the  two  is  different. 

The  arrangement  of  the  "  pressure-spots  "  is  analogous  to  that  of 
the  temperature-spots  (to  be  described  subsequently).  They  occur 
much  more  frequently  in  certain  areas  of  the  body  than  in  others. 
They  are  placed  in  chains,  as  it  were,  sometimes  more  and  some- 
times less  thickly  set.  These  chains  ordinarily  radiate  from  a  kind 
of  central  point,  and  run  in  such  directions  as  to  form  either  circu- 
lar, longitudinal,  or  pyramidal  figures.  Their  direction  is  seldom 
identical  with  that  of  the  temperature-spots.      In  tlie  opinion  of 

'  Archiv  f.  Anat,  u,  Physiol.,  1885,  Pliysiolog.  Abth.,  Supplement-Band,  pp. 
76  fE. 


ARRANGEMENT   OF   PRESSURE-SPOTS. 


347 


Goldscheider  the  spots  of  both  kinds  correspond  to  the  terminal 
points  of  the  nerve-fibres  of  two  specifically  different  kinds  of  nerves 
distributed  over  the  skin.  But  whereas  aU  the  area  of  the  skin  is 
well  covered  with  such  nerves  as  give  us  the  general  dull  and  in- 
definite feeling  of  contact,  the  nerves  of  the  sensation  of  pressure 
are  much  more  unevenly  distributed.  It  need  scarcely  be  said 
that,  other  things  being  equal,  they  are  most  numerous  in  the  areas 
of  the  skin  most  sensitive  to  touch.  The  different  pressure-spots 
themselves  differ  in  sensitiveness  ;  some  are  much  more  easily  ex- 
cited than  others.      The  sensations  themselves  come  under  the 


.'^jmm- 


Fig.  95.— Arrangement  of  Pressure- spots  (Goldscheicler).  A,  dorsal  and  radial  surface  of  the 
first  phalanx  of  the  Index  fioger ;  B,  membrane  between  thumb  and  index  finger;  0,  dorsal 
surface  of  forearm ;  D,  back ;  B,  inner  surface  of  forearm  ;  F,  back  of  hand. 

general  laws  of  exhaustion,  practice,  etc.,  as  these  laws  apply  to 
the  whole  mechanism  of  sense. 

The  attempt  has  been  made,  on  the  other  hand,  to  identify,  in 
kind,  sensations  of  pressure  (especially  those  of  light  touch)  and 
sensations  of  temperature.'  E.  H.  Weber  observed  that  cold  bodies 
resting  on  the  skin  appear  heavier,  and  warm  lighter,  than  they 
really  are.  A  single  silver  dollar  of  the  temperature  of  25°-19.5° 
Fahr.  appeared  to  be  of  the  same  weight  as  two  dollars  of  the  tem- 
perature of  98.5°-100.5°  Fahr.  Wunderli  also  argues  the  identity 
of  these  two  classes  of  sensations  on  the  ground  that,  if  certain  parts 
of  the  skin  are  lightly  touched  with  cotton  or  slightly  warmed  by 
approaching  a  heated  surface  to  them,  through  a  square  opening  in 

'  For  a  discussion  of  this  qiiestion,  see  Funke,  in  Hermann's  Handb.  d. 
Physiol.,  III.,  ii.,  p.  B20  f. 


348  SENSATIONS   OF   THE  SKIN. 

a  piece  of  paper  laid  upon  the  skin,  the  two  sensations  thus  occa- 
sioned are  frequently  mistaken  for  each  other.  But  Szabadfoldi 
has  much  Aveakened  the  force  of  Weber's  experiment  by  showing 
that  small  wooden  disks  when  heated  to  122°  Fahr.  often  feel 
heavier  than  those  which  are  really  larger  but  are  not  thus  warmed. 
And  Wunderli's  observation  at  best  holds  good  only  for  compara- 
tively obtuse  parts  of  the  skin,  especially  the  back.  Moreover,  if 
the  same  stimuli  should  serve  to  excite  both  the  pressure-spots 
and  the  temperature-spots,  this  would  not  prove  the  identity  of  the 
two  sensations. 

Finally,  the  physiology  of  the  sense  of  temperature  re-enforces 
the  indubitable  testimony  of  consciousness,  and  leads  us  to  the  con- 
clusion that  from  beginning  to  end — in  the  character  of  their  stimuli, 
of  their  nervous  processes,  and  of  the  resulting  modifications  of 
feeling — the  sensations  of  pressure  and  the  sensations  of  tempera- 
ture are  qualitatively  distinct.  They  have  in  common  only  the 
organ  in  which  their  apparatus  is  located,  and  the  fact  that  both 
kinds  of  sensations  are  constantly  associated  most  intimately  in 
time  and  space. 

§  22.  Sensations  of  Temperature,  therefore,  form  a  second  dis- 
tinct species  which  have  their  origin  in  the  excitation  of  the  nervous 
end-apparatus  of  the  skin.  Whether  their  end-apparatus  is  locally 
the  same  as  that  upon  the  excitation  of  which  the  sensations  of 
pressure  are  dependent,  it  has  seemed  rmtil  very  lately  impossible 
to  say.  But  recent  investigations  (especially  of  Blix,'  Goldscheider,'' 
and  Donaldson')  point  unequivocally  to  the  conclusion  that  certain 
definite  spots  of  the  skin,  and  these  only,  are  susceptible  to  irrita- 
tions of  a  kind  to  result  in  sensations  of  temperature.  Such  spots 
are  insensible  to  pain  (even  the  pain  of  temperature),  and  a  needle 
can  be  run  into  them  without  being  felt ;  they  are  probably  also  in- 
sensible to  pressure.  What  is  more  remarkable  still,  the  existence 
of  "  heat-spots  "  and  "  cold-spots  " — or  minute  localities  of  the  skin 
sensitive  to  heat  but  not  to  cold,  and  conversely — seems  demon- 
strable. By  using  a  machine  which  locates  the  stimulus  micro- 
metrically,  the  topography  of  the  skin  may  be  mapped  out,  and 
extremely  minute  spots  indicated  which  respond  to  irritation  with 
sensations  of  pain,  of  pressure,  of  cold,  and  of  heat — respectively. 
These  different  kinds  of  sensation-spots  appear  never  to  be  super- 

'  Zeitschrift  f.  Biol.,  1884,  XX.,  pp.  141  ff. 

^  Moiiatshefte  f.  prakt.  Dermatol.,  1884,  III.,  Nos.  7,  9, 10  ;  1885,  IV.,  No.  1 ; 
and  art.  in  Archiv  f.  Anat.  u.  Pliysiol.,  1885,  Physiolog.  Abtli.,  Supplement- 
Band. 

^  Reseai'ch  on  the  Temperature-sense,  reprinted  from  Mind,  No.  XXXIX. 


AKRAiSGEMENT   OF   TEMPERATUEE-SPOTS.  349 

imposed.  They  are  not  located  alike  on  the  symmetrical  parts  oi 
the  same  individual,  or  on  the  corresponding  parts  of  different  in- 
dividuals. An  accurate  mapping  out  of  the  different  areas  of  the 
skin,  with  respect  to  their  temperatui'e-spots,  is  difficult ;  since  ex- 
periment soon  blunts  the  sense,  and  even  the  approach  of  a  heated 
or  cooled  point  raises  or  lowers  the  temperature  over  a  considerable 
area.  But,  in  general,  such  spots  occur  in  lines  that  radiate  from 
centres  generally  coincident  with  the  roots  of  the  hairs,  in  those 


Fig.  9C.— Arrangement  of  Temperature-spots.     A,  heat-spots ;   and  B,  cold- spots— from  the  palm 
of  the  left  hand  (GoMsoheider). 

regions  of  the  skin  where  such  appendages  are  found.  These  lines 
often  run  so  as  to  cross  each  other,  forming  figures  of  various  shapes, 
— triangles  with  rounded  corners,  etc.  Heat-spots  are,  on  the 
whole,  less  abundant  than  cold-spots  ;  but  inpartsof  the  body  where 
the  skin  is  most  sensitive  to  either  heat  or  cold  the  corresponding 
class  of  sjDots  is  relatively  frequent.  Temperature-spots  may  be 
divided  into  first-class  and  second-class  (so  Goldscheider)  according 
to  the  strength  with  which  they  react  on  moderate  stimulation. 
Some  spots  are  roused  only  by  excessive  temperatures.  The  same 
object  feels  cool  to  one  spot,  ice-cold  to  another. 

The  electrical  current  when  applied  to  these  spots  is  thought  to 
call  out  the  corresponding  specific  sensations.  Goldscheider  con- 
siders that  he  has  succeeded  in  exciting  definite  temperature-sensa- 
tions by  applying  electricity  to  the  trunks  of  the  nerv'es  distributed 
to  certain  areas  of  the  skin.  This  would  appear  to  be  almost  a 
demonstration  that  the  nerves  of  this  sense  are  specific,  and  of 
two  kinds — nerves  of  heat-sensation  and  nerves  of  cold-sensation. 
Puncturing  a  temperature-spot  also  gives  rise  to  temperature-sen- 
sations. The  discriminative  sensibility  of  the  temperature-spots 
is  found  to  be  much  finer  than  that  of  the  tactile  sensations. 
Everything  which  produces  a  change  in  the  temperature  of  the 
skin  acts,  of  course,  as  a  stimulus  for  the  sensations  of  heat  and 
cold. 

§  23.  The  above-mentioned  discoveries  as  to  the  specific  energy 
of  the  nerves  and  end-apparatus  of  the  skin,  interesting  as  they  are. 


350  SENSATIONS   OF   THE   SKIN. 

have  not  yet  been  completely  brougiit  into  rational  connection  with 
our  experience  of  temperature-sensations  and  our  knowledge  of 
the  general  laws  of  nervous  action.  It  is  obvious,  however,  "^iat 
the  principles  of  contrast,  of  relativity,  and  of  exhaustion,  must 
bear  a  large  part  in  the  explanation  of  all  these  sensations.  Sen- 
sations of  temperature  have  apparently  a  certain  dependence  on 
the  temperature  of  the  thermic  apparatus  itself.  This  law  has  been 
elaborated  and  defended  in  detail  by  Hering,'  in  the  following 
form  :  "  As  often  as  the  thermic  apparatus  at  any  spot  in  the 
skin  has  a  temperature  which  lies  above  its  own  zero-point  we 
have  a  sensation  of  heat ;  in  the  contrary  case,  a  sensation  of  cold. 
Either  sensation  is  so  much  the  more  marked,  or  stronger,  the 
more  the  temperature  of  the  thermic  appai-atus  at  the  time  varies 
from  the  temperature  of  its  own  zero-point."  By  the  "zero-point" 
of  any  part  of  the  skin  is  meant  the  exact  objective  temperature 
which  at  that  part  will  produce  no  sensation  of  either  heat  or  cold. 
Such  zero-point  is,  of  course,  different  for  different  parts  of  the 
body,  according  as  they  are  or  are  not  exposed,  and  are  or  are  not 
well  supplied  with  arterial  blood,  etc.  It  also  changes  in  connection 
with  changes  in  the  temperature  of  the  surrounding  air  or  of  the 
bodies  with  which  the  skin  is  in  contact.  By  this  principle  a  great 
number  of  our  ordinary  sensations  of  temperature  are  explained 
by  Hering.  The  finger  and  the  nose  are  colder  than  the  inside 
of  the  mouth,  because  they  are  exposed  to  radiation  of  their  heat. 
On  passing  from  a  room  of  a  given  temperature  into  one  of  either 
higher  or  lower  temperature  we  experience  at  first  certain  sensa- 
tions of  temperature  while  the  zero-point  of  the  thermic  apparatus 
is  becoming  adjusted  to  its  new  surroundings.  After  such  adjust- 
ment has  taken  place  these  sensations  may  cease — to  be  renewed 
in  the  revei'se  direction,  however,  on  a  return  to  the  former  sur- 
roundings. This  adjustment  has  its  limits  ;  it  is  dependent  chiefly 
upon  the  evaporation  of  the  skin  and  upon  the  circulation  of  the 
blood. 

If  the  surroundings  are  more  than  so  hot  or  so  cold,  they  may 
excite  constant  sensations  of  temperature.  Among  the  induce- 
ments to  sensations  of  heat  at  any  locality  of  the  skin,  Hering  men- 
tions the  following  as  prominent  in  our  ordinary  experience  :  All 
checking  of  the  radiation  of  heat,  while  the  blood-supply  remains 
unaltered  ;  all  contact  with  a  medium  or  object  of  higher  tem- 
perature— and  this  according  to  the  ease  with  which  such  medium 
or  object  parts  with  its  heat ;  and  all  increase  of  heat  in  the  skin 

'  In  Hermann's Haiidb.  d.  Physiol.,  III.,  ii.,  p.  419  f . ;  and  Sitzgsber.  d. Wie- 
ner Acad.,  LXXV.,  Abth.  3,  p.  101  f. 


DETERMINATION   OF   THE   ZERO-POINT.  351 

coming  from  the  interior  of  the  body,  as  in  the  sudden  hj'pergemia 
which  takes  place  in  blushing.  Inducements  to  sensations  of  cold 
are  as  foUows  :  Increased  convection  of  the  heat  of  the  skin  by  the 
suiTounding  medium,  while  the  blood-supply  remains  unchanged 
(as  when  the  wind  blows  over  the  hand  or  face,  esj)ecially  if  the 
skin  be  moist)  ;  contact  with  objects  which  have  the  same  (or  even 
slightly  higher)  objective  temperature  as  the  surrounding  air,  but 
convey  the  heat  from  the  skin  more  rapidly  than  it  ;  contact  with 
or  j)roximity  to  objects  colder  than  the  skin  ;  lessening  of  the 
interior  warmth  of  the  body — for  example,  by  contraction  of  the 
blood-vessels  which  supply  a  given  portion  of  the  skin.  Ordinary 
experience  makes  us  famihar  with  many  of  the  phenomena  which 
come  under  all  these  cases. 

The  determination  of  the  e'K^act  zero-point  of  different  parts  of  the 
body  is  a  matter  of  great  difficulty.  The  rise  and  fall  of  the  tem- 
perature of  the  thermic  apparatus,  in  connection  with  that  principle 
of  exhaustion  which  aj^plies  to  all  the  nervous  mechanism,  and  es- 
pecially to  certain  of  the  end-organs  of  sense,  doubtless  account 
(at  least  partially)  in  some  way  for  the  well-known  phenomena  of 
contrast  in  temperature-sensations.  "Weber  showed  that  if  the 
hand  be  held  for  a  minute  in  water  of  the  temperature  54.5° 
Fahr.,  and  then  in  water  of  64.4"  Fahi*.,  a  sensation  of  heat  will  be 
felt  for  a  few  seconds,  although  the  latter  would  have  felt  cold  to 
the  hand  if  placed  in  it  at  first.  Moreover,  if  we  hold  one  hand  in 
moderately  cold  water,  and  dip  the  other  repeatedly  in  the  same 
water,  the  sensation  of  cold  is  stronger  in  the  latter,  although  the 
temperature  of  the  hand  held  in  the  water  is  really  lower.  But, 
according  to  an  experiment  of  Goldscheider's,  if  one  hand  be  left 
for  ten  seconds  in  water  of  the  temperature  of  104°  Fahr.,  and  then 
both  hands  immersed  in  cold  water,  the  warmed  hand  will  feel  the 
cold  less  distinctly  than  the  other.  This  latter  investigator,  how- 
ever, is  inclined  to  dissent  from  Hering's  theory,  and  retui-n  to  the 
theory  of  E.  H.  Weber.  "Weber  held  that  the  rising  of  the  tem- 
perature of  the  skin  is  felt  as  heat,  and  its  sinking  as  cold. 

After-images  of  temperature-sensations  seem  also  to  exist.  But 
when  a  surface  of  the  skin  has  been  warmed  or  cooled,  and  the 
after-image  has  faded  quite  away,  it  is  said  that  it  can  be  called 
back  b}'  light  mechanical  irritation  ;  this  is  especially  true  of  sen- 
sations of  cold.  The  phenomena  of  exhaustion  are  noticed  in  sen- 
sations of  tempei'ature.  Our  perception  of  the  absolute  degree  of 
temperature,  and  of  minute  variations  in  its  degree,  is  most  acute 
for  places  in  the  scale  lying  close  to  the  normal  temperature  of  the 
skin.     It  would  seem,  on  the  whole,  as  though   the  phenomena 


352  SENSATIONS    OF   THE   SKIN. 

of  contrast  of  sensations  of  temperature,  as  well  as  of  color,  require 
for  their  satisfactory  explanation  a  knowledge  (possibly  of  the 
action  of  the  central  organs  of  the  nervous  system)  which  we  do 
not  yet  possess. 

E.  H.  Weber  also  showed  that  the  amount  of  the  skin  which  is 
stimulated  has  a  marked  influence  on  the  quality  of  the  resulting 
sensation.  The  temperature  of  the  same  fluid  does  not  feel  pre- 
cisely the  same  to  a  single  finger  and  to  the  entire  hand.  This 
experience  is  similar  to  that  which  has  already  been  described  in 
the  case  of  sensations  of  color.  It  appears  explicable  in  the  case 
of  the  skin  from  what  is  now  known  about  the  existence  of  a  cer- 
tain variable  number  of  heat-sjDots  and  cold-spots.  In  the  same 
way,  in  part,  may  we  explain  the  fact  that  smooth  objects,  which 
therefore  come  into  contact  with  a  larger  portion  of  the  skin — like 
leather,  paper,  wood,  glass,  and  porcelain — appear  colder  to  the 
whole  hand  even  when  they  have  the  same  objective  temperature 
with  it. 

§  24.  Nothing  whatever  is  known  as  to  the  exact  manner  in  which 
changes  of  temperature  act  upon  the  thermic  apparatus  to  excite 
it  ;  the  recent  discoveries  ajDpear  to  make  such  action  all  the  more 
difficult  of  conception  and  description.  Since  the  terms  "  hot " 
and  "  cold  "  are  in  physics  only  relative,  it  is  hard  to  see  why  ab- 
solutely different  apparatus,  with  a  distinct  local  position,  should 
be  used  (as  Goldscheider's  discoveries  indicate)  for  the  sensations 
corresponding  to  each.  Moreover,  on  Hering's  hypothesis,  how 
are  we  to  account  for  the  fact  that  heat-spots  and  cold-spots  are  in 
turn  stimulated  by  the  same  objective  temperature  according  to 
the  rise  and  fall  of  the  zero-point  of  tbe  entire  region  of  the  skin  ? 
Possibly  it  may  be  found  that  certain  chemical  or  electrical  changes, 
dependent  upon  the  increase  or  decrease  of  that  mode  of  molecular 
motion  which  jDhysics  calls  "  heat,"  are  the  proximate  stimuli  of 
the  two  classes  of  end-organs  of  the  temperature-sense.  Gold- 
scheider  supposes  that  the  difference  in  sensitiveness  of  different 
areas  of  the  skin  to  temperature  must  be  ascribed  to  the  anatomi- 
cal distribution  of  the  heat- sensitive  and  cold-sensitive  fibres,  re- 
spectively. But  he  does  not  show  us  what  kind  of  nervous  con- 
trivance would  satisfy  all  the  conditions  which  are  imposed  by  the 
complicated  facts  of  experience. 

A-  Herzen  '  considers  himself  to  have  demonstrated,  by  patho- 
logical cases  and  experiment  upon  animals,  that  sensory  impulses 
of  cold,  like  those  of  touch,  pass  along  the  posterior  strands  of  the 
spinal  cord  ;  and  that  the  sanje  region  of  the  brain  {Gyrus  sigmot- 
'  See  Pfliiger's  Archiv,  1885,  pp.  93  fE. 


'SPECIFIC   ENERGY   OF   THE   NERVES.  353 

deus)  is  the  "  centre  "  for  both.     Sensitiveness  to  heat  can  be  re- 
tained, it  would  seem,  after  sensitiveness  to  cold  has  been  lost. 

§25.  In  closing  the  subject  treated  in  the  last  two  chapters, 
attention  is  again  called  to  the  large  amount  and  cumulative  char- 
acter of  the  evidence  afforded  by  the  special  sensations,  considered 
as  respects  their  quality,  for  the  law  of  the  Specific  Energy  of  the 
Nerves.  It  is  impossible  to  account  for  the  above-mentioned  phe- 
nomena without  carrying  this  law  to  a  great  length  in  its  applica- 
tion to  the  special  senses.  We  may  not  be  able  to  affirm — as  does 
Fick,'  for  example — that  two  sensations  are  distinguishable  as  re- 
spects quality  only  in  case  they  are  occasioned  by  two  individually 
different  elements  of  the  nervous  system.  For  we  have  seen  that 
the  quality  of  sensations  depends  upon  their  quantity,  upon  their 
relation  to  preceding  and  contemporaneous  sensations,  and  upon 
considerations  other  than  merely  the  one  of  what  particular  nerve- 
fibre  or  element  of  the  end-apparatus  was  acted  upon  by  the  stim- 
ulus. Moreover,  there  is  no  warrant  for  saying  that  identically  the 
same  nervous  apparatus  cannot  be  excited  variously  according  to 
the  nature  of  the  stimulus  which  acts  upon  it,  or  according  to  the 
combination  with  other  parts  of  the  system  into  which  it  enters  for 
the  time.  It  is  obvious,  however,  that  the  differentiation  of  func- 
tion, and  the  assignment  to  specifically  distinct  apparatus  of  par- 
ticular nervous  impressions  corresponding  to  particular  mental 
states,  is  carried  to  a  great  length  in  the  special  senses.  In  this 
differentiation  of  function  it  is  not  wholly  or  chiefly  the  nerve- 
fibres,  as  such,  which  should  be  taken  into  account ;  it  is  also  the 
minute  subdivisions  of  the  eud-organsof  sense,  and  the  connections 
set  up  within  the  corresponding  regions  of  the  central  organs.  In 
accounting  for  those  complex  sensations  which  appear  in  ordinary 
consciousness,  the  law  of  permutations  and  combinations  has,  of 
course,  to  be  considered.  A  vast  variety  of  such  sensations  maybe 
made  up  by  changing  the  relations  to  each  other  of  comparatively 
few  simple  elements.  But  in  each  of  the  senses  our  analysis,  when 
carried  to  its  utmost  limit,  leaves  a  number — in  some  of  the  senses 
very  large — of  simple  sensations,  which  apparently  must  have  their 
physical  basis  in  the  excitation  of  specifically  distinct  elements  of 
the  nervous  mechanism. 

The  sense  of  smell  apparently  requires  that  the  law  of  the  specific 
energy  of  the  nerves  should  be  carried  to  such  a  length  as  almost 
to  reduce  it  to  an  absurdity.  Histology  has  discovered  only  one 
essential  kind  of  olfactory  end-organ,  and  that  of  comparatively 
simple  structure  ;  and  yet  experience  gives,  as  the  result  of  its  ex- 
1  In  Hermanns  Handb.  d.  Physiol.,  III.,  ii.,  p.  166. 
23 


354  SENSATIONS   OF   THE   SKIN". 

citation,  a  bewildering  variety  of  sensations  so  specifically  different 
as  to  baffle  all  our  attempts  to  classify  them.  From  the  case  of 
this  sense  an  argument  may  then  be  derived  which  leads  in  ei- 
ther direction.  It  may  be  objected  to  the  law  that  it  is  absurd  to 
sup23ose  a  complexity  of  the  end-organs  of  smell  such  as  to  corre- 
spond to  each  specific  kind  of  olfactory  stimulus  with  a  specific  sen- 
sation— for  example,  the  smell  of  musk,  or  of  sulphuretted  hydro- 
gen. It  may  be  replied  to  the  objection  that,  in  the  case  of  the 
ear,  there  are  at  least  16,000  or  20,000  distinct  forms  of  auditory 
end-apparatus  corresponding  to  the  different  musical  tones ;  and 
it  is  therefore  by  no  means  impossible  that  the  entire  regio  ol- 
factoria  may  contain  enough  siDecifically  different  forms  of  its  own 
peculiar  end-apparatus  to  suffice  for  all  the  simple  sensations  of 
smell. 

The  sense  of  taste  does  not  occasion  so  many  difficulties  in  rela- 
tion to  the  law  of  the  specific  energy  of  the  nerves.  It  is  thought 
possible  by  most  physiologists  to  reduce  all  the  sensations  of  taste 
to  four,  or  at  most  six,  different  species.  It  is  easy  to  suppose 
as  many  specifically  different  forms  of  the  nervous  apparatus  cor- 
responding to  the  different  classes  of  sensations — sweet  and  sour, 
salt  and  bitter,  alkaline  and  metallic.  In  spite  of  the  fact  that 
such  a  classification  appears  satisfactory  to  most  authorities,  experi- 
ence is  reluctant  to  confirm  it.  Many  of  the  complex  tastes,  even 
when  separated  from  their  accompanying  sensations  of  smell,  are 
scarcely  resolvable  into  combinations  of  the  above-mentioned 
simple  tastes.  Into  which  of  the  six,  for  example,  would  experi- 
ment resolve  the  gustatory  sensations  which  come  from  chewing  a 
bit  of  chocolate,  or  of  a  nut  from  a  black-walnut  tree  ? 

The  strongest  defence  of  the  most  extreme  form  of  the  theory  of 
the  specific  energy  of  the  nerves  has  hitherto  been  found  in  sensa- 
tions of  musical  sound.  Here  we  undoubtedly  have  a  wide  range 
of  qualitatively  distinct  states  of  consciousness  which  are  ap- 
parently dependent  ujDon  the  excitation  of  a  correspondingly  large 
number  of  distinct  nervous  elements.  From  sensations  of  sight, 
although  many  points  of  the  prevalent  theory  are  still  obscure  and 
unsatisfactory,  a  considerable  force  of  evidence  bearing  in  the  same 
direction  may  be  obtained.  It  seems  almost  certain  that  the 
numerous  states  of  consciousness  which  result  from  stimulating 
the  different  nervous  elements  of  the  retina  are  due  to  combina- 
tions of  a  comparatively  few  kinds  of  such  elements,  each  of  which 
responds  in  a  specific  way  to  a  special  order  of  stimulus.  Yet  this 
is  not  precisely  what  the  theory  of  specific  energy  seems  to  de- 
mand.    For  the  different  color-sensations  all  appear  as  simple  and 


•   SPECIFIC   ENERGY   OF  THE   NERVES.  355 

unanalyzable  states  of  consciousness.  None  of  them  are  twofold,  as 
sensations.  We  are  at  a  loss  to  say  why,  according  to  the  theory 
of  specific  energy,  each  sensation  should  not  result  from  the  ex- 
citation of  one,  and  only  one,  kind  of  nervous  elements. 

The  recent  discoveries  as  to  the  existence  of  pressure-spots, 
heat-spots,  and  cold-spots  in  the  skin  add  important  evidence  to 
that  ah-eady  existing  in  favor  of  the  law  under  discussion.  It  will 
further  appear,  when  we  consider  the  process  of  locaKzation  in  the 
so-called  "  geometrical  senses  "  of  the  eye  and  the  skin,  that  the 
very  possibility  of  such  a  process  demands  a  strict  and  far-reaching 
application  of  the  law  of  the  specific  energy  of  the  nerves.  Pre- 
cisely how  we  are  to  state  and  limit  this  law,  neither  its  opponents 
nor  its  advocates  have  as  yet  been  able  satisfactorily  to  show.  The 
exact  expression  of  the  theory  waits  for  further  evidence  from 
experiment,  although  there  can  be  little  doubt  that  in  its  main 
features  it  is  already  secure. 


CHAPTER  Y. 

THE  QUANTITY  OF  SENSATIONS. 

§  1.  By  an  act  of  mental  analysis,  which  all  men  readily  perform, 
changes  in  the  amount  of  sensation  are  distinguished  from  changes 
in  its  quality.  This  distinction  obviously  requires  for  its  perform- 
ance nothing  beyond  what  is  immediately  given  in  consciousness. 
All  sensations  appear  there  as  differing  among  themselves,  not  only 
with  respect  to  the  nature  of  the  impression  which  serves  to  classify 
them  into  groups  (as  sensations  of  sight,  sound,  etc.),  but  also  with 
respect  to  the  degree  in  which  each  particular  impression  possesses 
the  sphere  of  conscious  attention  and  feeling.  The  best  illustra- 
tion of  an  alteration  in  the  intensity  of  sensation,  while  its  charac- 
teristic quality  remains  unaltered,  may  be  derived  from  musical 
tones.  The  dying-out  of  a  single  note  when  the  bow  is  drawn 
with  decreasing  force  across  the  string  of  a  violin,  or  a  single 
key  of  the  piano  is  struck  and  the  pedal  held,  may  be  considered 
as  a  change  in  the  quantity  of  sensation,  while  its  quality  is  un- 
changed. A  more  complex  case  is  the  experience  we  have  when 
approaching  to,  or  receding  from,  a  bell  that  is  sounding  or  a 
steam-whistle  that  is  blowing.  Noises  of  a  certain  complex  quality 
— such  as  slamming,  hissing,  grating,  etc. — are  continually  de- 
scribed as  very  loud,  moderately  loud,  or  of  weak  intensity.  So, 
too,  when  approaching  a  white  or  colored  light,  with  our  attention 
fixed  upon  it,  we  generally  disregard  almost  wholly  the  changes 
in  its  color-tone  which  take  place,  and  consider  chiefly  the  changes 
in  its  intensity  and  apparent  size.  The  pressure  of  diffei'ent 
weights  upon  different  parts  of  our  skin  is  ordinarily  regarded  as 
the  same  in  quality  and  as  varying  only  in  amount  and  locality. 
The  same  thing  is  true,  in  almost  precisely  the  same  way,  with 
sensations  of  temperature.  The  thing  we  touch  is  called  slightly 
cold  or  very  cold,  somewhat  warm  or  hot,  our  attention  being 
directed  chiefly  to  the  quantum  of  sensation  which  it  calls  forth. 
In  other  words,  it  is  generally  the  same  kind  of  pressure  and  tem- 
perature, with  a  varying  degree  of  intensity,  of  which  we  are 
conscious. 


QUAISTTITY   ATSTD   QUALITY.  357 

It  Is  more  difficult,  however,  even  in  the  most  indefinite  way,  to 
separate  the  quantities  of  our  sensations  of  smell  and  taste  from 
the  changes  in  quality  of  the  same  sensations.  A  concentrated 
sweet  or  acid  so  strongly  excites  a  variet}^  of  forms  of  feeling  which 
mingle  indistinguishably  with  the  specific  sensations  of  taste  that 
we  are  compelled  to  attend  to  the  very  decided  qualitative  changes 
which  are  taking  place.  The  increased  intensity  of  the  sweet  or 
sour  we  may  indeed  speak  of  as  "very"  much  of  the  same  sensa- 
tion which  was  excited  in  less  degree  by  the  diluted  form  of  the 
stimulus ;  but  we  are  more  likely  to  regard  it  as  constituting  a 
complete  change  in  the  kind  of  taste.  In  the  same  manner,  atten- 
tion is  forcibly  directed  toward  the  kind  of  sensation  which  results 
from  increasing  the  quantity  of  any  specific  sensation  of  smell. 

It  is  further  obvious  that  the  distinction  which  we  make  between 
changes  in  the  quantity  and  changes  in  the  quality  of  our  sensa- 
tions is  to  some  extent  applicable  for  comparing  the  sensations  of 
different  senses.  And  here  the  distinction,  when  applied  to  sub- 
species under  certain  specific  forms  of  sensation,  affords  us  a 
means  of  transition  for  such  comparisons.  Some  yellows  are 
bright  and  others  dull ;  and  the  same  thing  is  true  of  the  reds  and 
the  blues.  The  sours,  the  sweets,  the  bitters,  may  be  compared 
with  each  other  as  respects  the  degree  of  intensity  which  they  pos- 
sess. We  may  next,  in  a  very  indefinite  way,  compare  the  quantities 
of  the  sensations  of  the  different  senses  as  they  appear  side  by  side, 
or  successively,  in  consciousness.  We  are  ordinarily  satisfied, 
however,  with  simply  describing  the  varying  degrees  of  intensity 
possessed  by  our  different  sensations  as  "  weak  "  or  "  strong  "  (with 
or  without  the  emphatic  "  very  "),  or  as  only  "  moderate."  Thus 
we  may  judge  that  both  the  light  which  we  see  and  the  tone  which 
we  hear  (either  simultaneously  or  one  immediately  after  the  other) 
are,  or  are  not,  to  be  classed  together  under  the  same  one  of  these 
three  grades  of  intensity. 

§  2.  That  changes  in  the  intensity  of  our  sensations  are  not,  in 
fact,  independent  of  changes  in  their  specific  nature  has  already 
been  proved  (Chap.  TV".,  §  4).  Only  in  the  case  of  musical  tones 
are  we  able  at  the  same  time  to  attend  carefully  to  both  the  quan- 
tity and  quality  of  our'  sensations,  and  so  discover  with  perfect 
confidence  that  the  former  is  changing  while  the  latter  remains  un- 
changed. Even  in  this  case,  since  the  tones  which  we  ordinarily 
hear  are  composite,  any  considerable  alteration  of  their  intensity 
changes  also  their  tone-coloring,  through  the  alteration  which  it 
produces  in  the  comparative  intensities  of  the  overtones.  Any  in- 
crease iu  the  brightness  of  a  particular  color  invariably  changes  its 


358  MEASUKEMENT   OF   SENSATIOTSTS. 

characteristic  color-tone.  A  white  of  less  intensity  is  not  merely 
less  white,  but  becomes  a  gray  ;  and  by  constantly  diminishing  its 
intensity  white  can  be  shaded  through  the  different  grays  toward 
black,  which  is  certainly  not  a  feebler  degree  of  the  sensation  of 
white.  The  same  dependence  of  quality  on  quantity  is  true  in  all 
sensations  of  smell,  taste,  pressure,  and  temperature.  It  would  be 
a  mistake,  however,  on  this  account  to  consider  "  quantity  "  of  sen- 
sations as  only  another  name  for  shades  of  quality,  or  to  deny  that 
we  can  apply  terms  of  measurement  to  these  reactions  of  the  mind 
upon  the  excitation  of  the  nervous  apparatus  of  sense.'  Scientific 
analysis  confirms  the  distinction  made  by  ordinary  experience  be- 
tween "the  way"  we  feel  and  "how  much"  we  feel  in  any  particular 
way. 

§  3.  All  descriptions  of  the  changing  intensities  of  sensations, 
when  made  on  the  basis  of  ordinary  experience  solely,  leave  the 
subject  in  a  very  indefinite  and  unscientific  form.  That  a  certain 
noise  is  louder  or  weaker  than  another  of  precisely  the  same  kind, 
one  may  be  quite  ready  to  afiirm  ;  one  may  even  be  ready  to  say 
that  one  judges  this  noise  to  be  about  twice  or  three  times  as  loud 
as  the  other.  But  when  more  precise  estimates  are  demanded,  one 
is  obliged  to  hesitate  before  giving  them.  Is  this  musical  tone  ten 
(or  a  hundred)  times  as  loud  as  the  other  ;  or  is  it  only  nine  and 
nine-tenths  (or  ninety-nine  and  nine-tenths)  as  loud  ?  Few  would 
venture  so  nice  an  estimate  with  any  confidence.  Yet  the  case  of 
sound  is  much  more  favorable  than  that  of  most  of  the  senses  for 
forming  an  exact  judgment  as  to  its  intensity.  It  would  be  difficult 
under  the  most  favorable  circumstances  to  affirm  that  the  sensa- 
tion of  the  light  a  is  twice  or  three  times  as  bright  as  that  of  the 
light  h  ;  or  that  of  the  shadow  x  one-half  or  one-third  as  bright  as 
y.  The  comparative  intensities  of  different  color-tones  are  yet  more 
difficult  to  fix  subjectively — even  in  the  most  indefinite  way.  This 
particular  yellow  may  seem  about  as  bright  a  color,  of  its  kind,  as 
does  the  red  near  it,  of  its  kind.  But  the  precise  moment  could 
not  readily  be  told  when  the  blue  of  the  sky  appears  exactly 
twice  as  intense  as  the  green  of  the  grass.  Still  further,  all  esti- 
mates of  the  quantity  of  sensation  approach  the  point  at  which 
they  lose  their  meaning  and  tend  to  become  absurd,  when  we  com- 
pare, for  example,  sensations  of  smell  or  taste  with  those  of  press- 
ure, temperature,  or  sight.  We  never  say  :  The  rose  smells  as 
sweet  as  it  looks  red  ;  or  the  lemon  is  twice  as  sour  as  the  sky  is 
blue.  And  yet  each  qualitatively  different  sensation  is  assumed  to 
have  its  place  somewhere  in  that  scale  of  intensities  through  which 
'  Comp.  Ktumi)i',  Ton  psychologic,  I.,  p.  347  f. 


PEOBLEMS   OF   QUANTITY.  359 

the  different  qualities  may  run  ;  each  may,  therefore,  be  compared 
with  every  other,  with  respect  to  the  general  position  which  it  oc- 
cupies in  its  characteristic  scale. 

§  4.  All  things  to  which  terms  of  quantity  apply  admit  of  some 
kind  of  measurement  and  comparison  with  respect  to  their  quantity. 
Sensations,  to  be  sure,  are  not  "things,"  but  rather  modes  of  the  ac- 
tivity of  mind,  excited  through  the  nervous  mechanism  of  sense. 
Nevertheless,  since,  like  material  things,  they  admit  of  some  appli- 
cation to  themselves  of  the  terms  of  quantity  ;  and  since  they  vary 
in  their  absolute  and  relative  degrees  of  quantity,  it  is  not  strange 
that  experimental  science  has  endeavored  to  measure  sensations, 
and  to  state  laws  for  their  comparison  and  mutual  relations.  The 
general  question  of  the  quantity  of  sensation  involves  an  answer  to 
two  subordinate  inquiries.  Of  these  two  the  first  concerns  the 
limits  within  which  the  different  sensations  may  vaiy  in  quantity, 
and  yet  remain  sensations  of  the  same  sense  ;  the  second  concerns 
the  law  of  the  relation  which  is  maintained  within  the  limits  among 
the  various  sensations  compared.  But  neither  of  these  questions 
can  be  answered  directly.  Sensations  cannot  be  kept  constant  in 
quantit}-,  and  measured  by  the  direct  application  of  physical  stand- 
ards, whether  with  a  view  to  fix  their  absolute  or  their  relative 
magnitude.  They  are  all,  however,  under  ordinary  circumstances, 
connected  with  the  action  of  different  forms  of  physical  energy 
upon  the  nervous  system  ;  that  is  to  say,  they  are  caused  by  the 
application  of  stimuli  to  the  nerves,  and  the  changes  in  the  amount 
of  the  sensations  are  dependent  upon  changes  in  the  intensity  of 
the  stimuli  which  occasion  them.  These  stimuli  admit  of  changes 
in  quantity,  which,  theoretically  at  least,  are  measurable  objectively, 
with  more  or  less  exactness.  Resulting  changes  in  consciousness 
can  only  be  measured  by  attentive  judgment,  which  directly  dis- 
criminates the  sensations  as  varying  in  intensity,  and  as  being 
greater  or  less,  one  than  the  other,  in  the  scale  of  impressions 
which  experience  has  framed. 

The  problems  of  the  measurement  of  sensation  may  then  be 
stated  as  follows  :  (1)  To  determine  how  little  and  how  much  of  each 
kind  of  stimulus  will  produce  respectively  the  least  and  the 
greatest  quantity  of  each  kind  of  sensation  of  which  the  mind  is 
capable,  or  to  find  the  quantitative  limits  within  which  sensations  of 
each  sense  are  possible  ;  and  (2)  to  determine  the  law  of  the  relation 
under  which  changes  in  the  intensity  of  sensations,  as  estimated 
in  consciousness,  are  dependent  upon  changes  in  the  intensity  of 
the  stimuli. 

§  5.  Unexpected  and  insuperable  difficulties,  however,  stand  in 


360  MEASUREMENT   OF   SENSATIOJ^S. 

the  -way  of  a  direct  solution  of  either  of  the  two  above-mentioned 
problems,  even  in  the  modified  form  in  which  they  were  last  stated. 
For,  in  the  first  place,  it  is  only  with  respect  to  sensations  of  press- 
ure and  of  the  muscular  sense  that  we  can  measure  objectively  the 
physical  energies  which  act  on  the  nervous  end-organs,  with  much 
approach  to  perfect  exactness.'  The  amplitude  of  the  acoustic  waves 
in  the  air  which  originate  from  a  given  source  would  indeed  admit 
of  exact  measurement  ;  but  the  modifications  which  these  waves 
undergo  before  they  reach  the  nerve-cells  and  nerve-fibres  of  the 
inner  ear  are  so  complicated  as  to  make  it  impossible  to  calculate 
accurately  the  amount  of  the  physical  stimulus  which  is  directly 
applied  to  the  end-organs  of  healing.  The  photo-chemical  and 
thermic  effects  of  light  may  be  measured  objectively.  But  this 
light  is  not  the  direct  physical  stimulus  for  the  fibres  of  the  oj)tic 
nerve,  or  even  for  the  end-organs  of  the  retina ;  and  we  have  no 
sufficient  means  for  estimating  the  amount  of  those  chemical  changes 
in  the  visual  substances,  or  pigments  of  the  eye,  which  are  supposed 
to  be  the  immediate  excitants  of  the  terminal  apparatus  of  vision. 
The  case  is  yet  more  hopeless  with  respect  to  the  senses  of  taste 
and  smell ;  inasmuch  as  we  do  not  even  know  what  pi'operties  smell- 
able  and  tastable  substances  must  possess  in  order  to  influence  the 
nerves  of  those  senses.  The  objective  measurement  of  the  stimulus 
for  sensations  of  temperature  also  is  made  difficult  by  the  fact  that 
its  amount  is  dependent  upon  the  zero-point  of  the  skin  itself, 
since  this  point  is  different  at  different  times  and  for  different 
areas  of  the  entire  surface,  and  is  always  difficult  of  precise  deter- 
mination. 

Moreover,  could  we  measure  with  perfect  exactness  the  intensity 
of  the  stimulus  as  it  is  applied  directly  to  the  appropriate  end- 
organs  of  sense,  our  knowledge  of  the  intensity  of  the  necessary 
physical  antecedents  of  the  resulting  sensations  would  be  far 
enough  from  complete.  How  do  the  end-organs  modify  the  quan- 
tities of  the  stimuli  before  they  transmit  their  effect  to  the  conduct- 
ing nerve-fibres  ?  Precisely  how  much  further  modffication  do 
these  quantities  receive  in  transmission  to  the  central  organs,  at 
the  hands  of  the  conducting  nerve-tracts  ?  What  are  the  laws  which 
control  the  reception,  diffusion,  and  modification  of  the  different 
intensities  of  the  transmitted  nerve-commotions,  within  those  parts 
of  the  nervous  mechanism  (the  central  organs),  where  they  become 
the  immediate  occasions  of  the  rise  and  change  of  sensations  in  the 
mind  ?  These  are  questions  to  which  we  are  absolutely  unable  to 
give  any  satisfactory  answer. 

'  Comp.  Wuudt,  Philosopliische  Studien,  1883,  II.,  hefti.,  pp.  10 ff. 


LEAST   OBSERVABLE  DIFFERElSrCE.  361 

§  6.  But  if  an  exact  objective  measurement  of  the  physical  stim- 
uli is  intrinsically  difficult,  an  exact  subjective  measurement  of  the 
sensations  themselves  is  inherently  impossible.  Such  subjective 
measurement  can  exist  at  all  only  in  the  form  of  a  judgment  which 
compares  two  or  more  sensations  with  a  view  to  pronounce  whether 
they  are  equal  in  intensity  ;  or,  if  unequal,  which  is  the  greater  and 
which  the  less  of  the  two.  But  we  have  seen  that  the  ordinary 
estimate  of  the  absolute  strength  of  a  sensation  is  able  simply  to 
assign  to  it  an  indefinite  position  in  the  scale  of  its  kind.  With 
certain  exceptions,  scientific  analysis  can  do  little  to  exclude  the 
uncertainties  of  the  ordinary  estimate.  These  exceptions  are  all  of 
the  following  kind  :  Where  two  sensations  of  the  same  quality  are 
produced,  either  simultaneously  on  difierent  corresponding  areas  of 
the  same  organ  or  successively  (with  the  most  favorable  interval  be- 
tween) upon  the  same  area,  by  amounts  of  stimulation  that  are  very 
nearly  or  precisely  equal,  the  attentive  mind  can  discriminate  the 
minute  differences,  or  exact  equality,  of  the  intensities  of  these  two 
sensations,  with  a  great  degree  of  nicety.  The  problem  of  meas- 
uring the  quantity  of  sensations  depends,  therefore,  upon  obtaining 
the  least  observable  differences  in  intensity  for  each  kind  of  sensa- 
tions, and  for  every  point  along  the  scale  of  degrees  of  intensity. 

But  in  this  connection  another  occasion  for  doubt  and  debate 
arises.  Is  "the  least  observable  difference"  of  two  sensations  it- 
self a  constant  quantity  ?  The  affirmative  answer  to  this  question 
is  assumed  by  Fechner  '  and  all  strenuous  advocates  of  the  law 
which  he  defends.  It  has  even  been  argued  that  to  hold  another 
than  the  affirmative  view  involves  a  contradiction  in  terms."  What 
can  be  meant,  it  is  asked,  by  a  "least  obsei'vable  difference  "  in  in- 
tensity between  two  sensations,  unless  it  be  that  this  difference  is 
a  constant  unit  for  the  measurement  of  those  sensations  of  the 
same  kind  which  lie  near  the  same  point  in  the  scale  ?  If  the  dif- 
ference is  more  than  just  observable,  then  of  course  it  is  not  the 
least  observable  ;  if  it  is  less,  then  it  is  not  observable  at  all — that 
is  to  say,  there  is  no  change  in  sensation.  But  to  this  argument 
the  following  reply  is  pertinent :  The  "least  observable  difference  " 
is  not  itself  a  mental  entity  or  a  mental  state,  that  can  be  measured 
and  used  as  a  unit  for  measuring  the  quantity  of  other  mental 
states.  For  example,  if  the  addition  of  n  to  the  stimulus  *S^  is  the 
smallest  amount  that  will  produce  such  a  change  in  the  mental 
state  X  as  to  cause  it  to  pass  over  into  x\  which  the  mind  recog- 

'  Elemente  d.  Psychophysik  (1860\  i.,  p.  54  f. ;  In  Sachen  d.  Psychophysik 
(1877\  p.  45  f. ;  Revision  d.  Hanptpunkte  d.  Psychophysik  (1882),  p.  18  f. 
■  Comp.  the  first  edition  of  Wundt's  Physiolog.  Psychologie,  p.  294. 


362  MEASUEEMENT   OF   SENSATION'S. 

nizes  as  having  a  greater  quantity  of  sensation  than  x,  such  fact  is 
to  be  stated  and  accepted  as  a  mere  fact ;  it  does  not  follow,  how- 
ever, that  we  may  conclude  that  x'  —  x  =  A,  and  that  this  A  is  en- 
titled to  a  name  ("  least  observable  difference  ")  and  a  rank  among 
the  mind's  experiences  by  way  of  sensation.  There  are  no  seiisa- 
tl07^s  (whatever  physical  occasions  of  sensations  may  exist)  except 
those  that  appear  in  consciousness  ;  ex  hypothesi,  there  appear  in 
consciousness  only  x  and  x',  and  no  sensation  whatever  Ijing  be- 
tween the  two  in  intensity.  We  judge,  indeed,  that  the  intensity 
of  x',  now  present  in  experience,  is  greater  than  was  the  intensity  of 
X,  now  remembered  as  an  image  of  past  experience ;  but  A  (or  x'  —  x) 
is  a  mere  abstraction,  a  figment  of  the  experimenter's  brain,  and  not 
a  real  experience  of  the  person  with  whom  he  is  experimenting. 

Moi'eover,  if  A  were  capable  in  any  case  of  being  regarded  as  a 
unit  of  subjective  measurement,  it  would  by  no  means  follow  that 
its  mental  value  is  a  constant.  That  n,  or  the  amount  of  stimulus 
which  must  be  added  to  S  in  order  to  produce  an  observable  change 
in  the  quantity  of  sensation,  is  not  constant  we  know  beyond  doubt. 
For  the  different  senses,  for  different  individuals,  for  different  de- 
grees of  the  absolute  stimulus  {i.e.,  value  of  S),  for  different  con- 
ditions of  the  organs  of  sense,  this  amount  n  is  constantly  varying. 
The  amount  of  A  may  also  be  held  to  vary,  according  to  psycho- 
logical changes  in  the  means  and  power  of  mental  discrimination, 
such  as  we  have  no  way  of  measuring  objectively.  For  we  must 
again  insist  upon  the  fact  that  the  real  quantity  of  a  sensation  is 
not  the  same  thing  as  the  estimated  quantity  of  the  same  sensation. 
The  "  least  observable  difference  "  would  not,  therefore,  necessarily 
be  the  same  as  the  least  real  difference,  between  two  sensations.' 
It  is  not  the  mind's  custom  to  attend  accurately  to  the  changes  in 
quantity  of  its  sensations  as  such.  Properly  speaking,  many  con- 
siderable changes  in  our  sensations,  as  we  may  judge  by  the  guid- 
ance they  give  to  the  bodily  motions  and  the  mental  train,  do  not 
appear  in  consciousness  with  a  label  of  exact  quantitative  measiire- 
ment,  as  it  were,  attached  to  them. 

It  is  therefore  obvious,  from  the  great  difficulties  which  belong 
inseparably  both  to  the  objective  measurement  of  the  stimuli  of 
sensation,  and  to  the  subjective  measurement  of  the  resulting  sen- 
sations, that  any  law  of  their  relation  can  have  only  an  indefinite 
statement  and  a  secondary  value. 

§  7.  Two  methods  of  determining  the  lower  limit,  or  minimum 
of  stimulus  producing  a  sensation,  are  possible.  In  the  use  of  one 
method,  a  weak  stimulus,  but  somewhat  above  the  amount  needed 
'  Comp.  Stumpf,  Tonpsychologie,  I.,  p.  51  f. 


DETERMINING  THE  LIMIT.  363 

to  produce  a  sensation  is  applied  ;  its  intensity  is  then  diminished 
by  minute  gradations  until  the  exact  point  is  readied  and  noted  at 
■which  it  ceases  to  produce  any  sensation  at  all.  In  the  use  of  the 
other  method  a  stimulus  too  weak  to  produce  any  sensation  is  first 
applied ;  its  intensity  is  then  very  gradually  increased  until  it 
begins  to  produce  the  smallest  observable  sensation.  Both  ways 
may  be  combined,  and  thus  the  "  sensitiveness  "  of  each  organ  of 
sense,  and  of  each  part  of  each  organ,  may  be  determined.  Such 
sensitiveness  increases,  of  course,  in  inverse  ratio  to  the  amount  of 
stimulus  necessary  for  producing  any  sensation  at  all,  or  for  pro- 
ducing a  sensation  estimated  as  having  a  definite  degree  of  energy. 
The  effort  to  determine  the  lower  limit  of  sensations  of  sight  and  of 
sound  is  embarrassed  by  the  facts  that  the  retina  is  always  under 
excitation  from  the  chemical  changes  going  on  in  its  pigments,  and 
therefore  has  a  certain  quantum  of  so-called  "  light  of  its  own," 
and  that  such  a  thing  as  "  absolute  stillness  "  cannot  probably  be 
secured  for  the  ear.  Total  absence  of  sensation  in  the  ear,  could 
it  be  secured,  would  not  be  comparable  to  the  black  which  we  see 
with  the  eyes  closed.' 

The  upper  limit,  or  maximum  amount  of  stimulus  which  the  ner- 
vous organism  can  receive,  cannot  be  determined  experimentally. 
The  use  of  excessive  quantities  of  stimulus  is  not  only  too  fatigu- 
ing but  also  too  dangerous  to  the  structure  of  this  organism  (for 
example,  of  blinding  light  upon  the  eye,  stunning  noise  in  the  ear, 
etc.)  to  admit  of  successful  experiment  in  this  dii-ection.  Moreover, 
the  application  calls  out  so  much  of  those  varied  forms  of  feeling 
which  are  allied  with  all  the  specific  sensations  as  to  overwhelm 
the  latter  with  the  former.  Very  concentrated,  sour,  or  bitter  solu- 
tions, or  very  intense  odors,  are  not  simply  tasted  and  smelled ;  they 
are  oho  felt  with  aU  the  adjoining  parts  of  the  body.  Very  strong- 
light  and  very  loud  noise  do  not  simply  heighten  the  specific  sensa- 
tions of  sight  and  hearing,  they  rather  destroy  them  in  a  flood  of  pain- 
ful feeUng.  We  may  affirm  in  general,  however,  that  the  "  capacity  " 
of  each  sense  varies  directly  as  the  amount  of  stimulus  which  it  can 
receive.     The  "  circuit "  or  range  of  the  sensations  of  each  sense 

C  1 

may  then  be  said  to  be  —  where  _  stands  for  the  measure  of  the 

sensitiveness,  and  C  for  the  measure  of  the  capacity,  of  each  sense." 

^  On  the  question  whether  absolute  stillness  is  possible,  and  whether  the  ear 
has  any  sensation  comparable  to  the  black  of  the  eye,  see  Lotze,  Medicinische 
Psychologie,  p.  218 ;  Volkmauu  von  Volkmar,  Lehrbuch  d.  Psychologie, 
1884,  I.,  p.  273  ;  and  Stumpf,  Tonpsychologie,  I.,  p.  380  f. 

2  See  Wundt,  Physiol og.  Psychologie,  i. ,  p.  324. 


364  MEASUEEMENT   OF   SENSATIOl^TS. 

§  8.  There  are  tliree  methods  of  determining  experimentally  tke 
least  observable  differences  in  sensations.  These  are  called,  (1)  the 
method  of  least  observable  difference  ;  (2)  the  method  of  average 
errors  ;  (3)  the  method  of  correct  and  mistaken  cases.  Of  the 
three  methods,  the  first  bears  the  name  which  suggests  the  real 
subject  of  investigation  in  them  all.  This  method  is  divided  by 
Wundt '  and  others  into  two — namely,  the  method  of  mean  grada- 
tions of  sensation,  and  the  method  of  minimum  changes  of  sensation. 
Bat  these  are  really  only  two  modes  of  applying  one  method.  In  the 
one  case  an  attempt  is  made  to  form  a  scale  of  stimuli  whose  intervals 
correspond  to  equally  large  intervals  in  our  estimate  of  the  resulting 
sensations,  by  judging  what  amount  of  the  stimulus  produces  a  sensa- 
tion (M)  that  lies  exactly  midway  between  two  other  sensations  (A  and 
O)  separated  by  a  clearly  perceptible  interval  (hence  A :  M  : :  M  :  0). 
Between  A  and  M  another  middle  terra,  the  sensation  of  magnitude  K, 
may  then  be  sought  and  found  ;  and  so  on  until  the  limit  of  observ- 
able differences  is  reached.  This  mode  is,  however,  less  comprehen- 
sive and  fruitful  than  the  second  mode  of  applying  the  same  principle. 
The  "  method  of  minimum  changes  in  sensation  "  seeks  directly  to 
establish,  all  along  the  scale  of  intensities  of  the  stimuli,  that  change 
in  their  strength  which  is  just  enough  (and  no  more  than  enough) 
to  produce  a  minimum  change  in  sensation.  Such  minimum 
change  may  be  conceived  of  as  standing  just  on  the  ''threshold" 
of  our  power  to  make  distinctions  in  the  degrees  of  strength  with 
which  our  sensations  are  apprehended  in  consciousness.^ 

The  "  method  of  average  errors"  (2)  begins  by  fixing  upon  some 
given  sensation  which  is  known  to  bo  caused  by  a  given  intensity 
of  stimulus  ;  the  attempt  is  then  made  also  to  fix  upon  another 
stimulus,  by  means  of  the  sensation  it  produces,  as  being  exactly 
equal  to  the  former.  The  trial  results  in  a  number  of  guesses  that 
are  more  or  less  out  of  the  way.  By  averaging  all  the  cases  of  trial, 
the  degree  of  sensitiveness  to  distinctions  is  discovered.  In  other 
words,  the  method  attempts  to  determine,  at  each  point  along  the 
scale  and  for  each  kind  of  stimulus,  the  differences  in  the  strength 
of  stimuli  that  are  just  below  the  amount  necessary  to  make  an  ob- 
servable difference  in  the  resulting  sensations. 

In  the  "  method  of  correct  and  mistaken  cases  "  (3)  minute  ad- 
ditions or  subtractions  of  the  amount  of  stimulus  are  made,  with 
the  intent  of  seeing  how  many  cases  of  right  and  how  many  of 

'  See  Wundt  Pliysiolog.  rsycliologie.  i. ,  p.  325  f.,  and  comp.  his  Philosoph- 
ische  Studien,  1881,  p.  8  f. 

-Called  "Unterschiedsschwelle"  by  Fechuer,  Elemented.  Psychophysik, 
i.,p.  242. 


CORRECT   AND   MISTAKEN   GUESSES.  365 

wrong  guessing,  respectively,  will  result  for  each  of  the  different 
positions  in  the  scale  of  the  stimuli,  and  for  each  kind  of  stimulus. 
If,  then,  the  proportion  of  the  number  of  correct  to  mistaken  guesses 
is  kept  the  same  for  all  points  of  the  scale,  the  amount  of  change 
in  the  stimulus  necessary  for  this  may  be  held  to  measure  the  sen- 
sitiveness to  differences  which  belongs  to  each  of  these  points. 
Thus,  let  n  =  the  whole  number  of  guesses,  and  r  —  the  number 

/' 
of  right  guesses  ;  then  —  =  the  sensitiveness  to  differences.     But 
?i 

the  positive  value  of  this  quotient  being  kept  unchanged,  the 
amount  of  stimulus  added  to  or  subtracted  from  the  original 
amount  will  measure  the  sensitiveness  to  differences  for  all  points  of 
the  scale.  Tiiis  method  has  been  largely  used  and  warmly  defended 
by  Fechner '  in  experimenting  with  sensations  of  pressure.  Much 
doubt  has,  however,  been  thrown  upon  the  use  made  of  it  by  this 
observer ;  and  especiall}''  upon  the  propriety  of  reckoning  the  doubt- 
ful cases  one-half  to  the  right  and  one-half  to  the  wrong  guesses.^ 

A  comparison  of  the  above-mentioned  methods  shows  that  they 
ai'e  all  simply  different  ways  of  measuring  the  sensitiveness  of  the 
mind  to  minute  differences  in  the  quantity  of  its  sensations  as  de- 
pendent upon  changes  in  the  intensity  of  the  stimuli.  They  should 
never  be  employed,  therefore,  without  taking  into  account  the 
fact  that  various  other  causes,  besides  such  objective  changes  in 
the  stimuli,  always  co-operate  to  determine  the  degree  of  this 
mental  sensitiveness.  To  eliminate  these  other  factors  from  the 
calculation  is  by  no  means  easy. 

§  9.  The  one  law  which  claims  to  be  a  scientific  expression  of  the 
relations  between  changes  in  the  intensity  of  stimuli  and  changes 
in  the  quantity  of  the  resulting  sensations  is  that  known  by  the 
name  of  E.  H.  Weber.  This  observer  originally  used  the  method 
of  least  observable  differences  as  applied  to  sensations  of  pressure 
and  to  the  measurement  of  lines  by  the  eye.'  "  Weber's  law  "  has 
been  elaborated,  confirmed  by  a  vast  amount  of  espei"iment,  and 
defended  as  a  psycho-physical  pi'inciple  of  the  widest  application, 
by  Fechner  (in  the  works  referred  to,  note,  p.  361).  The  significant 
addition  which'  Fechner  has  made  to  Weber's  law  consists  in  the 
assumption  that  all  just  observable  differences  are  equally  great. ^ 

'  Elemente  d.  Psychophysik,  i.,  pp.  98-120. 

"  On  this  point  see,  especially,  G.  E.  Miiller,  Grundlegung  d.  Psychophy- 
sik, p.  36  f.  ;  and  Wundt,  Physiolog.  Psychologie,  i. ,  p.  330  f. 

^  Especially  in  articles  on  the  sense  of  toiich,  in  R.  Wagner's  Handworterb. 
d.  Physiologie,  III.,  ii.  ;  and  Archiv.  f.  Anat,  Physiol.,  etc.,  1835,  pp.  153  ff. 

*  On  this  point  comp.  Funke,  in  Hermann's  Handb.  d.  Physiol. ,  III. ,  ii. ,  p. 
349  f. ;  and  Wundt,  Philosophische  Studien,  II.,  Ileft  1,  p.  G  f. 


366  THE   LAW   OF   WEBEE. 

It  is  therefore  also  called  "  Fechner's  law."  As  an  empirical  law 
it  attemjDts  to  put  into  scientific  form,  on  the  basis  of  experimen- 
tal investigation,  the  truth  of  ordinary  experience — namely,  our 
estimate  of  the  difference  in  amount  between  two  sensations  is 
not  directly  proportioned  to  the  real  difference  in  their  stimuli, 
but  the  latter  must  increase  faster  than  does  the  former.  For  ex- 
ample, the  difference  in  the  intensity  of  the  shadows  cast  by  one 
and  by  two  wax  tapers  is  very  perceptible  in  a  dimly  lighted  room, 
but  is  altogether  unobservable  in  open  sunlight ;  or  the  strength 
with  which  two  clocks  tick  can  be  discriminated  with  much  nicety, 
but  not  the  amount  of  noise  made  by  two  successive  discharges  of  a 
cannon. 

In  other  words,  if  we  assume  that  the  least  observable  difference 
in  sensations  may  be  regarded  as  a  constant  quantity,  then,  in 
order  to  produce  this  increase  or  decrease  in  the  amount  of  sen- 
sation, the  addition  or  subtraction  of  a  much  greater  amount  of 
stimulus  is  needed  for  the  higher  than  for  the  lower  portions  of  the 
scale.  Weber's  law  undertakes  to  tell  us  how  much  greater  such 
required  amount  of  stimiilus  must  be.  It  admits  of  statement  in 
the  several  following  ways  :  The  difference  between  any  two  stimuli 
is  experienced  as  of  equal  magnitude  in  case  the  mathematical  re- 
lation of  those  stimuli  remains  unaltered  ;  or,  If  the  intensity  of 
the  sensations  is  to  increase  by  equal  absolute  magnitudes,  then 
the  relative  increase  of  the  stimulus  must  remain  constant ;  or.  The 
strength  of  the  stimulus  must  ascend  in  a  geometrical  proportion 
in  case  the  strength  of  the  sensation  is  to  increase  in  an  arith- 
metical proportion.* 

1  See  Wundt,  Physiolog.  Psychologie,  i.,  p.  335.  For  the  detailed  mathe- 
matical discussion  and  expression  of  Weber's  law  the  reader  is  referred  to 
the  technical  works,  especially  of  Fechner  and  G.  E.  Miiller.  A  simple  state- 
ment of  Weber's  principle  may  be  given  as  follows  :  Let  H=  the  intensity  of 
the  light  of  one-half  of  a  white  field  ;  j-^  =  the  smallest  fraction  of  stimulus 
added  to  H  that  will  produce  an  observable  increase  in  this  intensity ;  and 
JET  H — ~  =  the  intensity  of  the  other  half  of  the  same  field.  Then  let  8  = 
the  sensation  produced  by  II;  S  +  s  =  the  sensation  produced  by  11+  77777. 
and  s  will,  of  course,  represent  the  so-called  least  observable  difference  at  this 
point  in  the  scale.  We  have,  then,  H  produces  S;  H  +  77577,  or  |{ji  ZT,  pro- 
duces S  +  s;  lolf  £[+  LP."  ^  ,  or  igi-ISr)  H,  produces  8  +  s  +s;  and  so  on. 
That  is  to  say,  if  s  is  to  be  kept  of  the  same  magnitude,  then  i/must  be  mul- 
tiplied by  the  same  magnitude  {{f,}-,)- 

The  three  fundamental  formulas  which  Fechner  has  employed  to  state  and 
demonstrate  the  law  are  the  following  :  Let  8  be  the  magnitude  of  the  sensa- 
tion caused  by  the  stimulus  2,  and  AS  a  just  observable  increase  in  this  sen- 


'QUANTITY   OF   TACTUAL   SENSATIONS.  367 

The  empirical  data  upon  which  the  advocates  of  Weber's  law  rely 
are  very  numerous,  but  their  value  and  trustworthiness  are  often 
much  diminished  by  the  fact  that  most  experimenters  have  failed 
to  isolate  sufficiently  the  exact  problem  which  it  was  desired  to 
solve.  Nevertheless,  the  data  show  that  the  law  summarizes  many 
facts  reasonably  well  within  a  certain  range  of  sensations  lying  near 
the  middle  of  the  scale  of  quantity.  Near  both  the  upper  and  the 
lower  limits  the  law  fails  to  prove  applicable  ;  even  in  the  regions 
and  under  the  circumstances  which  are  most  favorable  it  is  only 
approximately  true.  Many  fluctuations  of  unknown  significance 
and  origin  occur  in  all  the  senses. 

§  10.  In  determining  the  least  observable  sensations  of  touch, 
the  result  is  largely  dependent  upon  the  presence  of  muscular  sen- 
sations also.  It  further  depends  upon  the  method  in  which  the 
comparison  is  made  ;  for,  as  Weber  discovered,  an  actually  present 
sensation  can  be  compared  with  the  remembered  image  of  one  just 
past  better  than  two  present  sensations  can  be  compared.  The  in- 
terval of  time  and  the  locality  of  the  organ  have  also  a  great  influ- 
ence. Most  persons  observe  a  stronger  sensation  of  pressure  when 
the  weight  is  laid  on  the  left  than  when  it  is  laid  on  the  symmetri- 
cal place  of  the  right  side.  The  same  amount  of  surface  must  be 
covered,  and  the  objects  compared  must  have  the  same  temperature, 
in  order  to  secure  trustworthy  results  of  experiment.  Weber 
found  that,  when  the  interval  was  fifteen  to  thirty  seconds,  under 
the  most  favorable  circumstances,  14|-  could  be  distinguished  from 
15  grammes,  or  14^  from  15  ounces.  That  is,  some  persons  can 
distinguish  weights  which  differ  as  29  :  30,  by  the  sensations  of 
pressure  they  occasion,  when  laid  on  the  volar  side  of  the  last 
phalanges.  By  raising  the  weights  the  nicety  of  discrimination  can 
be  increased  so  as  to  be  represented  by  the  proportion  39  :  40. 

sation  wliicli  is  caused  by  an  increase  of  the  stimulus  =  A2.  Let  (7  be  a  con- 
slant  dependent  on  tbe  values  chosen  for  ;!?  and  2.  Then  AiS  =  -^.  Let  it 
be  further  assumed  that  A/S  remains  constant  whatever  valiies  for  8  and  A2 
are  assumed;  then  dS  =  0 -^,  and  by  integration  S=C  log.  2,  which  is 
Fechner's  "fundamental  formula."  But  if  the  stimulus  is  just  belotcthe  least 
observable  amount,  and  be  =  2%  then  substituting  in  the  above  formula  we 
have  0  =  C  log.  2' ;  from  which  Fechner  derives  formula  No.  2  (the  formula 

of  measurement),  namely,  8  =^  C  log.  — ,  which  means  that  the  magnitude  of 

the  sensation  is  "  negative,^''  in  case  the  stimulus  sinks  below  the  least  observ- 
able =  2'.  If  two  sensations  {8  and  8)  are  observably  different,  then  6'  —  8' 
=  C  (log.  2—  log.  2') ;  this  is  called  the  "formula  of  difference,"  and  means 
that  the  difference  in  the  intensity  of  two  sensations  is  proportional  to  the 
logarithm  of  the  quotient  of  the  magnitudes  of  their  stimuli. 


368  THE   LAW   OF   WEBER. 

By  an  extended  series  of  experiments  with  weights  ranging  from 
300  to  3,000  grammes  Fechner  '  emploj^ed  the  method  of  correct 
and  mistaken  cases  to  confirm  Weber's  law  as  applied  to  combined 
sensations  of  pressure  and  of  the  muscular  sense.  Some  experi- 
ments were  made  with  both  hands  ;  others  with  the  right  or  left 
separately.  The  weight  used  to  add  or  subtract  was  either  0.04  or 
0.08  of  the  absolute  weight.  The  results  showed  that  the  law  held 
only  approximately  for  all  the  series  of  experiments,  and  not  abso- 
lutely for  any  one  series.  As  calculated  by  G.  E.  Miiller  °  they 
give,  instead  of  a  constant  quotient  to  express  the  degree  of  sensi- 
tiveness (as  Weber's  law  requires),  a  quotient  varying  from  ^j-^vg-  for 
•weights  of  300  grammes  to  ^^  for  weights  of  3,000  grammes.  Nor 
can  Fechner's  effort  to  correct  the  variation,  by  introducing  after- 
ward a  conjectural  allowance  for  the  weight  of  the  arm  itself,  be 
considered  successful.^  Biedermann  and  Lowit,  by  the  method  of 
just  observable  differences,  obtained  results  departing  widely  from 
Weber's  law.*  By  experimenting  with  weights  varying  from  10  to 
500  grammes  they  found  that  the  sensitiveness  to  pressure  rose 
with  the  increase  of  the  weights  from  10  to  400  grammes,  and  then 
fell  off  rapidly,  as  the  following  table  will  show  : 

Quotient  of  sensitiveness. 


.1. 

2.9 
-4^ 

The  trustworthiness  of  these  results  is  impaired,  however,  by  the 
fact  that  no  method,  except  the  doubtful  one  of  directing  "atten- 
tion "  exclusively  to  the  sensations  of  pressure,  was  employed  to 
exclude  the  disturbing  effect  of  the  muscular  sensations.  The 
same  observers  concluded,  also,  that  the  fineness  of  the  muscular 
sense,  when  isolated,  does  not  vary  according  to  Weber's  law.  They 
fixed  it  at  ^\  for  weights  of  250  grammes,  j{j  for  weights  of  2,500 
grammes,  -^^  for  weights  of  2,750  grammes. 

That  Weber's  law  does  not  hold  good,  near  the  lower  limits,  for 

1  Elemente  d.  Psjcliopliysik,  i,,  p.  183  f. 

^  Zixr  Grundlegung  d.  Psychopliysik,  p.  197. 

^  In  Sauhen  d.  Psychopliysik,  p.  198. 

*  See  Heriiig,  Sitzgsber.  d.  Wiener  Acad.,  LXXIL,  Abth.  iii.,  p.  343  f. 


solute  weight. 

Least  observable  diflference. 

Grammes. 

Grammes. 

10 

0.7 

50 

1.7 

100 

2.4 

200 

3.6 

300 

46 

400 

5.2 

450 

6.5 

500 

25.5 

QUANTITY    OF   TEMPERATURE-SEISrSATIOlSrS.  369 

sensations  of  pressure,  and  of  muscular  innervation  and  movement, 
is  admitted  by  all.  The  absolute  sensitiveness  of  these  sensations 
differs  greatly,  as  has  been  shown  (p.  346  f.),  for  different  localities 
on  the  surface  of  the  body.  Aubert  and  Kammler  found  the  light- 
est weight  which  produced  a  sensation  of  touch  to  be  0.002  gramme 
on  the  forehead,  temples,  and  dorsal  side  of  the  forearm  and  hands  ; 
0.003  gramme  for  the  volar  side  of  the  forearm  ;  0.005  gramme 
for  the  nose,  lips,  chin,  eyelids,  and  skin  of  abdomen  ;  0.005-0.015 
gramme  for  the  volar  side  of  the  fingers  ;  and  1  gramme  for  the 
fingernails  and  skin  of  the  heel.  This  kind  of  sensitiveness  has 
been  thought  to  be  chiefly  dependent  upon  the  number  of  the 
nervous  elements  present  in  the  skin,  its  thickness,  the  character 
of  its  tension  over  the  underlying  parts,  etc.  ;  but  its  variations  are 
by  no  means  parallel  with  those  of  the  sharpness  of  the  sense  of 
locality.  The  foregoing  and  similar  conclusions  all  need  to  be  re- 
vised in  the  light  of  Goldscheider's  determinations  of  the  pressure- 
spots. 

§  11.  Extraordinary  difficulties  accompany  the  attempt  to  apply 
Weber's  law  to  sensations  of  temperature.  As  has  alread}^  been  seen 
(p.  350  f.),  we  do  not  know  exactly  what  to  measure — whether  the 
rising  and  falling  of  the  thermic  apparatus,  or  its  actual  tempera- 
ture in  relation  to  its  own  zero-point ' — as  constituting  the  quanti- 
tative changes  in  the  stimuli.  Even  Fechner  admits  that  Weber's 
law  does  not  apply  to  the  sensitiveness  of  the  hand  to  changes  in 
temperature  when  it  is  itself  cooling  off;  but  he  thinks  the  law 
holds  good  approximately  for  degrees  of  warmth  varying  between 
25°  and  37.5°  C.  (77°-99.5°  Fahr.),  if  18.71°  C.  (65.66°  Fahr.)  be 
taken  as  the  zero-point.  The  assumption  of  this  zero-point  is, 
however,  arbitrary.  No  general  rule  for  the  quantity  of  sensations 
of  temperature  can  well  be  given  except  this  :  the  akin  is  most 
sensitive  to  changes  which  lie  near  its  oion  zero-point.  In  compar- 
ing two  temperatures  it  is  most  favorable  to  nice  discrimination 
that  one  should  lie  slightly  above,  the  other  slightly  below,  this 
point.  The  degrees  of  the  thermometer  between  which  the  maxi- 
mum of  sensitiveness  is  attainable  are  given  differently  by  differ- 
ent observers:  By  Nothnagel,  27^-33°  C.  (80.6°-91.4°  Fahr.) ;  by 
Lindemann,  26°-39°  C;  by  Alsberg,  35°-39°  C;  by  Fechner,  12°- 
25°  C. — where  it  is  so  great  as  not  to  be  easily  measurable  by  a 
good  quicksilver  thermometer  (about  \°  Fahr.).  Cold  and  heat  alike, 
when  applied  for  some  time,  reduce  greatly  the  sensitiveness  of 
the  skin  to  minute  changes  of  temperature  ;  by  heat  it  can  be  so 
dulled  as  not  to  distinguish  alterations  of  less  than  ^°  or  f°  Fahr.; 
'  So  Heriug,  see  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  430. 
24 


370  THE   LAW    OF   WEBER. 

bj  cold  it  can  be  rendered  insensible  to  changes  measuring  from 
2^  to  5i-=. 

We  have  already  seen  (comp.  p.  348  f.)  that  the  sense  of  tempera- 
ture depends  for  its  fineness  upon  the  extent  and  locality  of  the  sur- 
face excited.  Weber  found  that  water  at  29^-°  E.,  in  which  the 
Avhole  hand  was  immersed,  seemed  warmer  than  that  at  32^  R.,  to  a 
single  finger.  Nothnagel  placed  the  following  values  upon  the  fine- 
ness of  discrimination,  for  minute  variations  in  temperature,  of  dif- 
ferent parts  of  the  body  :  Middle  breast,  0.6°  C;  sides  of  the  same, 
0.4°;  middle  of  the  back,  1.2°;  sides  of  the  same,  0.9°;  hollow  of  the 
hand,  0.5°-0.4°;  back  of  the  same,  0.3°;  partsof  upper  and  lower  arm, 
0.2°;  cheeks,  0.4°-0.2°;  temples,  0.4°-0.3°.  More  recent  investiga- 
tions have  shown  that  the  table  of  sensitiveness  for  the  different  parts 
of  the  body  must  take  account  of  the  division  of  the  tempei'ature- 
sense  into  two  species,  and  of  the  locality  of  the  heat-spots  and 
cold-spots  in  all  such  different  parts.  On  the  basis  of  experiment 
with  areas  of  the  skin  whose  topography  with  respect  to  the  tem- 
perature-sense had  previously  been  investigated,  Goldscheider  has 
given  a  lengthy  statement  '  of  the  sensitiveness  of  different  parts 
of  the  body. 

Thus  he  finds  that  the  skin  of  the  head  is,  in  general,  little 
developed  for  the  sense  of  cold,  and  only  in  a  few  places  for  the 
sense  of  heat.  The  sensitiveness  of  the  forehead  to  cold  is  intense, 
but  to  heat  only  moderate  ;  that  of  the  breast  to  cold  moderate 
along  the  sternum,  and  elsewhere  very  intense,  while  to  heat  it  is 
only  moderate  except  near  the  uiiDj^les  ;  that  of  the  back  everywhere 
very  intense  to  cold,  and  only  moderate  to  heat ;  while  in  all  parts 
of  the  hand  the  intensity  of  sensitiveness  to  both  cold  and  heat 
is  alike. 

In  general,  the  skin  in  the  median  line  of  the  body  seems  much 
less  sensitive  to  changes  in  temperature  than  at  its  sides ;  and  the 
number  of  thermic  elements  (according  to  Goldscheider,  the  dis- 
tributory  fibrils  of  the  temperature-nerves),  the  thickness  of  the  skin, 
etc.,  are  determining  factors. 

§  12.  The  possibility  of  executing  or  appreciating  a  musical 
passage  in  which  the  intensity  of  the  successive  notes  is  brought 
to  a  certain  standard  of  memory,  or  in  which  these  notes  are  nicely 
shaded  so  as  to  constitute  a  crescendo  or  a  diminuendo,  ajDpears  to 
depend  upon  appljdng  to  sensations  of  sound  some  law  resembling 
that  of  Weber.  It  is  partly  by  comparing  such  sensations  with 
their  images  in  memory  that  the  singer  or  player  reproduces  certain 

'  See  the  Arcliiv  f.  Auat.  u.  Physiol.,  Physiolog.  Abth.,  1885,  Supplement- 
Band,  pp.  GO  If. 


MEASUREMENT   OF   SOUND.  371 

notes  previously  executed,  with  about  the  same  stress  of  tone.* 
Moreover,  in  order  to  shade  the  relative  intensities  of  successive 
tones,  our  appreciation  of  their  differences  needs  to  be  much  greater 
for  those  that  have  a  low  degree  of  intensity.  Many  obstacles, 
however,  stand  in  the  way  of  determining  either  the  lower  limit 
or  the  least  observable  difference  for  sensations  of  sound.  The 
general  dif3S.culty  which  belongs  to  investigating  the  intensity  of 
sensations,  even  under  the  most  favorable  circumstances,  is  here 
enhanced  by  the  facts,  that  the  pitch  and  timbre  of  each  clang  have 
much  to  do  with  our  judgment  of  its  strength  ;  that  different  ears 
differ  so  widely  in  their  organic  susceptibility,  while  the  mind  is 
peculiarly  sensitive  to  changes  of  feeling  and  judgment  connect- 
ed with  sensations  of  sound,  and  thus  very  weak  sensations  are 
vacillating  and  unsteady  in  consciousness,  and  sounds  appear  and 
disappear  in  the  ear  while  the  degree  of  stimulus  and  of  attention 
are  unchanged  ;  that  the  reflection  and  interference  of  the  acoustic 
nerves,  their  distance  and  direction,  and  the  absence  or  presence  of 
"  entotic  "  sounds,  are  so  influential ;  and,  finally,  that  it  is  impossi- 
ble to  discover  a  sounding  apparatus  of  definitely  ascertainable  and 
uniform  intensity  of  action. 

§  13.  None  of  the  means  employed  for  determining  the  amount 
of  stimulus  necessary  to  produce  the  weakest  sensations  of  sound, 
or  the  least  observable  differences  in  such  sensations,  are  entirely 
satisfactory.  The  method  of  listening  to  noises  made  by  falling 
weights  is  rendered  uncertain  by  the  fact  that  the  character,  both  of 
the  weight  an'd  of  the  surface  on  which  it  strikes,  has  so  much  in- 
fluence. Moreover,  it  is  a  matter  of  dispute  whether  the  intensity 
of  the  stimulus  is  to  be  measured  by  the  product  of  the  mass  into 
the  height  from  which  the  body  falls  (m  x  h)  or  into  the  square- 
root  of  that  height  (in  x  Vh).  It  is  possible  that  neither  of  these 
measurements  is  exact. ^  Assuming  the  former  to  be  correct  (noise 
=  m  X  h),  by  using  a  sound-pendulum  A.  W.  Volkmann  found  that 
differences  in  intensity  are  observable  when  they  stand  in  the  pro- 
portion 3 : 4.  Vierordt,  on  the  other  hand,  concluded  that  the  latter 
measurement  (noise  =.  m-^h)  is  more  nearly  correct;  and  by  assum- 
ing Vierordt's  view,  and  using  iron  balls  that  fell  vertically  on  a  vi- 
bx'ating  plate,  Norr  ^  attempted  to  fix  a  unit  of  measurement.  This 
unit  h&  made  =  1,500  milligramme-millimetres  vsdth  the  ear  distant 
50  ctm.  from  the  soiu'ce  of  the  sound.     Experimenting  with  sounds 

'  Comp.  Stumpf,  Tonpsychologie,  I.,  p.  345 f. 

''■  Comp.  Wundt,  Physiolog.  Psycliologie,  i.,  p.  341  and  note  ;  and  E.  Tiscber, 
in  Philosophische  Studien,  I.,  heft  4,  p.  543  f. 
-  Zeitschrift  f.  Biologic,  1879,  XV.,  p.  297  f. 


372  THE   LAW   OF   WEBER. 

ranging  in  intensity  from  those  a  little  above  the  least  observable  to 
those  of  unpleasant  strength  (1.71-524167.8  times  the  unit),  and 
dividing  the  entire  scale  into  7  groups,  w^ithin  each  of  which  about 
1,000  experiments  were  conducted,  he  found  that  the  proportion  of 

right  guesses  to  the  entire  number  made  (  —  )  remained  approxi- 
mately constant — that  is,  that  Weber's  law  holds  for  sounds  of  vary- 
ing iutensit}'.  A  large  allowance,  however,  had  to  be  made  for 
relations  of  time ;  the  percentage  of  correct  guesses  being  about  8.7 
larger  when  the  sound  of  greater  intensity  followed  that  of  less 
intensity. 

More  recently,  E.  Tischer  '  has  apjDarently  added  some  evidence 
to  the  validity  of  Weber's  law  by  experimenting  with  an  improved 
form  of  the  method  of  Vierordt  and  Norr.  Keeping  one  of  the  two 
sounds  to  be  compared  at  a  constant  intensity,  he  increased  or 
diminished  the  other  until  from  4  to  6  successive  correct  guesses 
as  to  their  relative  value  were  obtained.  But  the  fact  that,  when 
the  second  stimulus  was  diminished  until  certainty  of  judgment 
was  obtained,  very  considerable  unexplained  variations  from  the 
results  expected  by  Weber's  law  occurred  leaves  much  doubt  still 
hanging  over  the  matter.  In  order  to  harmonize  the  conflicting- 
results,  the  proposal  has  been  made  to  introduce  another  function 
into  the  formula,  noise  =  m  h  or  my/h.  All  the  investigations, 
therefore,  still  leave  the  question  of  the  applicability  of  Weber's 
law  to  sensations  of  sound  in  a  rather  uncertain  condition. 

Little  or  nothing  has  been  accomplished  by  expetiment  to  de- 
termine whether  the  same  law  applies  to  the  intensity  of  musical 
tones.  Among  the  various  factors  which  enter  into  our  judgment 
of  the  intensity  of  tones,  the  "  color-clang  "  is  especially  influential." 
Absolute  pitch  and  intervals  of  pitch  are  also  very  important.  In 
general,  tones  and  noises  of  a  higher  pitch,  with  an  equal  objective 
intensity  of  stimulus,  are  judged  to  be  louder  than  those  of  a  lower 
pitch.  Konig  showed  that  a  tuning-fork  of  the  pitch  c  must  have 
about  four  times  the  amplitude  of  vibration  required  by  one  of  the 
pitch  C,  in  order  to  produce  upon  the  ear  the  same  effect  from  the 
same  distance. 

§  14.  The  various  attempts  to  determine  the  lower  limit  of  sound 
for  the  human  ear  have  not  resulted  in  any  precise  statement. 
Schafhiiutl,  after  experiments  in  as  near  perfect  stillness  as  possi- 
ble, at  midnight,  fixed  the  limit  at  the  noise  made  by  a  cork  ball  of 
1  milUgrarame  weight  (about  0.0154  gr.)  falling  from  a  height  of  1 

'  Wundt's  Philosophisclie  Studien,  1883,  I.,  heft  4,  pp.  495  fE. 
'■'Comp.  Stumpf,  Toiipsychologie,  I.,  p.  364  f. 


LOWER  LIMIT   OF   SOUND.  373 

millimetre  (0.03937  inch).  Boltzmann  and  Topler  have  reached 
results  which  Hensen'  considers  to  be  as  accurate  as  possible.  By 
measuring  the  compression  of  the  air  at  the  end  of  an  organ-pipe  of 
181  vibrations  per  second,  they  calculated  that,  even  under  circum- 
stances not  as  favorable  as  possible,  the  ear  responds  with  sensation 
to  an  amphtude  in  the  vibration  of  the  molecules  of  the  au'  not  more 
than  0.00004  mm.  at  the  ear,  or  about  j\  the  wave-length  of  green 
light.  The  mechanical  work  done  upon  the  ear-drum  in  a  single 
vibration  of  such  small  intensity  is  reckoned  at  not  more  than  j^-g 
billionth  kilogrammetre  ;  or  only  about  J^  of  that  done  upon  the 
same  surface  of  the  pupils  of  the  eye  by  a  single  candle  at  the 
same  distance.  These  calculations  indicate  that  the  motions  in 
the  cochlea  which  excite  the  end-organs  of  sense  are  astonishingl}' 
minute — far  too  minute  to  be  observed  even  by  the  microscoioe. 
Yet  the  sharpness  of  hearing  maybe  enormously  increased  by  dis- 
ease. 

§  15.  Judgments  of  the  intensity  of  sounds  are  dependent  also 
upon  practice,  and  upon  other  psycho-physical  conditions  such  as 
determine  the  nicety  of  all  judgments  of  quality.  Small  impres- 
sions of  noise  are  apt  to  have  their  intensity  underestimated  ;  the 
inclination  to  do  this  has  been  attributed  to  the  influence  of  our 
custom  of  withdrawing  attention  from  them  altogether  under  ordi- 
nary circumstances.^  The  fact  that  sounds  to  which  we  become 
accustomed  lose  most  of  their  intensity  in  consciousness  must  be 
explained  chiefly  under  the  same  law  of  mental  habit  ;  it  cannot,  on 
the  other  hand,  be  largely  due  to  the  physiological  law  of  exhaus- 
tion. 

§  16.  Attention  was  early  called  to  the  law  of  judgment  in  esti- 
mating the  quantitative  relations  of  sensations  of  sight,  on  account 
of  its  connection  with  astronomical  observation.  In  the  preceding 
century  French  physicists  had  already  begun  to  investigate  the 
sensitiveness  of  the  eye  to  varying  intensities  of  light.  Bouguer,  in 
answer  to  the  question,  What  force  must  a  light  have  in  order  to 
make  a  more  feeble  one  disappear?  placed  the  fraction  of  least 
observable  difference  in  the  intensities  of  two  shadows  at  gJj.  That 
the  magnitudes  of  the  stars  are  not  to  be  classified  according  to 
their  absolute  brightness  as  determined  by  photometric  observa- 
tions was,  of  course,  assumed  by  Sir  John  Herschel  when  he  made 
the  latter  vary  in  the  series  1  :  ^  :  |-  :  J^,  while  the  former  vary  in 
the  series  1:2:3:4.  That  the  least  observable  difference  in  the 
intensity  of  two  sensations  of  sight  is  absolutely  much  smaller  for 

'  See  Hermann's  Handb.  d.  Physiol..  III.,  ii  ,  p.  117  f. 
^  So  Stumpf,  Tonpsychologie,  I.,  p.  388. 


374  THE   LAW   OF   WEBEE. 

those  of  the  lowest  grade  of  intensity  is  a  truth  needed  to  explain 
many  every-day  experiences.  For  example,  the  finer  gradations  of 
shade  in  a  lithograph  or  photograph  are  not  lost  when  we  take  it 
from  the  open  sunlight  into  a  rather  dimly  lighted  room  ;  we  can 
also  observe  them  through  smoked  glass,  if  it  be  not  too  black. 
Through  the  same  media  we  can  measure  rather  delicate  shades  of 
brightness  on  the  clouds.  We  observe,  however,  that  in  all  such 
cases  either  too  great  or  too  weak  intensity  of  the  light  destroys 
our  power  to  distinguish  the  finest  gradations  of  its  intensity. 

§  17.  It  has  already  been  shown  (p.  326)  that  the  retina  is  never 
free  from  light  of  its  own  which  has  a  varying  intensity  ;  this  fact 
greatlj'  increases  the  difficulty  of  fixing  accurately  either  the  lower 
limit  or  the  least  observable  difference  of  visual  sensations.  lu  the 
effort  to  apply  Weber's  law  to  sensations  of  color,  the  laws  of  change 
in  the  quality  operate  to  obscure  the  laws  of  change  in  the  quantity 
of  the  sensations.  Experiments  with  shadows  for  the  sake  of  testing 
Weber's  law  were  first  conducted  by  A.  W.  Volkmann  and  others, 
under  the  direction  of  Fechuer.'  By  measuring  the  distance  to 
which  a  candle  must  be  removed  from  an  object  in  order  that  the 
shadow  produced  by  its  light  might  disappear  in  that  of  another 
candle  of  like  intensity  situated  at  a  fixed  near  distance  from  the  ob- 
ject, the  quotient  for  the  least  observable  difference  was  found  to  be 
y-J-y.  This  quotient  was  also  found  to  remain  nearly  constant  for 
absolute  intensities  varying  from  1  to  38.79.  If,  however,  the  light 
of  the  background  diminished  to  0.36  in  intensity,  marked  varia- 
tions in  the  law  occxuTed  ;  the  difference  in  the  brightness  of  the  two 
shadows  had  then  to  be  greater  than  yj-o  to  be  observable.  Later 
experiments  of  the  same  observer  yielded  results  less  favorable  to 
Weber's  law.^  The  quotient  was  found  to  vary  from  j^  for  weak 
intensities  of  light  to  j^^j  for  stronger  intensities. 

By  using  rotating  disks  and  comparing  the  grayish  circles  made 
upon  them  when  revolving  rapidly,  through  the  admixture  of  small 
black  stripes  with  the  white  of  their  surfaces  ("Masson's  Disks"), 
Helmholtz  ^  found  the  medium  value  of  the  quotient  of  least  observ- 
able difference  to  be  y^^  ;  this  quotient  is  not  constant,  however,  and 
increases,  especially  for  sensations  near  the  upper  or  the  lower  limit. 
By  changing  the  method  somewhat,  Aubert  obtained  a  variation 
of  yJ-^  to  yI-o  i^  the  degree  of  sensitiveness  to  differences  in  the 
brightness  of  lights,  even  when  not  going  above  the  middle  of  the 
scale  of  intensity.     Experiments  with  such  intensities  as  lie  nearest 

'  See  Elemente  d.  Psychophysik,  p.  148  f. 

*  A.  W.  Volkmann,  Physiolog.  Untersuchungen,  I.,  p.  56  f. 

^  Physiologisclie  Optik,  p.  315  f. 


INTEXSITT    OF    COLOK-TOXES.  375 

the  limits  showed  much  greater  dej^artures  from  Weber's  law.  Just 
above  the  lower  limit,  au  addition  of  even  :^  to  ^  to  the  stimulus 
might  be  necessary  in  order  to  produce  an  observable  difference 
in  the  resulting  sensation.  Similar  results  have  been  obtained  by 
Delboeuf,  but,  on  the  whole,  more  favorable  to  Weber's  law  than 
the  results  of  Aubert. 

A  more  accurate  and  carefully  guarded  series  of  experiments 
than  any  of  the  foregoing  is  recently  reported  by  Dr.  Emil  Kj-ae- 
pelin.'  This  experimenter  used  the  method  of  just  observable  dif- 
ferences as  applied  to  Masson's  disks  when  looked  at  through  gxay 
glasses  of  varying  intensity.  The  utmost  care  seems  to  have  been 
taken  to  exclude  disturbances  from  changes  iu  the  adjustment  of 
the  eye,  retinal  exhaustion,  reflection  of  light  from  surrounding- 
objects,  etc.  Three  groups  of  experiments  were  conducted — one 
by  daylight,  one  by  candlelight,  one  by  lamplight.  Both  eyes 
were  experimented  upon  ;  and  both  directions  of  alteration  in  the 
intensity  of  the  stimulus  (stronger  following  weaker,  and  vice  versa) 
were  employed.  Kraepelin  concludes  that  for  the  unexhausted  eye, 
with  a  good  power  of  accommodation,  the  fraction  which  gives  the 
least  obseiwable  difference  remains  constant,  while  the  intensity  of 
the  light  varies  between  values  of  1,000  and  9.61  of  absolute  inten- 
sity as  fixed  for  his  experiments.  That  is,  within  these  limits  the 
law  of  Weber  holds  good  as  expressing  with  closely  approximating 
accuracy  the  results  of  experiment. 

The  experiments  of  Dobrowolsky  ^  and  Lamansky  ^  with  light  of 
the  different  spectral  color-tones  shows  that,  with  these  sensations 
also,  Weber's  law  holds  approximately  good  for  moderate  intensi- 
ties, but  is  subject  to  considerable  variations  a3  we  approach  the 
upper  and  the  lower  limits.  The  former  used  the  method  of  com- 
paring a  white  surface  with  one  in  which  colored  light  had  been 
mixed  with  the  white.  On  changing  the  absolute  intensity  of  the 
light  between  values  of  1  and  0.0302,  only  a  slight  variation  in  the 
quotient  indicating  the  least  observable  difference  of  intensity  ap- 
peared for  the  color  red.  This  quotient  was  found,  by  the  same 
observer,^  however,  to  be  very  different  for  different  color-tones  :  thus 
for  red,  -^^j ;  yellow,  J^- ;  green,  -^^ ;  blue,  y^^ ;  violet,  j^.  Laman- 
sky and  others  have  made  the  sensitiveness  to  changes  in  the  inten- 
sity of  color-tones  greatest  for  green  instead  of  violet ;  and  have  ob- 
tained other  results  different  from  those  obtained  by  Dobrowolsky. 

§  18.  The  minimum  of  the  intensity  of  light  ajDpreciable  by  the 

1  In  Wundt's  Philosopliisclie  Studien,  1884,  II.,  lieft  2,  pp.  306  ff. 

^  Pfluger"s  Arcliiv.  xii  .  p.  441  f. 

3  Arcliiv  f.  Ophthalmologie,  XVII.,  i.,  p.  123  f.     ■*  Ibid.,  XVIII.,  i.,  p.  74  f. 


376  THE   LAW   OF   WEBER. 

eve  under  the  most  favorable  circumstances  was  fixed  by  Aubert  at 
^^  of  that  reflected  from  white  paper  in  the  light  of  the  full-moon. 
This  result  can  only  be  considered  as  approximate.  The  individ- 
ual factor  in  all  such  calculations  must  be  held  to  be  very  large  and 
variable  ;  especially,  perhaps,  if  we  admit  that  there  is  a  class  of 
so-called  "  sensitives "  to  whom  the  ends  of  an  electro-magnet 
when  excited  appear  luminous,  as  Eeichenbach's  experiments  seem 
to  show.  Weber  applied  his  own  law  to  so-called  extensive  sensa- 
tions of  sight.  He  showed  that  in  judging  of  the  comparative 
length  of  lines  the  least  observable  difference  is,  for  each  person,  a 
tolerably  constant  fraction  of  the  absolute  length  of  the  line  with 
which  the  comparison  is  made.  This  fraction  is  different  for  differ- 
ent persons  ;  and  has  a  range  from  J-^  to  j^.  Fechner  '  defends 
the  validity  of  the  law  for  lines  of  lengths  varying  between  10  and 
240  mm.  (|  to  9^  in.),  with  the  eye  removed  from  1  ft.  to  800  mm. 
(12-32  in.).  The  lower  limit  for  such  cases  has  been  fixed  by  A.  W. 
Volkmann  at  lines  of  length  from  0.2  to  3.6  mm.  It  is  obvious, 
however,  that  we  are  here  not  dealing  with  pure  quantity  of  visual 
sensations,  but  with  judgments  of  local  relation  which,  in  case  the 
eyes  are  moved,  have  their  basis,  at  least  partly,  in  our  power  to  dis- 
criminate minute  differences  in  the  sensations  of  the  muscular*  sense 
connected  with  such  movements. 

§  19.  The  law  of  Weber  can,  of  course,  derive  little  or  no  sup- 
port from  sensations  of  taste  and  smell.  In  the  case  of  these  two 
senses  our  knowledge  of  both  series  of  quantities — of  the  intensity 
of  the  stimulus  and  of  the  amount  of  specific  sensation  which  re- 
sults from  its  application — is  altogether  too  inadequate  to  admit 
of  trustworthy  comparison.  We  cannot  measure  forms  of  energy 
like  those  by  which  smellable  particles  and  tastable  solutions  act 
on  the  end-organs  of  sense,  until  we  have  a  unit  of  measurement  and 
some  information  as  to  what  the  object  is  to  which  the  standard 
should  be  applied.  Nor  can  we  compare  amounts  of  sensations 
that  are  so  largely  matters  of  indiridual  origin  and  capricious 
change,  and  that  are  so  overlaid  with  other  forms  of  feeling,  as  are 
the  sensations  of  these  senses.  Moreover,  the  element  of  time — both 
as  respects  the  interval  elapsing  between  the  two  sensations  com- 
pared and  also  the  order  in  which  the  sensations  follow  each  other 
— is  here  a  very  important  influence. 

The  irdensl.ty  of  taste  depends  upon  a  variety  of  circumstances 
besides  the  objective  quantity  of  the  stimulus.  Among  these  cir- 
cumstances is  the  extent  of  surface  excited.     Camerer  ^  found  by 

'  Elemente  d.  Psychophysik,  i  ,  p   211  f. 

-  See  Zeitschr.  f.  Biologie,  1870,  VI.,  p.  440  f. 


MEASUREMENT   OF   TASTE.  377 

experimenting  with  common  salt  in  solutions  of  different  degrees 
of  concentration  that  the  number  of  correct  guesses  inci-eased  almost 
in  exact  proportion  to  the  number  of  gustatory  papillse  upon  which 
the  solutions  were  placed.  Certain  mechanical  and  thermic  con- 
ditions also  have  a  great  influence.  Substances  even  in  fluid  form, 
when  quickly  swallowed,  have  little  taste  ;  pressing  and  rubbing 
against  the  gustatory  organs,  movement  of  the  tastable  matter  in 
the  mouth,  increase  the  excitatory  effect  of  the  stimuli.  It  is 
doubtful  whether  this  effect  is  due  solely  to  the  mechanical  result 
of  spreading  the  stimulus  over  the  surface  and  urging  it  into  the 
pores  against  the  end-orgaus  of  the  sense,  or  in  part  also  to  some 
direct  physiological  cause.  The  influence  of  temperature  on  the 
intensity  of  sensations  of  taste  is  well  known.  Weber  showed  that 
if  the  tongue  is  held  for  |-  to  1  minute  in  very  cold  water,  or  in  wa- 
ter of  about  125°  Fahr.,  the  sweet  taste  of  sugar  can  no  longer 
be  perceived.  Cold  also  destroys  for  a  time  the  susceptibility  to 
bitter  tastes.  Keppler  '•  endeavored  to  test  Weber's  law  by  deter- 
mining the  sensitiveness  to  minute  changes  in  the  four  principal 
kinds  of  taste  ;  and  arrived  at  a  negative  result.  Fechner,  how- 
ever, considers  that  Keppler's  experiments  with  common  salt  confirm 
Weber's  law,  and  that  his  other  experiments  were  not  adapted  to 
yield  any  assured  result.  We  can  only  repeat  the  statement  that 
other  causes  than  mere  increase  in  the  quantity  of  the  stimulus  so 
largely  determine  the  intensity  of  the  resulting  sensations  as  to 
discredit  any  arguments  from  the  experiments  either  for  or  against 
applying  Weber's  law  to  sensations  of  taste. 

§  20.  The  exj)eriments  of  Valentin'  and  others,  to  determine  how 
weak  solutions  of  various  substances  will  excite  the  end-organs  of 
taste,  are  chiefly  valuable  as  gratifying  our  curiosity.  The  figures 
are  not  to  be  accepted  as  exact,  but  as  showing  in  general  the  ex- 
treme fineness  of  this  sense,  and  the  great  difference  of  different 
substances  in  their  power  to  excite  it.  Valentin  found,  for  exam- 
ple, that  0.24  gramme  of  a  solution  containing  1.2  per  cent,  of  cane- 
sugar  excited  the  sensation  of  sweet ;  a  solution  containing  j|-g- 
part  of  common  salt  was  scarcely  detectable  ;  of  sulphuric  acid 
To oVo'o'  could  be  discerned,  yro ottotf  ^°^  '■>  extract  of  aloes  contain- 
i^^o  g'o  oVTro  could  be  distinguished  from  distilled  water ;  -33^0 
of  sulphate  of  quinine  was  plainly  observable,  and  the  observer 
thought  he  could  detect  a  slight  trace  of  bitter  when  the  solution 
was  diluted  to  foTr^oin)  o^  ^^i^  substance.  In  general,  a  smaller 
absolute  quantity  of  stimulus,  when  in  a  relatively  concentrated 

'  Pfluger's  Archiv,  1869,  ii.,  p.  449  f. 

"^  In  his  Lehrb.  d.  Physiol,  d.  Menscheu,  2  ed.,  Abth.  2. 


378  THE   LAW    OF    WEBER. 

solution,  will  suffice  to  excite  tlie  end-organs  of  taste.'  It  will 
readily  be  seen  that  the  minimum  of  some  of  these  substances 
which  will  give  rise  to  a  sensation  under  the  most  favorable  cir- 
cumstances is  exceedingly  small. 

§  21.  The  intensity  of  sensations  of  smell  is  also  largely  depend- 
ent on  other  causes  than  changes  in  the  quantity  of  the  stimuli. 
The  amount  of  sensation  appears  to  be  largely  governed  by  the 
extent  of  surface  excited  ;  since  it  is  greater  when  we  smell  with 
both  nostrils,  and  with  the  current  of  inspiration  which  carries  the 
exciting  particles  over  more  of  the  sensitive  membrane.  No  as- 
siu'ed  results  on  this  point,  however,  have  yet  been  reached.  Val- 
entin supposes  that  a  smaller  number  of  odorous  particles  will 
excite  sensation  if  presented  in  a  concentrated  rather  than  a  dilute 
form.  When  the  intensity  of  the  stimulus  increases  beyond  a  cer- 
tain point,  the  character  of  the  resulting  sensation  changes — often- 
times from  a  pleasant  to  an  unpleasant  tone  of  feeling.  All  are 
familiar  with  the  fact  that  a  large  increase  of  some  smells — for 
example,  musk — does  not  give  the  same  kind  of  sensation.  This 
sense  has  a  great  degree  of  "sharpness,"  or  power  to  be  excited 
by  small  quantities  of  stimulus,  as  distinguished  from  "fineness," 
or  power  to  distinguish  minute  variations  in  the  sensations.  It  is 
undoubtedly  different  in  different  species  of  animals,  as  dependent 
upon  unknown  differences  in  their  psycho-physical  constitution  ; 
but  it  is  tolerably  uniform  among  men  where  there  is  the  same 
cultivation  of  it,  and  the  same  concentration  of  attention.  It  is 
well  known  that  certain  animals  have  an  astonishing  fineness  of 
smell,  and  are  able  by  it  even  to  detect  the  individual  variations 
that  are  quite  imperceptible  to  man.  Little  value  can  be  attached 
to  the  results  reached  by  experiments  to  fix  the  least  number  of 
smellable  substances  which  can  excite  the  human  end-organs  of 
this  sense.  In  general,  we  can  say  that  incredibly  small  quanti- 
ties of  some  substances  will  suffice.  Valentin  found  that  a  curx'ent 
of  air  containing  -g-oiiVoTr  of  vapor  of  bromine  excited  a  strong  un- 
pleasant sensation.  Atmosphere  polluted  with  even  jYiyl-u-o-Tr  ^^ 
sulphuretted  hydrogen  could  be  detected.  It  was  calculated  by 
this  observer  that  -jo"o  J-oo  u  "^^  ^  milligramme  of  alcoholic  extract  of 
musk  is  about  as  little  as  can  be  perceived.  The  effect  of  constant 
over-excitement  of  the  organs  of  this  sense,  in  deadening  their  sen- 
sibility, is  too  well  known  to  require  illustration.  No  argument 
for  or  against  Weber's  law  can  safely  be  drawn  from  sensations  of 
smell. 

§  22.  A  review  of  the  preceding  facts  confirms  what  was  previ- 
'  See  Camerer's  table  in  Pflijger's  Archiv,  ii. ,  p.  322. 


INTEllPEETATION   OF   THE  LAW.  379 

ously  said  as  to  the  unsatisfactory  nature  of  tlie  evidence  adduced 
in  proof  of  the  principle  which  is  thought  to  control  the  quantita- 
tive relations  of  our  sensations  and  their  stimuli.  At  best,  Weber's 
law  is  only  an  approximately  correct  statement  of  what  holds  true 
of  the  relative  intensity  of  certain  sensations  of  sight  and  hearing, 
and,  less  exactly,  of  pressure  and  the  muscular  sense,  when  these 
sensations  are  of  moderate  strength,  and  other  causes  for  variations 
in  their  intensity,  besides  objective  changes  in  the  amount  of  the 
stimulus,  are  as  far  as  possible  excluded.  In  general,  it  is  true  that 
the  amount  of  matter  pressing  on  the  skin,  or  lifted  by  moving  the 
arm  or  leg,  as  well  as  the  intensity  of  the  waves  of  light  and  sound 
acting  on  eye  and  ear,  must  increase  much  more  rapidly  than  does 
the  intensity  of  the  resulting  sensations,  as  estimated  by  comparing 
them  with  each  other  in  consciousness.  Within  certain  limits  for 
the  above-mentioned  four  kinds  of  sensation,  the  latter  scale  of 
quantities  is  ordinarily  related  to  the  former  about  as  an  arithmet- 
ical to  a  geometrical  series.  But  other  conditions  than  mere  increase 
in  the  objective  quantity  of  the  stimulus  largely  determine  its 
effect  upon  the  resulting  amount  of  sensation.  Stimuli  and  sensa- 
tions are  not  connected  quantitatively  in  such  a  simple  manner  that  we 
can  measure  one  off  in  terms  of  the  otJier ;  so  much  feeling  for  so 
much  amplitude  of  wave-lengths,  or  work  done  on  the  end-organs 
by  mechanical  pressure.  Numerous  factors,  some  of  which  are 
individual  and  extremely  obscure  and  variable,  constantly  mix 
with  the  piu'ely  quantitative  relations  between  sensations  and  their 
stimuli. 

§  23.  The  value  of  Weber's  law  is  so  restricted,  even  as  stating 
a  general  fact  of  expeiience,  that  it  would  seem  scarcely  necessary 
to  discuss  at  length  its  higher  significance.  Three  possible  modes 
of  explanation  have  all  had  their  defenders  ;  these  are  the  physio- 
logical, the  psycho-j^hysical,  and  the  psychological.  The  first  of 
the  three  assumes  that  the  physical  construction  of  the  nervous 
sj^stem,  including  chiefly  the  end-organs  of  sense  and  their  central 
representatives  and  connections,  is  such  as  to  supply  the  reason 
for  this  relation  between  the  intensity  of  sensations  and  that  of 
their  stimuli.  And  certainly,  if  we  were  to  make  any  assumption, 
it  would  be  that  the  quantitative  relation  between  the  last  ante- 
cedent molecular  changes  in  the  brain  and  the  mental  changes  to 
which  they  give  rise,  is  one  of  simple  proportion  ;  the  more  work 
done  by  means  of  the  excitation  in  the  appropriate  cerebral  centres, 
the  more  of  physical  basis  laid,  as  it  were,  for  a  resulting  quantity 
of  psychical  movement. 

If,  then,  the  sensations  vary  in  quantity  in  an  arithmetical  pro- 


380  THE   LAW    OF   WEBER. 

portion,  wliile  their  external  stimuli  vary  in  a  geometrical  propor- 
tion, the  explanation  of  the  fact  must  be  found  somewhere  in  the 
chain  of  events  between  the  external  stimuli  and  the  nerve-commo- 
tions set  up  as  a  result  in  the  appropriate  centres  of  the  brain.  And 
without  doubt  the  explanation  of  so  much  as  is  true  of  Weber's  law 
lies  largely  in  physiological  causes  ;  but  our  knowledge  of  the  struct- 
ure and  function  of  the  end-organs  of  sense,  and  especially  of  their 
cerebral  representative  elements,  is  so  incomplete  that  no  satisfac- 
tory statements  can  be  made  on  this  point.  In  all  of  the  senses,  the 
end-organs  profoundly  modify  the  intensity  of  the  stimulus  they  re- 
ceive. In  the  so-called  chemical  senses  (smell,  taste,  sight)  a  pro- 
found quantitative  modification  takes  place,  even  before  the  stimu- 
lus reaches  the  fibrils  of  the  sensory  nerve.  In  the  case  of  the 
mechanical  sense  of  hearing  we  cannot  say  how  naucli  of  the  efifect 
stated  in  Weber's  law  may  not  have  been  gained  even  before  the 
acoustic  waves  set  agoing  the  nervous  elements  of  the  organ  of 
Corti.  As  to  profounder  modifications  in  the  same  direction  by 
reason  of  the  interaction  of  different  nerve-elements  in  the  brain  we 
are  yet  more  ignorant.  And  although  we  can  have  little  confidence 
in  Wundt's  '  theory  of  an  "  apperception-centre  "  and  its  influence 
in  accounting  for  Weber's  law,  we  cannot  deny  the  general  assump- 
tion on  which  that  theory  is  based. 

Tlie  psycho -physical  explanation  of  Weber's  law  is  that  adopted 
by  Fechuer.  This  explanation  insists  upon  making  the  law  one  of 
the  utmost  generality  and  of  the  highest  import  as  stating  the  re- 
lations between  organic  and  spiritual  activities.  Although  Fech- 
ner's  view  confessedly  grew  out  of  his  speculation  that  body  and 
mind  are  only  two  phenomenal  aspects,  as  it  were,  of  one  and  the 
same  underlying  reality,^  it  has  been  defended  by  him  with  a  great 
amount  of  mathematical  science  and  experimental  research.  No 
other  form  of  explanation,  howevei',  takes  us  so  much  into  the 
regions  of  utter  obscurity.  Why  the  quantitative  relations  of  body 
and  mind  should  be  such,  and  such  only,  that  a  geometrical  series 
of  changes  in  the  one  should  invariably  be  represented  by  an  arith- 
metical series  of  changes  in  the  other,  must  indeed  remain  an  ulti- 
mate mystery.  And  the  experimental  proof  of  Weber's  law  is  as 
yet  much  too  incomplete  to  make  us  ready  to  accept  it  as  an  ulti- 
mate psycho-physical  principle. 

The  psychological  explanation  of  Weber's  law  resolves  it  into  a 
special  case  under  the  greater  law  of  the  relativity  of  our  inner 

*  Comp.  his  Physiol.  Psychologie,  i. ,  p  351  f . ,  and  ii. ,  p.  207  f .  ;  also 
Philosophische  Studien,  1883,  II.,  heft  1,  p.  31  f. 

'  Id  proof,  see  his  Revision  d.  Hauptpuncte  d.  Psychophysik,  p.  13  f. 


THE  LAW   OF   EELATIVITT.  381 

states.  It  is  not  so  much,  then,  a  law  of  the  absokite  quantity  of 
sensations  as  dependent  on  stimuli,  but  rather  a  law  of  our  ap- 
prehension in  consciousness  of  the  relation  of  our  own  feelings.  In 
general,  it  may  be  said  that  every  mental  state  has  its  value  de- 
tfrmined,  both  as  respects  its  quahty  and  its  so-called  quantity,  by 
its  relation  to  other  states.  It  is  the  amount  of  change  rather  than 
the  absolute  amount  of  feeling  which  the  mental  apperception  esti- 
mates. That  the  psychological  explanation  is  needed  to  account 
for  the  facts  there  can  be  no  doubt  when  we  consider  how  impor- 
tant are  the  elements  of  attention,  mental  habit,  power  of  acute 
discrimination,  etc.,  in  determining  our  estimates  of  the  quanti- 
tative relations  of  our  sensations.  Estimates — that  is,  acts  of  the 
comparing  judgment,  are  involved  in  the  experience  upon  which 
reliance  is  placed  for  a  demonstration  of  Weber's  law.  Further 
discussion  of  the  significance  and  extent  in  application  of  the  men- 
tal law  of  relativity  will  appear  in  other  connections.  The  subject 
of  the  quantity  of  sensation  as  a  matter  of  psycho-physical  investi- 
gation is  fitly  closed  with  the  following  quotation  from  Wundt : ' 
"In  the  imperfect  condition  of  cerebral  physiology,  we  are  not 
seldom  in  a  position  to  recognize  the  psychological  formulating  of 
certain  laws,  the  physiological  meaning  of  which  still  lies  in  ob- 
scurity or  belongs  to  the  domain  of  hypothesis." 

1  Physiol.  Psychologie,  i.,  p.  353. 


CHAPTER   VI. 

THE  PEESENTATIONS  OF  SENSE. 

§  1.  Sensations  are,  primarily  consiclerecl,  modes  of  our  being 
affected  ;  but  the  objects  of  sense  are  known  as  real  beings,  which 
are  assumed  to  exist  independent  of  the  affections  of  our  minds, 
and  to  have  their  inherent  quahties  disclosed  to  us  through  the 
operation  of  the  senses.  There  is  a  wide  interval,"  however,  between 
our  consciousness  of  being  ourselves  affected  and  the  perception 
of  "  things  "  as  having  qualities  resembling  our  mental  states  or  re- 
vealed by  them.  This  interval  is  filled,  in  nature,  by  the  develop- 
ment of  mind  as  conditioned  upon  its  environment  of  sense-stimuli; 
it  must  be  filled  in  psychological  theory,  by  a  description  of  the 
process  of  development.  Physiological  Psychology  constructs  such 
theory  as  much  as  possible  on  a  basis  of  experiment  to  determine 
how  the  various  steps  in  the  mental  development  are  related  to  the 
changes  which  the  stimuli  jDroduce  in  the  nervous  system,  espe- 
cially, of  course,  in  the  organs  of  sense.  Upon  this  work  of  con- 
struction it  has  expended  its  choicest  resources  and  utmost  ingenu- 
ity. Its  efforts  are  yet  far  from  being  completely  successful.  Many 
of  the  secondary  jDrinciples,  and  even  questions  of  fact,  are  still  un- 
settled ;  no  theor}'  of  perception  that  will  account  satisfactorily  for 
all  the  admitted  truths  has  hitherto  been  discovered.  Nor  is  this 
lack  of  complete  success  surprising,  when  we  consider  how  rapid 
and  complex  are  the  processes  which  combine  to  form  the  world  of 
sensible  objects  ;  as  well  as  how  entire  is  the  loss  suffered  by  memory 
and  consciousness  of  those  details  which  served  as  a  basis  for  the 
earlier  and  most  significant  stages  of  the  development. 

Nor  should  we  fail  to  take  account  of  the  fact  that  the  mechan- 
ism of  both  nervous  system  and  mind  operates  as  rendered  native 
to  the  individual  by  his  inheriting  the  results  of  many  ages  of  an- 
cestral experience.  The  psychologist  does  not  remember  by  what 
stages  he  first  learned  to  see  or  feel  the  extended  and  external  ob- 
jects of  sense.  The  child  cannot  describe  the  process  to  the  psy- 
chologist ;  the  child  is  farther  from  his  own  infantile  experience  in 
this  regard  than  the  philosopher  is  from  that  of  the  child.     It  is 


eOMMOW-SEFSE   VIEW   OF   PERCEPTIOlSr.  383 

not  even  likely  that,  if  the  infant  were  endowed  with  the  developed 
power  of  searching  his  own  consciousness,  and  of  describing  its 
contents,  he  could  discover  and  impart  what  is  needed  in  order  to 
explain  the  process  of  his  own  mental  development.  In  all  stages 
of  human  growth  the  analyzable  contents  of  consciousness  represent 
only  very  imperfectly  the  nature  of  the  basis  upon  which  they  rest. 

§  2.  Scientific  analysis  of  the  process  of  perception  corrects  in 
many  particulars  the  so-called  "common-sense"  view.  The  convic- 
tion which  everyone  has  on  opening  the  eyes  upon  a  landscape,  for 
example,  is  undoubtedly  that  of  being  immediately  impressed  with 
a  faithful  copy  of  extra-mental  reahty.  Some  of  the  objects  are  seen 
as  larger,  others  smaller,  some  in  the  foreground  near  by,  and  others 
more  remote  ;  but  all  have  that  solid,  substantial  character  which 
makes  them  things  as  distinguished  from  the  images  of  revery  or 
dreaming.  But  it  is  precisely  the  acquired  power  thus  to  construct 
the  landscape  which  psychological  science  tries  to  explain.  The  ordi- 
nary conviction  accepts  the  aj^parent  fact  of  an  immediate  and  certain 
knowledge  of  these  things  through  the  eyes,  as  though  it  were  matter- 
of-course  and  needed  no  explanation.  We  must  begin  by  removing 
certain  assumptions  obviously  involved  in  the  ordinary  conviction. 

The  forms  of  being  and  happening  in  the  world,  outside  of  the 
body,  furnish  in  themselves  no  explanation  whatever  of  the  presen- 
tations of  sense. '  This  is  as  true  of  the  colored  or  smooth  extension 
of  an  object  as  it  is  of  its  sweet  taste  or  disagreeable  smell.  "What- 
ever exists  (?.x^ra-mentally,  so  far  as  its  pure  existence  goes,  is  of  no 
account  to  the  mind.  It  is  only  as  so-called  "things  "  act  upon  us, 
or — in  other  words — get  themselves  exjjressed  within  the  mind,  by 
causing  changes  in  our  mental  states,  that  any  theory  of  knowledge 
by  the  senses  can  make  use  of  them.  Centuries  ago  the  popular 
feeling  was  framed  into  a  doctrine  that  semi-spiritualized  copies 
of  the  material  realities  enter  the  body  through  the  senses  and  meet 
the  mind  somewhere  within ;  or,  that  the  mind  itself,  passing  out 
through  the  openings  of  sense  in  semi-materialized  form,  embraces 
and  so  knows  these  realities.  The  time  for  all  similar  crude  theo- 
ries of  knowledge  by  the  senses  ought,  however,  to  have  long  gone 
by.  And  yet  fragments  or  suggestions  of  essentially  the  same 
assumptions  are  still  frequent  enough. 

What  is  true  of  all  that  exists  and  happens  outside  of  the  body 
is  just  as  true  of  all  the  bodily  conditions  and  processes.  Strictly 
speaking,  they  can  in  themselves  furnish  no  explanation  for  the  rise 
and  development  of  the  presentations  of  sense.     Only  mental  factors 

'  Comp.  Volkmann  von  Volkmar,  Lehrbucli  d.  Psycliologie,  Cothen,  1885, 
II..  p.  1  f .  ;  and  Lotze,  Medicinische  Psycliologie,  Leipzig,  1852,  p.  325  f. 


384  THE   SYNTHESIS    OF    SENSATIO]S"S. 

can  be  built  into  mental  products.  The  simple  sensations  are  in 
themselves  always  psychical  phenomena,  and  are  to  be  referred,  as 
modes  of  its  being  and  action,  to  the  subject  called  "  mind."  It  is 
only  when  considered  in  this  way  that  they  afford,  by  their  charac- 
teristic qualities  and  modes  of  combination,  any  explanation  of  the 
resulting  knowledge  of  things.  The  image  on  the  retina,  for  exam- 
ple, is  a  necessary  jDhysieal  condition  of  the  clear  vision  of  outside 
objects  ;  it  may  also  become  an  object  for  the  inspection  of  another 
observer.  But  the  retinal  image  never  becomes  a  kind  of  inner 
object  for  one's  own  brain  or  mind.  Nothing  in  its  construction, 
in  itself  considered — that  is,  as  independent  of  the  system  of  local- 
ized sensations  which  result  on  the  other  or  psychical  side  of  the 
transaction — helps  to  explain  the  act  of  vision.  What  is  true  of  the 
peripheral  is  also  true  of  the  central  organs  of  sense.  There  is  no 
image  in  the  brain  transmitted  in  exact  copy  from  the  retina  by 
the  optic  nerve  to  its  central  nerve-fibres  and  nerve-cells  ;  if  there 
were  such  a  brain-image,  we  should  need  another  eye  connected 
with  a  second  brain  and  mind  to  read  it.  The  mind  is  never  to  be 
conceived  of  as  contemplating  a  spatial  picture  of  its  object  formed 
somewhere  within  the  cerebral  substance. 

Even  more  obvious  is  the  worthlessness,  for  purposes  of  strictly 
psychological  analysis,  of  all  theory  as  to  the  precise  spatial  arrange- 
ment of  the  fibrils  of  sensory  nerves  within  the  shin  or  muscular 
fibre.  That  such  fibrils  exist  in  the  muscles  has  apparently  been  de- 
monstrated by  Sachs  and  others  (comp.  Chap.  IV.,  §  20) ;  the  nervous 
impulses  occasioned  in  them,  when  conveyed  to  the  central  organs, 
are  probably  one  main  physical  basis  of  those  feelings  of  innerva- 
tion, of  being  in  the  body,  etc.,  which  enter  as  essential  factors  into 
the  spatial  perception -field  of  our  own  periphery.'  But  it  is  the 
muscular  sensations,  as  modes  of  the  affection  of  mind,  which  per- 
form this  ofl&ce.  We  have  nothing  approaching  an  immediate  cog- 
nition of  the  extended  net-work  of  sensory  fibrils  in  the  skin  or 
muscles  ;  much  less  of  the  extended  muscle  or  area  of  the  skin. 
No  copy  in  space-form  of  the  various  simultaneous  or  successive 
rubbings  and  stretchings  of  these  peripheral  fibrils  is  propagated 
to  the  brain  ;  and  if  it  were,  the  mind  could  not  be  regarded  as 
taking  account  of  any  of  these  neural  processes. 

A  fui'ther  negative  statement  may  be  made  wdth  entire  confidence. 
The  place  at  which  each  organ  of  sense  is  found  in  the  periphery  of 
the  body,  or  the  place  at  which  any  such  organ  is  acted  on  by  the 
stimulus,  cannot  of  itself  furnish  a  reason  for  the  spatial  perception 
of  such  place  and  for  distinguishing  it  from  other  places  near  or 
'  See  an  article  in  Mind,  by  G.  Stanley  Hall,  III.  (1878),  pp.  433  ff. 


TOUCHING   AND   BEING  TOUCHED.  401 

tions  are  localized  ;  we  see  some  of  the  same  parts  as  projected  in 
space  before  our  eyes.  Objects  that  are  not  a  part  of  ourselves  are 
given  to  us  as  projected  eccentrically,  either  by  touch  through  their 
being  in  contact  vpith  the  skin  and  occasioning  sensations  of  mus- 
cular exertion,  or  by  sight  as  having  distance  in  its  field  of  vision. 
Localization  and  projection  are  not  to  be  regarded  as  two  phases  of 
one  and  the  same  process  ;  we  do  not  first  have  the  presentations 
of  sense  as  parts  of  the  periphery  of  our  bodies,  and  then,  on  further 
experience,  push  them  beyond  this  perij)hery,  either  to  an  infini- 
tesimal distance  or  to  one  remote.  Localization  and  eccentric  pro- 
jection are  rather  two  processes,  largely  unlike,  which  go  on  con- 
temjDoraneously  and  are  set  up  chiefly  on  the  basis  of  different 
classes  of  sensations. 

Where  two  j)arts  of  the  sensitive  skin  of  our  own  bodies  come 
together  the  conditions  for  both  of  the  above-mentioned  processes 
are  fulfilled.  Accoi-dingly,  one  part  has  localized  in  it  those  com- 
plex sensations  which  make  us  aware  that  this  joart  of  our  body  is 
touching  something  ;  the  other  has  localized  in  it  those  sensations 
which  make  us  aware  that  this  part  is  being  touched  by  something. 
Which  of  the  two  j)arts  shall  be  regarded  as  touching,  and  which  as 
being  touched,  depends  on  various  considerations.  Those  mem- 
bers of  the  body  which  are  most  used  in  active  touch  are  generally 
known  as  touching,  and  the  less  active  parts  as  being  touched.  For 
example,  if  with  closed  eyes  the  forehead  be  moved  across  the  sta- 
tionary tip  of  a  finger,  the  latter  will  appear  to  be  the  active  organ 
of  touch.  Comparatively  insensitive  areas  of  the  skin  are  less  likely 
to  be  presented  to  the  mind  as  touching  other  more  sensitive  parts ; 
callous  spots,  indurated  surfaces,  etc.,  seem,  as  a  rule,  to  be  touched. 
Parts  of  the  body  which  lose  all  sensitiveness  come  to  be  regarded 
as  external  things.  If  the  tip  of  a  finger  of  normal  sensitiveness  be 
brought  into  contact  with  the  callous  tip  of  the  corresponding  fin- 
ger of  the  other  hand,  the  former  will  be  known  as  touching  and 
the  latter  as  being  touched.  The  direction  of  attention  often  deter- 
mines the  strife,  as  it  were,  between  the  motifs  to  localization  and 
those  to  eccentric  projection.  We  ordinarily  strive  to  gain  knowl- 
edge of  the  qualities  of  some  outside  object,  rather  than  of  the  con- 
dition of  our  own  peripher}^  with  respect  to  the  sensations  localized 
in  it ;  the  attention  is  therefore  directed  to  those  series  of  sensations 
which  form  the  basis  of  eccentric  projection,  even  when  some  part 
of  our  own  sensitive  organism  is  the  object  known.  But  sensations 
which  ai'e  accompanied  by  obtrusive  feeling  of  some  kind  furnish 
superior  grounds  for  localization.  We  locate  pains,  pricks,  severe 
pressure,  sensations  of  creeping,  and  tickling,  in  the  body.  Li  gen- 
26 


402  PEECEPTIONS    OF   THE   LOWER   SENSES. 

eral,  then,  a  strong  tone  of  feeling  with  the  sensation  favors  the 
process  of  localizing ;  tonelessness  of  sensation  favors  the  jDrocess 
of  objectifying.' 

A  system  of  localized  sensations,  gained  chiefly  by  pressure  of 
the  skin  and  muscles,  and  accompanied  by  a  strong  tone  of  feeling, 
gives  us  the  primary  field  of  the  body  as  known  to  touch.  Certain 
points  of  starting,  as  it  were,  must  first  be  fixed  in  the  process  of 
localizing  ;  this  process  then  goes  on  by  relating  all  other  localized 
sensations  to  these  points  of  starting.  But  by  eccentric  projection, 
the  system  of  muscular  sensations  of  movement  and  the  system  of 
visual  sensations  are  combined  to  develoj)  our  perceptions  of  ob- 
jective space  ■with  its  three  dimensions.  The  sensations  of  touch 
are  subsequently  projected  into  a  space  thus  originally  constituted 
by  combined  muscular  sensations  and  visual  sensations.  The  eye 
and  hand  in  motion,  therefore,  project  their  extended  objects  into 
a  space  which  they  develop  themselves  ;  while  the  ear  and  the  nose 
project  their  perceptions  into  a  space  which  they  are  compelled  to 
assume  on  the  authority  of  the  other  senses. 

The  foregoing  principles  must  now  be  illustrated  and  confirmed 
by  a  brief  statement  of  facts  which  relate  to  the  formation  and  de- 
velopment of  presentations  of  sense  by  a  synthesis  of  simple  sen- 
sations. Attention  will,  for  obvious  reasons,  be  directed  almost 
exclusively  to  those  presentations  of  sense  which  come  through  the 
eye  and  skin,  including  in  both  the  influence  of  muscular  sensa- 
tions. 

§  17.  Perceptions  of  Smell  differ  only  in  fineness,  duration,  and  ac- 
companying tone  of  feeling  ;  they  have  no  size  or  shape,  no  spatial 
properties  of  any  kind.  They  cannot  even  be  said  to  be  localized. 
Fineness  of  smell,  or  power  to  make  minute  distinctions  in  quality, 
and  so  infer  the  presence  or  direction  of  an  object  previously  known 
to  excite  such  quality  of  sensations,  diffei'S  greatly  in  different  spe- 
cies of  animals  and  in  different  individuals  of  the  same  species. 
The  exploits  of  some  animals  give  ground  for  the  conjecture  that 
every  species,  and  even  every  individual,  has  an  odor  of  its  own.'^ 
The  direction  and  nature  of  the  object  which  causes  the  sensations 
are  judged  by  variations  of  intensity  on  turning  the  head,  or  on 
approaching  or  receding  from  the  object.  Sensations  of  smell  are 
known  to  come  through  the  nose,  by  localizing  there  the  accom- 

'  Compare  Volkmann  von  Volkmar,  Lehrbucli  der  Psycliologie,  II.,  p. 
12G  f. 

-  See  the  articles  of  Donhoff,  in  Archiv  f.  Anat.,  Physiol.,  etc.,  Physiolog. 
Abth  ,  p.  750  f.  (1874) ;  and  Jiiger,  in  Zeitschr.  f.  wissensch.  Zool.,  xxvii.,  p. 
319  f.  (1876). 


TASTE   AND   HEAEING.  403 

panying  muscular  and  tactual  sensations  with  their  strong  tone  of 
feeling.  This  is  readily  done,  since  we  draw  the  air  through  the 
nostrils  and  feel  its  double  effects  in  producing  the  two  classes  of 
sensations.  As  to  the  simultaneous  influence  of  two  smells,  little 
is  known  beyond  the  statement  of  Valentin,  that  the  stronger 
overwhelms  the  weaker.  The  power  of  discrimination  may,  of 
course,  be  cultivated  in  this  sense  as  in  every  other.' 

§  18.  Most  of  the  remarks  just  made  as  to  perceptions  of  smell 
apply  also  to  Perceptions  of  Taste.  Sensations  of  taste,  however,  are 
much  more  closely  connected  with  those  of  touch  ;  since  the  tongue 
is  a  chief  organ  of  active  touch.  It  is  the  tactual  and  muscular 
sensations,  and  not  the  purely  qualitative  affections  of  taste,  which 
are  localized  in  the  mouth.  Concerning  contrast  and  comjDensation 
of  tastes,  little  is  known  which  does  not  belong  to  ordinary  experi- 
ence. Valentin "  alleges  that  when  a  sour  mass  is  laid  on  one  half, 
and  a  bitter  mass  on  the  other  half,  of  the  root  of  the  tongue,  the 
predominating  taste  may  sometimes  be  determined  by  our  choice. 
It  is  well  known  that  certain  tastes  compensate  each  other,  as  it 
were,  in  experience,  without  any  chemical  equivalence  of  their  prop- 
erties. The  sugar  neutralizes  the  acid  of  the  lemonade,  not  in  the 
vessel  that  contains  the  mixture,  but  in  the  nervous  system  of  him 
who  drinks  it  Brilcke  holds  ^  that  the  neutralizing  of  one  sensa- 
tion of  taste  by  the  other  takes  place  in  the  brain.  The  sensation 
of  bitter  is  es^Decially  difficult  to  cover  or  neutralize. 

§19.  Perceptions  of  Hearing  n&x.i  demand  consideration.  More 
difficulty  accompanies  the  effort  to  establish  the  proposition  that 
sensations  of  sound  are  not  directly  localized,  but  are  projected 
in  a  space  constituted  chiefly  by  the  eye  and  the  hand,  through 
complicated  indirect  inferences.  Such  a  proposition  is,  however, 
undoubtedly  true.  The  locahzing  of  the  area  of  the  body  which 
serves  as  the  organ  of  the  sensations  of  sound,  the  knowledge  that 
we  hear  loith  the  ear,  is  accomplished  chiefly  through  those  sen- 
sations of  shock  to  the  muscles  and  skin  of  the  region  which  come 
from  loud  and  massive  or  piercing  sounds.  Sensations  of  sound 
originating  through  excitement  within  or  very  near  to  the  ear  itself 
are  called  "entotic."  A  great  part  of  such  sounds,  if  not  all  of  them, 
are  transmitted  through  the  tympanum.  Perceptions  combined  of 
such  sensations  may  be  located  either  within  the  ear  or  at  some  dis- 

'  On  the  whole  subject  see  von  Vintschgau' s  monograph,  in  Hermann,  Handb. 
d.  Physiol.,  III.,  ii.,  pp.  225  ff. 

^  Lehrbuch  der  Physiol,  d.  Menschen,  etc.,  Abth.  ii.,  p.  308  (second  edi- 
tion). 

^  Vorlesungen  liber  Physiol,  (ed.  1884),  ii. ,  p.  262. 


404  PERCEPTIOiSrS   OF   THE   LOWER   SEN"SES. 

tance  from  the  bod}',  according  to  previous  associations  and  oppor- 
tunities for  judgment.  The  sound  produced  by  the  vibration  of  the 
adjoining  muscles,  and  heard  as  a  low  musical  tone  when  the  fin- 
gers are  pressed  in  the  ears  (especially  if  the  teeth  are  tightly  set 
together),  is  located  in  the  head  by  the  help  of  its  accompanying 
sensations  of  other  kinds.  The  same  thing  is  true  of  the  crackling 
noise  sometimes  produced  by  yawning,  or  of  the  whirring  occasioned 
by  the  passing  of  the  blood  through  the  neighboring  large  blood- 
vessels. In  the  same  way  we  learn  to  hear  the  beating  of  our  own 
hearts,  or  the  noise  of  air  in  our  respiration.  But  the  click  of  the 
valves  of  the  internal  organ  may,  when  experience  gained  through 
tactual  and  muscular  sensation  fails  us,  be  located  in  the  watch 
under  our  pillow;  just  as  the  singing  or  ringing  "in  the  ears" 
produced  by  quinine,  or  cerebral  excitement  otherwise  occasioned, 
may  be  located  in  a  cricket  supposed  to  be  upon  the  sill  of  the  open 
window.  Li  certain  pathological  cases  the  power  to  distinguish 
between  entotic  sounds  and  those  having  an  external  origin  is  al- 
most wholly  lost. 

§  20.  We  can  orientate  ourselves  in  space  with  reference  to  ex- 
ternal sounds  with  great  speed  and  considerable  precision,  but  as 
an  acquired  art  difFering  in  different  individuals  and  dependent 
upon  attention  and  previous  experience.  E.  H.  Weber  thought 
that  we  tell  the  direction  of  sounds  by  the  help  of  the  feeling  of 
the  swing  of  the  ear-drum ;  and  instanced,  in  proof,  that  this 
eccentric  projection  is  hindered  by  filling  the  external  passage 
of  the  ear  with  water.  When  using  both  ears  and  moving  the 
head  freely  in  space,  we  undoubtedly  determine  the  direction  of 
sounds  by  differences  in  the  intensity  of  the  sensation  dependent 
upon  changes  in  the  relative  position  of  both  ears.  Kayleigh ' 
found  that,  in  a  quiet  place  under  favorable  circumstances,  the 
direction  of  a  word  or  letter  uttered  in  a  natural  voice  could  be 
given  with  considerable  accuracy  ;  that  of  a  musical  tone  much 
less  accurately.  The  direction  of  a  sound  from  a  tuning-fork 
could  not  be  given  when  it  was  held  either  behind  or  before,  but 
could  be  given  if  the  fork  was  held  to  the  right  or  to  the  left.  It 
is  said  that  the  conducting  of  an  intermitting  cui'rent  from  a  tele- 
phone through  both  ears  causes  a  perception  of  tone  localized  in  the 
median  plane  of  the  head. 

Such  facts  as  the  foregoing  introduce  us  to  the  theory  of  "acous- 
tic shadows,"  or  of  the  amount  of  "covering"  power  which  the 
sound  produced  by  the  waves  of  a  given  intensity  entering  one 
ear  would  have  upon  the  sound  produced  by  waves  of  a  difterent 
'Nature,  XIV.,  p.  33. 


THE  EXPERIMENTS  OF  WEBER.  405 

intensity  entering  the  other  ear.  It  does  not  appear  to  Hensen/ 
however,  that  the  prompt  and  accurate  locahzation  of  direction 
possible  to  some  ears  can  be  wholly  accounted  for  by  the  theory  of 
acoustic  shadows.  Some  other  form  of  feeling,  possibly  connected 
with  the  remarkable  arrangement  of  the  semicircular  canals,  may 
blend  with  the  estimate  of  differences  in  intensity  to  form  a  basis  for 
judgment.  Von  Kries  and  Auerbach  found  that  the  promptness 
with  which  the  direction  of  the  noise  from  an  electric  spark  can  be 
localized  depends  upon  its  relation  to  the  circuit  of  the  head.^ 

Our  perceptions  of  the  absolute  distance  of  sounding  objects  are 
entirely  dependent  upon  our  knowledge  of  the  quality  and  quantity 
of  the  sounds  ordinarily  proceeding  from  them  ;  they  are,  that  is 
to  say,  not  presentations  of  sense,  but  indirect  estimates  as  to  the 
objective  cause  of  the  sensations  immediately  experienced.  It  has 
been  claimed  that  a  change  in  the  relation  of  the  partial  tones  to 
the  fundamental  tone,  dependent  upon  the  remoteness  of  the  place 
of  origin  of  the  compound  clang,  aids  our  estimate  of  distance  by 
sound. 

§  21.  An  account  of  the  process  by  which  a  Field  of  Touch  is  con- 
structed, and  extended  objects  are  known  as  in  contact  with  the 
skin  at  definite  points  or  areas  of  it,  must  begin  by  enumerating  the 
data  which  the  mind  has  for  such  activity.  The  most  important  of 
these  data  are  indicated  by  certain  facts  as  to  the  fineness  of  the 
so-called  "  sense  of  locality  "  belonging  to  the  skin.  E.  H.  Weber 
first  estabhshed  a  rule  for  measuring  the  degree  of  this  fineness  ac- 
curately ;  he  also  mapped  out  the  entire  field  of  the  surface  of  the 
body  into  areas  differing  greatly  in  their  fineness.^  For  a  measur- 
ing instrument  he  used  the  two  points  of  a  pair  of  dividers,  blunted 
so  as  to  prevent  the  sensation  of  being  pricked  ;  the  princijDle  of 
measurement  was  that  the  minimum  distance  apart  at  which  the 
two  points,  when  touching  the  skin  of  any  region,  are  felt  as  two  local- 
ized sensations  is  the  measure  of  the  sensitiveness  to  local  distinction 
of  that  region.  The  following  table  gives  some  of  the  results  of 
Weber's  experiments ;  the  figures  indicate  the  number  of  milli- 
meters ■"  apart  which  the  points  of  the  dividers  were  when  the  given 
area  of  the  organ  was  just  able  to  distinguish  them  : 

'  In  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  136. 

2  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth  ,  1877,  p.  331  f. 

^  Annot.  Anatom.,  vii.,  p.  4  f.  ;  Wagner's  Handworterb.  d.  Physiol.,  HI., 
Abth.  ii. ,  p.  529  f . 

^  The  numbers  were  given  by  Weber  in  Parisian  lines ;  in  the  table  they  are 
taken  from  Wundt,  Physiolog.  Psychologie,  ii.,  p.  7,  who  has  reduced  them  to 
even  millimeters. 


406  THE   FIELD   OF   TOUCH. 

Tip  of  the  tongue ■ 1 

Volar  side  of  the  last  phalanx  of  the  finger   2 

Red  part  of  the  lips 5 

Volar  side  of  the  second  and  dorsal  side  of  the  third  phalanx  of  the  finger  .     7 

White  of  the  lips,  and  metacarpus  of  the  thumb 9 

Cheek,  and  plantar  side  of  the  last  phalanx  of  the  great-toe 11 

Dorsal  side  of  the  first  phalanx  of  the  finger 16 

Skin  on  the  back  part  of  cheek-bone,  and  forehead 23 

Back  of  the  hand 31 

Knee-pan,  and  surrounding  region 86 

Forearm,  lower  leg,  back  of  the  foot  near  the  toes 40 

Skin  of  the  nape,  and  of  the  back  in  the  five  upper  cervical  vertebrae 54 

Skin  of  the  middle  of  the  back,  and  of  the  upper  arm  and  leg 68 

"Weber  also  found  that  the  fineness  of  the  sense  of  loeaHty  is 
greater  in  a  transverse  than  in  a  longitudinal  direction,  on  both  arms 
and  legs.  On  these  surfaces  of  the  skin  the  "  sensation-circles,"  or 
areas  within  which  the  minimum  distances  of  the  dividers'  points 
are  felt  as  two  points,  have  an  elliptical  shape,  with  their  long  axes 
up  and  down.  That  the  size  of  the  sensation-circles,  or  the  fineness 
of  the  sense  of  locality,  largely  forms  the  basis  for  our  judgments 
of  the  position,  number,  and  magnitude  of  the  localized  sensations 
in  the  field  of  touch  may  be  shown  by  a  simple  experiment.  If 
the  points  of  the  dividers  be  separated  somewhat  less  than  is  neces- 
sary in  order  to  distinguish  them  as  two  on  the  cheek  just  in  front 
of  the  ear,  and  then  (the  distance  apart  of  the  points  remaining  un- 
changed) be  slowly  moved  until  one  point  rests  upon  the  upper  and 
the  other  upon  the  lower  lip,  to  a  person  blindfold,  and  unpreju- 
diced by  knowing  what  is  to  take  place,  the  point  first  felt  as  one 
will  appear  to  become  two,  and  then  the  two  recede  from  each 
other  continually  as  the  parts  with  a  finer  sense  of  locality  are  trav- 
ersed. The  same  experiment  may  be  tried  upon  any  other  part 
of  the  body.  It  appears,  therefore,  that  the  mental  rejDresentation 
of  the  magnitude  of  the  distance  between  two  impressions  varies  in 
inverse  proportion  to  the  real  magnitude  of  the  smallest  perceiv- 
able distance,  on  any  given  area  of  the  skin.  The  same  principle 
holds  good  when  all  the  space  between  the  impressions  is  filled  up, 
as  it  were,  so  as  to  make  a  continuum  of  localized  sensations.  Thus 
Weber  found  that  the  circular  form  of  a  tube  of  only  1^  Parisian 
line  in  diameter  could  be  recognized  by  pressure  on  the  tip  of  the 
tongue  ;  while  on  the  skin  of  the  abdomen  the  diameter  of  the  tube 
must  x'each  3f  inch  before  its  form  was  recognizable.  Our  estimate 
of  the  length  of  lines  of  pressure  marked  out  by  laying  rods  upon 
the  skin  follows  the  same  principle. 

§  22.    Other   important   discoveries   as   to   the   skin's    so-called 


NATURE   OF    SENSATIOIST-CIRCLES.  407 

"  sense  of  locality  "  have  been  made  since  those  of  Weber.  Valen- 
tin has  called  attention  to  the  fact  that  enormous  individual  differ- 
ences exist  in  the  fineness  of  this  kind  of  perception  ;  some  per- 
sons are  not  more  than  one-fourth  as  sensitive  as  are  some  others. 
The  relative  degree  of  fineness  belonging  to  different  areas  of  the 
skin  remains,  however,  approximately  the  same  in  different  persons. 
A.  "W.  Volkmann  '  showed  the  remarkable  effect  of  exercise  upon  the 
cultivation  of  the  sense  of  locality.  After  fixing  the  value  of  the 
least  perceivable  differences  of  locality  for  a  number  of  small  areas 
in  the  field  of  touch,  Volkmann  found  that  each  successive  series  of 
experiments  with  each  area  increased  its  fineness  of  perception, 
until  within  a  few  hours  twice  the  original  degree  of  fineness  could 
be  reached.  The  growth  in  perceptive  skill  of  the  skin  was  slower 
at  first  for  areas  not  ordinarily  used  for  touch ;  quicker  for  those 
accustomed  to  daily  use.  The  improvement  ceased  at  a  certain 
limit,  and  was  soon  lost  by  disuse,  so  that  a  few  months  out  of 
practice  served  to  reduce  the  acquired  tact  of  any  area  to  its  origi- 
nal condition.  A  most  surprising  discovery  of  this  experimenter 
was,  that  the  practice  exclusively  of  a  member  of  the  body  on  one 
side  resulted  in  improving  the  fineness  of  touch  of  the  correspond- 
ing member  of  the  other  side.  Thus,  if  the  smallest  perceivable 
distance  for  the  tip  of  a  left  finger  was,  to  begin  with,  0.75  line, 
and  that  of  the  corresponding  place  on  the  right  finger,  0.85,  prac- 
tice with  the  left  finger  exclusively  reduced  the  distance  for  both 
fingers — for  the  left  to  0.45  line,  and  for  the  right  to  0.4. 

It  is  well  known  that  the  blind,  who  have  no  spatial  series  of 
sensations  or  presentations  of  extended  objects  by  the  eye,  attain  by 
exercise  a  high  degree  of  fineness  for  certain  space-perceptions  of 
the  skin.^  In  the  case  of  those  who  have  sight,  the  most  movable 
and  discriminating  organs  of  the  skin — such  as  the  tips  of  the  fin- , 
gers — are  capable  of  being  cultivated  to  great  delicacy  of  touch  ; 
but  Funke  ^  did  not  succeed,  even  by  an  education  lasting  an  en- 
tire month,  in  reducing  the  obtuseness  of  the  skin  of  the  back  be- 
tween the  shoulder-blades  and  in  the  lumbar  region  more  than  by 
about  one-fourth. 

§  23.  The  explanation  of  Weber's  "  sensation-circles  "  of  the  skin 
has  been  the  subject  of  much  debate.  It  is  natural  at  first  to  as- 
sume that  each  entire  circle  is  provided  with  one  and  only  one 
nerve-fibre,  whose  terminal  expansion  covers  the  circle,  and  whose 
excitation  is  represented  in  consciousness  by  a  sensation  of  a  spe- 

'  Berichte  d.  Sachsischen  Gesellschaft  d.  Wissenschaften,  1858,  p.  38  f. 
'^  Comp.  Czermak,  Sitzgsber.  d.  Wiener  Acad.,  XVII.,  Abth.  ii.,  p.  563  f. 
**  See  Hermauu's  Haudb.  d.  Physiol.,  III.,  ii.,  p.  383. 


408  THE   FIELD    OF   TOUCH. 

cific  value.  Doubtless  certain  anatomical  differences  in  the  nerve- 
fibres  of  tlie  skin,  and  certain  corresponding  physiological  differ- 
ences in  their  function,  must  be  assumed  as  the  basis  of  every  the- 
ory to  account  for  the  skin's  sense  of  locality.  But  Goldscheider's 
experiments  show  that  a  number  of  pressure-spots  must  be  recog- 
nized within  each  sensation-circle,  and  each  pressure-spot  at  least 
should  have  a  sensory  fibre.  Moreover,  every  point  within  each 
sensation-circle  is  itself  sensitive  (however  large  the  circle  may  be), 
and  the  limits  of  none  of  the  circles  are  fixed  as  would  be  the  ex- 
panse of  a  single  nerve-fibre  distributed  over  them.  Still  further, 
different  individuals  differ  greatly  in  the  size  of  these  circles  (and 
we  cannot  well  suppose  a  corresponding  difference  in  the  number 
of  sensory  nerves  of  the  skin),  and  practice  suddenly  and  greatly 
diminishes  the  area  covered  by  a  single  circle.  It  must  at  least  be 
admitted  that  "  the  smallest  perceivable  distance  is  not  a  direct 
measure  for  the  diameter  of  the  sensation-circle."  ' 

Weber  himself  assumed  that  sensation-circles  always  contain  a 
number  of  isolated  nerve-fibres  ;  and  that,  in  order  to  have  the  im- 
pression of  two  localized  sensations,  several  unexcited  fibres  must 
exist  between  the  two  excited.  The  number  of  these  unexcited  fibres 
serves  the  mind  as  a  kind  of  means  for  the  approximate  measure- 
ment of  distances  on  the  skin.  Other  advocates  of  Weber's  ex- 
planation have  spoken  as  though  the  brain  could  somehow  become 
conscious  of  the  unexcited  fibres  lying  between  the  two  excited 
ones,  and  so  derive  a  support  for  its  judgment  from  their  num- 
ber.'' Of  course,  all  attempts  to  explanation  which  assume  the 
mind's  knowledge  of  the  condition  of  the  minute  subdivisions  of 
the  nervous  elements  are  AvhoUy  futile  and  illusory.  Wundt  ^  cor- 
rectly calls  attention  to  the  fact  that  the  diflerences  in  the  so-called 
sensation-circles  of  the  skin  are  simply  a  special  case  under  the 
general  jjsychological  laws  of  the  least  observable  differences  in 
sensations  ;  only  in  this  case  the  differences  are  not  pure  differences 
in  intensity,  but  rather  differences  in  the  complex  color-tone  of  the 
quality  of  sensation.  In  other  words,  the  sensation-circles  represent 
the  local  difference  between  the  points  at  which  stimulus  must  be 
applied  to  the  skin  in  order  to  produce  enough  of  difference  in  the 
color-tone  of  the  resulting  sensations  to  make  them  observable  by 
the  mind.  These  local  signs  of  the  skin,  as  the  organ  of  touch 
proper,  like  all  local  signs,  are  complex  mixtures  of  feeling  belong- 
ing to  different  localities  ;  as  such  they  are  dependent,  not  only 

'  So  Funke,  in  Hermann's  Handb.  d.  Physiol.,  HI.,  ii.,  p.  392  f. 

^  Comp.  Bernstein,  The  Five  Senses  of  Man,  p.  31  f.    New  York,  1876. 

^  Physiolog.  Psychologie,  ii  ,  p.  10. 


THE   THEORY   OF   VIERORDT.  409 

upon  original,  anatomical,  and  physiological  diflferences,  but  also 
upon  other  peculiarities  of  the  individual,  upon  habit,  and  upon 
association  with  each  other  and  with  other  spatial  series  of  sensa- 
tions of  the  skin. 

§  24.  Difficulty  has  been  found  in  assigning  a  conclusive  reason 
why  the  different  areas  of  the  skin  should  differ  so  greatly  in  the 
fineness  of  their  capacity  for  making  local  distinctions.  In  the  view 
of  Lotze,'  this  difference  is  chiefly  due  to  the  varying  character  of 
the  areas  of  the  skin,  with  respect  to  richness  in  nerve-fibres,  thick- 
ness and  so  sensitiveness,  support  and  tension  according  as  the 
skin  is  stretched  over  underlying  soft  or  hard  parts — fat,  muscle, 
tendon,  bone,  etc.  Doubtless  all  such  influences  enter  into  the 
determination  of  that  mixture  of  feeling  which  characterizes  the  lo- 
cal signs  of  the  skin.  The  theory  suggested  by  Vierordt,^  on  the 
basis  of  experiments  made  by  himself  and  his  pupils,  should  also 
be  mentioned.  This  investigator  concluded  that  the  fineness  of 
the  sense  of  locality  belonging  to  any  area  of  the  skin  increases 
in  direct  proportion  with  the  distance  of  that  area  from  the  axes 
about  which  it  is  rotated.  The  relative  fineness  of  the  organ's  local 
sense  is  a  function  of  its  mobility.  Thus  an  uninterrupted  increase 
of  the  power  of  localization  exists  in  the  arm  from  the  acromion 
to  the  tips  of  the  fingers  ;  an  increase  of  its  movableness,  on  the 
whole,  also  exists.  If  a  value  of  100  be  assigned  to  the  power  of 
discrimination  exercised  at  the  acromion,  151  will  represent  that  of 
the  upper  arm,  272  that  of  the  lower  arm,  659  of  the  hand,  2,417 
of  the  thumb,  and  2,582  of  the  tips  of  the  fingers.  In  estimating 
the  relative  movableness  of  these  different  pai-ts,  it  should  be  re- 
membered that  they  not  only  all  move  in  an  enlarging  circuit  from 
the  shoulder- joint  downward,  but  that  each  of  them  from  the  el- 
bow-joint downward  has  its  special  increased  circuit  and  more 
numerous  forms  of  motion. 

But  even  if  Vierordt's  law  could  be  strictly  demonstrated  for 
every  portion  of  the  body,  its  meaning  would  have  to  be  translated 
into  other  terms  in  order  to  be  of  any  real  service  to  psychology. 
It  is  therefore  suggested  by  Fuuke  ^  that  the  increased  power  of 
discrimination  which  belongs  to  the  more  movable  areas  of  the 
skin  is  really  due  to  the  superior  facility  which  they  thus  have  for 
exercise  ;  it  therefore  falls  under  the  law  of  habit.  Furthermore 
— as  we  have  occasion  to  remark  concerning  many  similar  functions 

'  See  Medicin.'Psychologie,  p.  405  f. 

2  Pfluger's  Archiv,  1869,  ii.,  pp.  297  ff.  ;  and  Zeitsclir.  f.  Biologie,  VI.,  VII., 
IX,X.,XL 

"  Hermann's  Handb.  d.  Physiol. ,  III  ,  ii  ,  p.  384. 


410  THE   FIELD    OF   TOUCH. 

of  the  mind  in  correlation  with  the  nervous  mechanism — -the  effect 
of  acquired  habit  is  not  Hmited  to  the  experience  of  the  individual ; 
it  belongs  also  to  the  race.  The  superior  fineness  of  local  sense  in 
some  parts  of  the  body  may  therefore  be  regarded  as  largely  na- 
tive to  the  individual. 

§  25.  The  view  which  must  be  taken  of  Weber's  "  sensation-cir- 
cles," and  of  the  entire  subject  of  the  localization  of  areas  of  press- 
ure on  the  skin,  has  been  largely  changed  by  the  recent  experi- 
ments of  Goldscheider '  and  others.  "We  have  already  seen  (p. 
346  f.)  that  this  experimenter  distinguishes,  more  carefully  than  has 
hitherto  been  done,  the  sensations  of  pressure  from  other  closely 
allied  sensations  coming  through  the  same  organ.  The  finest  point, 
when  it  touches  a  "  pressure-spot,"  produces  a  sensation  of  pressure, 
and  not  one  of  being  pricked  ;  but  touching  other  spots  does  not 
produce  a  sensation  of  pressure  at  all.  It  must  be  held,  then,  that 
the  sensations  produced  by  laying  a  single  blunted  dividers'  point 
upon  the  skin,  as  in  Weber's  classical  experiment,  are  really  very 
complex,  and  are  composed  of  the  sensations  from  several  pressure- 
spots  blended  with  other  sensations  from  the  rest  of  the  same  area 
not  covered  by  the  pressure-spots.  The  fineness  of  discrimination 
possible  in  any  area  of  the  skin  depends,  then,  upon  how  all  the 
points  irritated  stand  related  to  the  specific  pressure-spots.  Gold- 
scheider finds  that  only  when  two  irritating  points  touch  two  press- 
ure-spots are  thej/elt  as  two.  But  when  one  of  the  points  touches 
a  pressure-spot,  and  the  other  touches  some  place  in  the  contiguous 
area  of  skin  which  is  free  from  such  spots,  the  two  points  are  not 
both  felt ;  in  this  case  only  the  one  resting  on  the  pressure-spot  is 
felt. 

Moreover,  the  impression  of  being  doubly  touched  may  be  ex- 
cited by  the  points  when  lying  much  nearer  together,  in  case  they 
rest  upon  pressure-spots  that  belong  to  two  different  chains  of 
such  spots  than  when  both  spots  belong  to  the  same  chain.  This 
is  to  say,  pressure-spots  thus  located  have  a  high  degree  of  sensitive- 
ness. Still  further,  the  minimum  distance  required  to  produce  a 
sensation  of  being  touched  twice  is  surprisingly  small,  when  one  of 
the  touching  points  rests  upon  a  pressure-spot  from  which  the 
chain  radiates  or  at  which  it  makes  a  sharp  bend. 

The  table  of  minimum  distances  at  which  two  points  can  be  felt 
as  two,  when  the  exact  nature  of  the  area  of  the  skin  on  which  we 
are  experimenting  is  known,  and  everything  made  as  favorable  as 

'  On  this  subject,  see  Goldscheider,  Archiv  f.  Aiiat.  u.  Physiol.,  Physiolog 
Abth.,  IbbS,  Supplemeut-Band,  pp.  1-104;  especially,  p.  84  f. 


DIRECTION   OF   THE  PRESSURE-SPOTS. 


411 


possible,  consists  of  numbers  very  much  reduced  from  those  oi 
Weber.     Following?  are  some  citations  from  Goldscheider's  table  : 


Part  of  the  bodj\  mm. 

Back 4-6 

Breast 0.8 

Forehead 0.5-1.0 

Cheek 0.4-0.6 

Nose  and  chin 0.3 

Upper  and  lower  arm 0  5-1.0 


Part  of  the  body.  mm. 

Back  of  hand   0.3-0.6 

I.  and  II.  phalanges  (volar). .  0.2-0.4 
I.  and  II.  phalanges  (dorsal)..  0.4-0.8 

Upper  leg 3.0 

Lower  leg 0.8-2.0 

Back,  and  sole  of  foot 0.8-1.0 


From  the  foregoing  data  it  would  seem  to  follow  that,  as  the  con- 
struction and  relation  of  the  chains  of  pressure-spots  differ  in  the 
different  areas  of  the  body,  so  will  our  sense  of  locality  change. 
The  number,  sensitiveness,  and  direction  in  the  chains  of  these 
spots  determine  the  sensitiveness  of  a  given  area.  Moreover,  our 
perception  of  the  size  and  shape  of  objects  in  contact  with  the  skin 
depends  upon  the  same  conditions.  This  can  be  shown  in  an  as- 
tonishing way  by  comparing  the  apparent  direction  which  the  out- 
lines of  any  small  body  moved  across  the  skin  seem  to  assume  with 
the  way  the  pressure-spots  are  located  in  the  different  areas  through 
which  it  is  moved.  If  the  curve  of  the  chain  of  pressure-spots,  for 
example,  bends  in  the  reverse  direction  from  that  of  the  outline  of 
the  body  moved,  the  effect  may  be  to  make  this  outline  curve  ir- 
regularly or  even  straighten  it  out. 

It  need  scarcely  be  said  that  Goldscheider  regards  the  true  ex- 
planation of  these  phenomena  to  lie  in  the  anatomical  distribution  of 
the  specific  nerves  of  sense  in  the  different  areas  of  the  skin.  How- 
ever this  may  be,  it  is  certain  that  our  sensations  of  pressure  are 
primarily  "punctiform,"  and  afterward  massed  into  a  tactual  continue 
um  ;  and  that  what  we  primarily  know  is  not  the  extended  object  aa 
such,  but  our  sensations  of  pressure  which  are  afterward  objectified. 

§  26.  Closely  connected  with  the  foregoing  is  the  difference  in 
power  of  different  parts  of  the  skin  in  giving  to  the  mind  data  for 
discriminating  the  fact,  the  amount,  and  the  direction  of  motion 
in  contact  with  the  body.  Upon  this  point  the  experiments  of  G. 
Stanley  Hall '  are  of  special  interest.  These  experiments  seem  to 
show  that  we  are  more  likely,  when  in  doubt,  to  judge  motion  on 
the  surface  of  the  limbs  to  be  up  rather  than  down  their  axis  ;  on 
the  breast,  the  shoulder-blades,  and  the  back,  the  tendency  is  to 
judge  motion  to  be  toward  the  head.  The  discriminative  sensi- 
bility of  the  skin  for  motion  is  much  greater  than  that  for  sepa- 
rate touch,  as  determined  by  Weber's  experiments.     Thus,  while  at 


'  Motor   Sensations   on  the  Skin,  by   Professor  G.  S.  Hall   and  Dr.    H.  H 
Donaldson,  in  Mind,  October,  1885,  pp.  557  ff. 


412  THE   FIELD    OF   TOUCH. 

least  a  distance  of  25  mm.  between  the  dividers*  points  was  needed 
on  the  volar  surface  of  the  right  arm,  in  order  to  perceive  them 
as  two  points,  both  the  fact  and  the  direction  of  motion  could  be 
discriminated  at  an  average  distance  of  between  6  and  7  mm.  In 
judging  the  rate  and  distance  of  motion  over  the  skin  the  liabil- 
ity to  error  is  always  great ;  but,  as  a  rule,  distances  rapidly  trav- 
ersed are  judged  to  be  relatively  shorter  than  the  same  distances 
more  slowly  traversed.  Inasmuch,  however,  as  the  judgment  of 
motion  on  the  left  arm  was  expressed  by  reproducing  the  rate 
and  distance  with  the  right  hand,'  we  have  a  double  liability  to 
en'or  involved  in  regulating  the  muscular  movenient  of  this  hand 
by  means  of  its  series  of  muscular  and  tactual  sensations. 

Hall  found  the  motor  sensibility  of  different  parts  of  the  surface 
of  the  skin  to  be  different ;  but  the  differences  do  not  appear  to 
correspond  to  those  belonging  to  Weber's  sensation -circles.  The 
average  distance,  in  millimeters,  which  a  metallic  point  of  12  mm. 
in  diameter  could  move  over  the  skin  at  a  rate  of  2  mm.  per  second 
before  a  judgment  of  direction  could  be  formed  was  found,  for  one 
subject  of  experiment,  as  follow^s  :  forehead,  0.20;  upper  arm,  0.40; 
forearm,  0.44  ;  shin,  0.60;  palm,  0.74;  back,  0.85.  Motion  can  be 
produced  so  slowly  as  not  to  be  discriminated  at  all,  even  when  the 
body  in  contact  has  really  moved  from  6  to  12  centimeters.  It  can 
also  be  jjroduced  so  rapidly  as  to  make  it  impossible  to  tell  when  it 
begins  and  when  ends.  Heavy  weights  seem  to  move  faster  than 
light  ones  going  at  the  same  rate  ;  but  here  other  sensations  are 
called  out  by  the  deep  pressure,  and  combined  with  those  of  con- 
tact. Hall  concludes  that  heat-spots  and  cold-sjjots  traversed  by 
the  moving  body  are  of  great  service  in  judging  motion  and  its  di- 
rection on  the  skin  ;  the  cold-spots  more  than  the  heat  spots,  "be- 
cause of  the  fainter  sensation  and  wider  irradiation  "  of  the  latter. 

Further  experiments  with  a  travelling  metallic  point  that  carried 
the  stimulus  of  an  electrical  current  over  the  surface  of  the  skin 
showed  an  astonishing  diversity  of  sensations  developed  at  different 
points  of  the  area  thus  traversed.  Points  of  cutting  pain,  "  thrill- 
points,"  "tickle-points,"  "  acceleration-points  "  (or  places  where  the 
rate  of  motion  seems  suddenly  to  increase  without  any  real  change 
in  the  speed  of  the  moving  metal),  "  blind-points  "  (or  spots  where 
all  impression  of  contact  is  momentarily  lost),  are  all  to  be  differen- 
tiated. Yet  the  sharp  differentiation  of  these  sensations  is  ren- 
dered difficult  by  the  fact  that  the  various  kinds  are  so  impacted 
and  run  together,  in  a  tayigle  of  sensation.  The  experimenters  also 
speak  as  though  many  dermal  sensations  may  thus  be  j)artially  dis- 
'  Mind,  October,  1885,  p.  564  f. 


nXEXSSS    OF   TZ.UPEI^iTUnE-GENSE. 


413 


entangled,  for  the  description  of  whicli  language  furnishes  no  ade- 
quate terms.  All  these  facts  agree  exceedingly  well  with  the  theory 
of  local  signs  already  proposed.  These  dermal  signs  are  complex 
"mixtures"  of  feeling,  which  give  to  each  discernible  locahty  a 
characteristic  local  stamp.  The  fact  that  our  sensibility  to  motion 
is  so  much  greater  in  each  area  of  the  skin  than  our  susceptibility 
to  the  distance  of  stationary  points  accords  with  the  same  theory. 
Our  ability  to  localize  the  dermal  sensations  is  dependent  upon  the 
degree  and  rate  of  the  changes  in  the  color-tone  of  these  sensations. 
Hall  is  undoubtedly  right  in  holding  that,  by  moving  the  touching- 
surface  over  the  surface  touched,  we  do  not  simply  multiply,  but 
also  diversify,  our  data  for  filling  up  the  dermal  blind-spots  and 
judging  the  nature  of  impressions. 

§  27.  The  localizing  of  sensations  of  temperature  in  the  skin  is, 
in  principle,  the  same  as  that  of  sensations  of  light-pressure  or  of 
motion.  The  former,  however,  are  in  all  our  ordinary  experience 
interwoven  with'  the  latter  ;  they  therefore  have  the  helj)  of  the  lat- 
ter in  getting  a  place  assigned  to  them  in  the  periphery  of  the 
body.  Kecent  researches,  already  referred  to  (Chap.  IV.,  §  22),  dem- 
onstrate the  fact  that  the  relative  number  and  arrangement  of 
heat-spots  and  cold-spots  is  different  for  different  areas  of  the  skin. 
Goldscheider  '  has  experimented  to  determine  how  far  apart  the 
heat-spots  and  cold-spots  must  be,  respectively,  in  order  that  two 
of  them,  when  stimulated,  may  he  felt  as  two.  Both  kinds  of  sen- 
sations are  localized,  not  as  points,  but  as  minute  warm  or  cold 
drops  in  contact  with  the  skin.  By  the  following  table,  which 
gives  the  minimum  distances  for  different  areas  of  the  body,  it  ap- 
pears that  the  sense  of  locality  connected  with  the  cold-spots  is 
about  twice  as  fine,  as  a  rule,  as  that  connected  with  the  heat-spots. 
The  distances  are  given  in  millimeters. 


Part  of  the  body. 

Cold-spots. 

Heat-spots. 

Foreliead    clieek,  and  cliin       

0.8 

2.0 

1-2 
1.5-2.0 
1.5-2.0 

2-3 

0.8 

2-3 

3-5 

Breast       

4-5 

Abdomen 

4-6 

Back                

4-6 

Upper  arm 

2-3 

Lower  arm     .          

2-3 

Hollow  of  the  hand           .                  

2.0 

3-4 

'  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth.,  1885,  Supplement-Band,  pp. 
70  fE. 


414  THE   FIELD   OF  TOUCH. 

Some  basis  seems  to  be  laid  in  the  foregoing  facts  for  a  system 
of  local  signs  of  the  skin,  that  consist  in  a  mixture  of  color-tones  of 
temperature-sensations.  Yet  sensations  of  heat  or  cold,  in  them- 
selves considered,  differ  chiefly,  if  not  wholly,  in  intensity.  In  them- 
selves, therefore,  they  are  not  well  fitted  to  constitute  a  so-called 
"  spatial  series  "  of  sensations.  If,  for  example,  a  certain  area  of 
the  skin  be  stimulated  simultaneously  by  both  heat  and  cold,  at 
points  too  near  together  to  be  distinguished  by  touch,  the  result  is 
neither  a  modification  of  one  sensation  by  the  other  nor  a  localizing 
of  the  two  sensations  as  Ij'ing  closely  side  by  side.'  A  wavering  of 
perception  rather  takes  place,  similar  to  the  strife  of  colors  in  vi- 
sion ;  the  experience  is  as  though  the  skin  were  being  touched  with 
a  single  body  alternately  hot  and  cold.  Klug  also  found  that  the 
least  observable  distance  between  two  points  touching  the  skin  at 
the  same  time  depends  upon  their  temperature  relative  to  that  of 
the  skin.  The  medium  value  of  this  distance  "is  reached  when  these 
points  have  a  temperature  of  20°-40°  C.  (68^-104°  Fahr.) ;  it  dimin- 
ishes on  either  raising  or  depressing  their  temperature  greatly 
above  or  below  the  zero-point  of  the  skin.  The  fineness  of  our 
sense  of  locality,  as  well  as  of  our  sensitiveness  to  motion  (comp. 
§  25),  is  increased  by  exciting  sensations  of  temperature  up  to  the 
point  where  pain  intervenes.  But  the  localizing  of  these  sensations 
is  primarily  dependent,  to  a  great  extent,  uj)on  their  connection 
with  localized  sensations  of  touch.  If  we  bring  two  parts  of  the 
skin,  that  differ  considerably  in  temperature,  into  contact — for  ex- 
ample, a  cool  hand  and  warm  forehead,  or  a  cool  hand  and  a  warm 
one — it  is  often  difficult  by  strict  attention  to  the  sensations  of  tem- 
]Derature  -alone  to  tell  which  part  is  cooler,  which  warmer.  The 
difficulty  is  doubtless  largely  due  to  the  fact  that  each  part  which 
feels  the  temperature  of  the  other  is  also  changing  its  own  tem- 
perature in  the  direction  of  the  temperature  of  the  othei\  It  is 
therefore  induced  to  feel  itself,  as  it  were,  as  being  of  the  tempera- 
ture of  that  other,  A  confusion  of  the  data  for  judgment,  accord- 
ingly, takes  place.  Any  localization  of  the  sensations  which  occurs 
under  such  circumstances  is  largely  dependent  upon  secondary  con- 
siderations, and  especially  upon  the  direction  of  the  attention. 

We  judge  of  depth  by  sensations  of  temperature,  indirectly,  and 
through  our  ability  to  remove  or  change  the  intensity  and  locality 
of  these  sensations  by  changing  the  position  of  the  body  in  space 
as  related  to  what  we  know  to  be  hot  and  cold  bodies  or  surround- 
ing media. 

'  See  Czermak,  Sitzgsber.  d.  Wiener  Acad.,  March,  1855,  p.  500;  confirmed 
by  Klug  and  otliers. 


ISTATUKE   OP  THE   MUSCULAR  SEISTSE.  415 

§  28.  The  specific  sensations  of  the  muscular  sense  constitute 
another  spatial  series  which  combines  with  the  foregoing  in  the 
localizing  of  areas  at  the  periphery,  and  of  external  objects  as 
projected  in  space  and  yet  known  as  in  contact  with  the  body.  In- 
deed, it  is  upon  this  particular  system  of  local  signs  that  the  mind 
is  chiefly  dependent  for  its  data — other  than  the  visual — in  the 
synthetic  construction  of  its  presentations  of  bodies  that  stand  re- 
lated to  each  other  in  three  dimensions  in  objective  space.  Three 
principal  theories  have  been  held  as  to  the  nature  of  the  so-called 
muscular  sensations :  (1)  So  far  as  they  are  not  tactual,  they  are  to 
be  resolved  into  "  central  feelings  of  innervation,"  which  differ  only 
in  intensity  and  not  in  specific  quality,  and  which  result  from  the 
changes,  initiating  movement  of  the  bodily  organs,  that  take  place 
in  the  brain  as  correlated  with  impulses  of  the  will  (so  Wundt,  and 
others)  ;  (2)  they  are  not  specific  sensations,  but  are  due  to  interpre- 
tations of  those  feelings  in  the  skin  which  originate  on  account  of 
its  changes  of  position,  tension,  etc.,  as  the  underlying  muscles  are 
moved  (so  Schiff,  and  others) ;  (3)  they  are  specific  sensations  de- 
pendent on  a  specific  nerve-apparatus  of  sense,  which  has  its  end^ 
organs  in  the  muscle-fibre,  and  which  is  excited  by  the  contraction 
of  the  latter  in  a  manner  dependent  upon  the  kind,  ainount,  and 
direction  of  the  muscular  movement  taking  place  (so  Bell,  Weber, 
Funke,  and  others). 

We  have  already  given  certain  reasons  for  rejecting  the  first 
two  and  accepting  the  last  of  the  foregoing  views  (see  p.  344  f.) ; 
other  reasons  will  be  mentioned  subsequently  in  discussing  the 
so-called  "feeling  of  innervation"  or  of  "active  energy."  The 
muscular  sense,  like  all  the  other  senses  which  contribute  to  our 
presentations  of  objects  extended  in  space,  appears  to  have  its  own 
system  of  local  signs.  The  muscular  sensations  are  qualitatively 
(and  not  merely  quantitatively)  different,  according  to  the  combi- 
nation of  the  muscles  moved,  and  according  to  the  extension  over 
the  muscular  area  of  the  stimulus  imparted  to  the  sensory  nerve- 
fibres  situated  in  the  muscle  by  the  changing  condition  of  the 
latter  as  it  contracts  and  relaxes.  The  series  of  sensations — with 
all  the  qualities  of  rapid  and  nice  gradations  which  belong  to 
"spatial  series"  of  sensations — called  out  by  moving  one  limb  dif- 
fers from  that  called  out  by  moving  another  limb.  At  each  step  in 
the  flexing  of  the  leg — for  example — the  color-tone  of  the  muscular 
sensations  has  a  specific  quality  and  value  as  a  local  sign,  in  our 
consciousness,  of  the  position  of  the  member.  The  same  thing  is 
true  of  the  bending  arm,  back,  or  single  toe  or  finger.  These  sen- 
sations are  intimately,  and  even  inextricably,  combined  with  the 


416  THE    FIELD    OF    TOUCH. 

spatial  series  of  specifically  dermal  sensations  ;  but  in  themselves 
tliey  have  a  different  quality,  and  ai-e  not  localized  simply  at  the 
surface  of  the  body.  As  the  extent  of  the  circuit  of  motion  gone 
through  by  any  limb  increases,  or  the  intensity  of  the  strain  be- 
comes greater,  the  quality  of  the  mass  of  resulting  muscular  sensa- 
tions is  perpetually  changing.  These  sensations  are,  accordingly, 
localized  over  a  broader  area  of  the  body  and  deeper  in  its  sub- 
stance, as  it  were.  Everyone  knows  what  new  mixtures  of  sensa- 
tion are  produced  in  consciousness  by  calling  into  vigorous  exer- 
cise the  unused  more  deeply  lying  muscles  of  the  body.  Bain'  has 
discussed  these  sensations  at  great  length  and  with  commenda- 
ble acuteness.  But  the  apparent  assumption  that  these  particu- 
lar sensations  can,  by  being  associated,  acquire  of  themselves  the 
quality  of  extension  in  space,  and  the  accounting  for  all  our  other 
perceptions  of  sjDatial  qualities  and  relations  as  merely  secondary 
and  symbolic  of  the  associated  muscular  sensations,  are  in  plain 
contradiction  of  established  psychological  facts  and  principles. 

The  muscular  sensations  also  assist  the  more  strictly  tactual  in 
discriminating  locality  for  all  cases  where  the  pressure  upon  the 
sliin  exceeds  a  certain  small  degree  of  intensity.  In  strong  contact 
or  heavy  pressure  the  sensory  nerves  of  the  underlying  muscle  are 
excited;  we  have  the  feeling,  not  simply  of  being  touched,  but  also 
of  being  pressed.  The  combination  of  these  two  spatial  series 
gives  to  the  mind  a  doubly  constituted  system  of  local  signs ;  hence, 
as  the  experiments  of  G.  Stanley  Hall  ^  show,  our  judgment  of  di- 
rection of  motion  is  quicker  as  the  weight  resting  on  the  skin  is 
increased  np  to  the  limit  where  other  disturbing  sensations  inter- 
vene. The  superior  discriminating  power  which  any  member  of 
the  body  has  when  permitted  to  move — that  is,  to  call  forth  fa- 
miliar series  of  muscular  sensations — is  largely  due  to  the  help 
which  the  local  signs  of  this  system  render  to  the  mind.  When 
the  particular  member  (the  hand)  which  is  capable  of  the  nicest 
tactual  discrimination  is  also  permitted  to  move  over  an  object 
freely,  and  to  acquire  abundant  data  from  all  the  sources  described 
above,  we  have  fulfilled  the  most  advantageous  conditions  for  the 
utmost  nicety  of  knowledge  possible  to  "  touch,"  in  the  widest 
meaning  of  the  word. 

§  29.  It  is  unnecessary  to  illustrate  in  further  detail  the  process 
by  which  the  mind,  with  its  native  synthetic  activity,  and  with 
the  help  of  qualitatively  different  sensations,  constructs  its  field  of 

'  The  Senses  and  the  Intellect,  especially  pp.  57-100,  336-348,  and  364- 
398. 

2  Mind,  October,  1885,  p.  567. 


TOUCHIlSrG   AND   BEIISTG  TOUCHED.  401 

tions  are  localized  ;  we  see  some  of  the  same  parts  as  projected  in 
space  before  our  eyes.  Objects  that  are  not  a  part  of  ourselves  are 
given  to  us  as  projected  eccentrically,  either  by  touch  through  their 
being  in  contact  with  the  skin  and  occasioning  sensations  of  mus- 
cular exertion,  or  by  sight  as  having  distance  in  its  field  of  vision. 
Localization  and  projection  are  not  to  be  regarded  as  two  phases  of 
one  and  the  same  process  ;  we  do  not  first  have  the  presentations 
of  sense  as  pai'ts  of  the  periphery  of  our  bodies,  and  then,  on  further 
experience,  push  them  beyond  this  periphery,  either  to  an  infini- 
tesimal distance  or  to  one  remote.  Localization  and  eccentric  pro- 
jection are  rather  two  processes,  largely  unlike,  which  go  on  con- 
temporaneously and  are  set  up  chiefly  on  the  basis  of  different 
classes  of  sensations. 

Where  two  parts  of  the  sensitive  skin  of  our  own  bodies  come 
together  the  conditions  for  both  of  the  above-mentioned  processes 
are  fulfilled.  Accordingly,  one  part  has  localized  in  it  those  com- 
plex sensations  which  make  us  aware  that  this  part  of  our  body  is 
touching  something  ;  the  other  has  localized  in  it  those  sensations 
which  make  us  aware  that  this  part  is  being  toadied  by  something. 
Which  of  the  two  parts  shall  be  regarded  as  touching,  and  which  as 
being  touched,  depends  on  various  considerations.  Those  mem- 
bers of  the  body  which  are  most  used  in  active  touch  are  generally 
known  as  touching,  and  the  less  active  parts  as  being  touched.  For 
example,  if  -with  closed  eyes  the  forehead  be  moved  across  the  sta- 
tionary tip  of  a  finger,  the  latter  will  appear  to  be  the  active  organ 
of  touch.  Comparatively  insensitive  areas  of  the  skin  are  less  likely 
to  be  presented  to  the  mind  as  touching  other  more  sensitive  parts ; 
callous  spots,  indurated  surfaces,  etc.,  seem,  as  a  rule,  to  be  touched. 
Parts  of  the  body  which  lose  all  sensitiveness  come  to  be  regarded 
as  external  things.  If  the  tip  of  a  finger  of  normal  sensitiveness  be 
brought  into  contact  with  the  callous  tip  of  the  corresponding  fin- 
ger of  the  other  hand,  the  former  will  be  known  as  touching  and 
the  latter  as  being  touched.  The  direction  of  attention  often  deter- 
mines the  strife,  as  it  were,  between  the  motifs  to  localization  and 
those  to  eccentric  projection.  We  ordinarily  strive  to  ga,in  knowl- 
edge of  the  qualities  of  some  outside  object,  rather  than  of  the  con- 
dition of  our  own  periphery  with  respect  to  the  sensations  localized 
in  it ;  the  attention  is  therefore  directed  to  those  series  of  sensations 
which  form  the  basis  of  eccentric  projection,  even  when  some  part 
of  our  own  sensitive  organism  is  the  object  known.  But  sensations 
which  are  accompanied  by  obtrusive  feeling  of  some  kind  furnish 
superior  grounds  for  localization.  We  locate  pains,  pricks,  severe 
pressure,  sensations  of  creeping,  and  tickling,  in  the  body.  In  gen- 
26 


402  PEECEPTIOlSrS   OF   THE   LOWEE   SENSES. 

eral,  then,  a  strong  tone  of  feeling  with  the  sensation  favors  the 
process  of  localizing ;  tonelessness  of  sensation  favors  the  process 
of  objectifying.' 

A  system  of  localized  sensations,  gained  chiefly  by  pressure  of 
the  skin  and  muscles,  and  accompanied  by  a  strong  tone  of  feeling, 
gives  us  the  primary  field  of  the  body  as  known  to  touch.  Certain 
points  of  starting,  as  it  were,  must  first  be  fixed  in  the  process  of 
locahzing  ;  this  process  then  goes  on  by  relating  all  other  localized 
sensations  to  these  points  of  starting.  But  by  eccentric  projection, 
the  system  of  muscular  sensations  of  movement  and  the  system  of 
visual  sensations  are  combined  to  develop  our  perceptions  of  ob- 
jective space  with  its  three  dimensions.  The  sensations  of  touch 
are  subsequently  projected  into  a  space  thus  originally  constituted 
by  combined  muscular  sensations  and  visual  sensations.  The  eye 
and  hand  in  motion,  therefore,  project  their  extended  objects  into 
a  space  which  they  develop  themselves  ;  while  the  ear  and  the  nose 
project  their  perceptions  into  a  space  which  they  are  compelled  to 
assume  on  the  authority  of  the  other  senses. 

The  foregoing  principles  must  now  be  illustrated  and  confirmed 
by  a  brief  statement  of  facts  which  relate  to  the  formation  and  de- 
velopment of  presentations  of  sense  by  a  synthesis  of  simple  sen- 
sations. Attention  will,  for  obvious  reasons,  be  directed  almost 
exclusively  to  those  presentations  of  sense  which  come  through  the 
eye  and  skin,  including  in  both  the  influence  of  muscular  sensa- 
tions. 

§  17.  Perceptions  of  Smell  differ  only  in  fineness,  duration,  and  ac- 
companying tone  of  feeling  ;  they  have  no  size  or  shape,  no  spatial 
properties  of  any  kind.  They  cannot  even  be  said  to  be  localized. 
Fineness  of  smell,  or  power  to  make  minute  distinctions  in  quality, 
and  so  infer  the  presence  or  direction  of  an  object  previously  known 
to  excite  such  quality  of  sensations,  differs  greatly  in  different  spe- 
cies of  animals  and  in  different  individuals  of  the  same  species. 
The  exploits  of  some  animals  give  ground  for  the  conjecture  that 
every  species,  and  even  every  individual,  has  an  odor  of  its  own.'^ 
The  direction  and  nature  of  the  object  which  causes  the  sensations 
are  judged  by  variations  of  intensity  on  turning  the  head,  or  on 
approaching  or  receding  from  the  object.  Sensations  of  smell  are 
known  to  come  through  the  nose,  by  localizing  there  the  accom- 

'  Compare  Volkmann  von  Volkmar,  Lehrbuch  der  Psycliologie,  II.,  p. 
126  f. 

■^  See  the  articles  of  Donhoff,  in  Archiv  f.  Anat.,  Physiol.,  etc.,  Physiolog. 
Abth  ,  p.  750  f.  (1874) ;  and  Jiiger,  in  Zeitschr.  f.  wissensch.  Zool.,  xxvii.,  p. 
319  f.  (1876). 


TASTE   AND   HEARING.  403 

panying  muscular  and  tactual  sensations  with  their  strong  tone  of 
feeling.  This  is  readily  done,  since  we  draw  the  air  through  the 
nostrils  and  feel  its  double  effects  in  producing  the  two  classes  of 
sensations.  As  to  the  simultaneous  influence  of  two  smells,  little 
is  known  beyond  the  statement  of  Valentin,  that  the  stronger 
overwhelms  the  weaker.  The  power  of  discrimination  may,  of 
course,  be  cultivated  in  this  sense  as  in  every  other.' 

§  18.  Most  of  the  remarks  just  made  as  to  perceptions  of  smell 
apply  also  to  Perceptions  of  Taste.  Sensations  of  taste,  however,  are 
much  more  closely  connected  with  those  of  touch  ;  since  the  tongue 
is  a  chief  organ  of  active  touch.  It  is  the  tactual  and  muscular 
sensations,  and  not  the  purely  qualitative  affections  of  taste,  which 
are  localized  in  the  mouth.  Concerning  contrast  and  compensation 
of  tastes,  little  is  known  which  does  not  belong  to  ordinary  experi- 
ence. Valentin  ^  alleges  that  when  a  sour  mass  is  laid  on  one  half, 
and  a  bitter  mass  on  the  other  half,  of  the  root  of  the  tongue,  the 
predominating  taste  may  sometimes  be  determined  by  our  choice. 
It  is  well  known  that  certain  tastes  compensate  each  other,  as  it 
were,  in  experience,  without  any  chemical  equivalence  of  their  prop- 
erties. The  sugar  neutralizes  the  acid  of  the  lemonade,  not  in  the 
vessel  that  contains  the  mixture,  but  in  the  nervous  system  of  him 
who  drinks  ih  Briicke  holds  ^  that  the  neutralizing  of  one  sensa- 
tion of  taste  by  the  other  takes  place  in  the  brain.  The  sensation 
of  bitter  is  esj^ecially  difficult  to  cover  or  neutralize. 

§19.  Perceptions  of  Hearing  ne^i  demand  consideration.  More 
difficulty  accompanies  the  effort  to  establish  the  proposition  that 
sensations  of  sound  are  not  directly  localized,  but  are  projected 
in  a  space  constituted  chiefly  by  the  eye  and  the  hand,  through 
complicated  indii'ect  inferences.  Such  a  proposition  is,  however, 
undoubtedly  true.  The  localizing  of  the  area  of  the  body  which 
serves  as  the  organ  of  the  sensations  of  sound,  the  knowledge  that 
we  hear  iDith  the  ear,  is  accomplished  chiefly  through  those  sen- 
sations of  shock  to  the  muscles  and  skin  of  the  region  which  come 
from  loud  and  massive  or  piercing  sounds.  Sensations  of  sound 
originating  through  excitement  within  or  very  near  to  the  ear  itself 
are  called  "  entotic."  A  great  part  of  such  sounds,  if  not  all  of  them, 
are  transmitted  through  the  tympanum.  Perceptions  combined  of 
such  sensations  may  be  located  either  within  the  ear  or  at  some  dis- 

'  On  the  whole  subject  see  von  Vintscligaus  monograph  in  Hermann,  Handb: 
d.  Physiol.,  HI.,  ii.,  pp.  225  ff. 

^  Lehrbuch  der  Physiol,  d.  Menschen,  etc.,  Abth.  ii.,  p.  308  (second  edi- 
tion). 

^  Vorlesungen  ilber  Physiol,  (ed.  1884),  ii.,  p.  263. 


404  PERCEPTIOlSrS    OF   THE   LOWER   SEISTSES. 

tance  from  the  body,  according  to  previous  associations  and  oppor- 
tunities for  judgment.  The  sound  produced  by  the  vibration  of  the 
adjoining  muscles,  and  heard  as  a  low  musical  tone  when  the  fin- 
gers are  pressed  in  the  ears  (especially  if  the  teeth  are  tightly  set 
together),  is  located  in  the  head  by  the  help  of  its  accompanying 
sensations  of  other  kinds.  The  same  thing  is  true  of  the  crackling 
noise  sometimes  produced  by  yawning,  or  of  the  whirring  occasioned 
by  the  passing  of  the  blood  through  the  neighboring  large  blood- 
vessels. In  the  same  way  we  learn  to  hear  the  beating  of  oiir  own 
hearts,  or  the  noise  of  air  in  our  respiration.  But  the  click  of  the 
valves  of  the  internal  organ  may,  when  experience  gained  through 
tactual  and  muscular  sensation  fails  us,  be  located  in  the  watch 
under  our  pillow;  just  as  the  singing  or  ringing  "in  the  ears" 
produced  by  quinine,  or  cerebral  excitement  otherwise  occasioned, 
may  be  located  in  a  cricket  supposed  to  be  upon  the  sill  of  the  open 
window.  In  certain  pathological  cases  the  power  to  distinguish 
between  entotic  sounds  and  those  having  an  external  origin  is  al- 
most  wholh'  lost. 

§  20.  We  can  orientate  ourselves  in  space  with  reference  to  ex- 
ternal sounds  with  great  speed  and  considerable  precision,  but  as 
an  acquired  art  differing  in  different  individuals  and  dependent 
upon  attention  and  previous  experience.  E.  H.  Weber  thought 
that  we  tell  the  direction  of  sounds  by  ihe  help  of  the  feeling  of 
the  swing  of  the  ear-drum  ;  and  instanced,  in  proof,  that  this 
eccentric  projection  is  hindered  by  filling  the  external  jD^ssage 
of  the  ear  with  water.  When  using  both  ears  and  moving  the 
head  freely  in  space,  we  undoubtedly  determine  the  direction  of 
sounds  by  differences  in  the  intensity  of  the  sensation  dependent 
upon  changes  in  the  relative  position  of  both  ears.  Rayleigh ' 
found  that,  in  a  quiet  place  under  favorable  circumstances,  the 
direction  of  a  word  or  letter  uttered  in  a  natural  voice  could  be 
given  with  considerable  accuracy  ;  that  of  a  musical  tone  much 
less  accurately.  The  direction  of  a  sound  from  a  tuning-fork 
could  not  be  given  when  it  was  held  either  behind  or  before,  but 
could  be  given  if  the  fork  was  held  to  the  right  or  to  the  left.  It 
is  said  that  the  conducting  of  an  intermitting  current  from  a  tele- 
phone through  both  ears  causes  a  perception  of  tone  localized  in  the 
median  plane  of  the  head. 

Such  facts  as  the  foregoing  introduce  us  to  the  theory  of  "acous- 
tic shadows,"  or  of  the  amount  of  "  covering  "  power  which  the 
sound  produced  by  the  waves  of  a  given  intensity  entering  one 
ear  would  have  upon  the  sound  produced  by  waves  of  a  different 
'  Nature,  XIV.,  p.  32. 


THE    EXPERIMENTS    OF   WEBER.  405 

intensity  entering  the  other  ear.  It  does  not  appear  to  Hensen,' 
however,  that  the  prompt  and  accui-ate  locaHzatiou  of  direction 
possible  to  some  ears  can  be  wholly  accounted  for  by  the  theory  of 
acoustic  shadows.  Some  other  form  of  feeling,  possibly  connected 
with  the  remarkable  arrangement  of  the  semicircular  canals,  may 
blend  with  the  estimate  of  differences  in  intensity  to  form  a  basis  f or 
judgment.  Von  Kries  and  Auerbach  found  that  the  jDromptness 
with  which  the  direction  of  the  noise  from  an  electric  spark  can  be 
localized  depends  upon  its  relation  to  the  circuit  of  the  head." 

Our  perceptions  of  the  absolute  distance  of  sounding  objects  are 
entirely  dependent  upon  our  knowledge  of  the  quality  and  quantity 
of  the  sounds  ordinarily  proceeding  from  them  ;  they  are,  that  is 
to  say,  not  presentations  of  sense,  but  indirect  estimates  as  to  the 
objective  cause  of  the  sensations  immediately  experienced.  It  has 
been  claimed  that  a  change  in  the  relation  of  the  partial  tones  to 
the  fundamental  tone,  dependent  upon  the  remoteness  of  the  place 
of  origin  of  the  compound  clang,  aids  our  estimate  of  distance  by 
sound. 

§  21.  An  account  of  the  process  by  which  a  Field  of  Touch  is  con- 
structed, and  extended  objects  are  known  as  iu  contact  with  the 
skin  at  definite  points  or  areas  of  it,  must  begin  by  enumerating  the 
data  which  the  mind  has  for  such  activity.  The  most  important  of 
these  data  are  indicated  by  certain  facts  as  to  the  fineness  of  the 
so-called  "  sense  of  locality  "  belonging  to  the  skin.  E.  H.  Weber 
first  estabHshed  a  rule  for  measuring  the  degree  of  this  fineness  ac- 
curately ;  he  also  mapped  out  the  entire  field  of  the  surface  of  the 
body  into  areas  differing  greatly  in  their  fineness.^  For  a  measur- 
ing instrument  he  used  the  two  points  of  a  pair  of  dividers,  blunted 
so  as  to  prevent  the  sensation  of  being  pricked  ;  the  princi^Dle  of 
measurement  was  that  the  minimum  distance  apart  at  which  the 
two  points,  when  touching  the  skin  of  any  region,  are  felt  as  tivo  local- 
ized sensations  is  the  measure  of  the  sensitiveness  to  local  distinction 
of  that  region.  The  following  table  gives  some  of  the  results  of 
Weber's  experiments ;  the  figures  indicate  the  number  of  milli- 
meters *  apart  which  the  points  of  the  dividers  were  when  the  given 
area  of  the  organ  was  just  able  to  distinguish  them  ; 

'  In  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  136. 

2  Archiv  1  Anat.  u.  PliysioL,  Physiolog.  Abth  ,  1877,  p.  331  f. 

^  Annot.  Anatom.,  vii.,  p.  4  f.  ;  Wagner's  Handworterb.  d.  Physiol.,  III., 
Abth   ii.,  p.  529  f. 

^  The  numbers  were  given  by  Weber  in  Parisian  lines ;  in  the  table  they  are 
taken  f rom  Wundt,  Physiolog.  Psychologie,  ii.,  p.  7,  who  has  reduced  them  to 
even  millimeters. 


406  THE   FIELD    OF   TOUCH. 

Tip  of  the  tongue .- 1 

Volar  side  of  the  last  phalanx  of  the  finger   2 

Red  part  of  the  lips 5 

Volar  side  of  the  second  and  dorsal  side  of  the  third  phalanx  of  the  finger  .     7 

White  of  the  lips,  and  metacarpus  of  the  thumb 9 

Cheek,  and  plantar  side  of  the  last  phalanx  of  the  great-toe 11 

Dorsal  side  of  the  first  phalanx  of  the  finger 16 

Skin  on  the  back  part  of  cheek-bone,  and  forehead 23 

Back  of  the  hand 31 

Knee-pan,  and  surrounding  region 36 

Forearm,  lower  leg,  back  of  the  foot  near  the  toes 40 

Skin  of  the  nape,  and  of  the  back  in  the  five  upper  cervical  vertebrae 54 

Skin  of  the  middle  of  the  back,  and  of  the  upper  arm  and  leg 68 

Weber  also  found  that  the  fineness  of  the  sense  of  locality  is 
greater  in  a  transverse  than  in  a  longitudinal  direction,  on  both  arms 
and  legs.  On  these  surfaces  of  the  skin  the  "  sensation-circles,"  or 
areas  within  which  the  minimum  distances  of  the  dividers'  points 
are  felt  as  two  points,  have  an  elliptical  shape,  with  their  long  axes 
up  and  down.  That  the  size  of  the  sensation-circles,  or  the  fineness 
of  the  sense  of  localit}',  largely  forms  the  basis  for  our  judgments 
of  the  position,  number,  and  magnitude  of  the  localized  sensations 
in  the  field  of  touch  may  be  shown  by  a  simple  experiment.  If 
the  points  of  the  dividers  be  separated  somewhat  less  than  is  neces- 
sary in  order  to  distinguish  them  as  two  on  the  cheek  just  in  front 
of  the  ear,  and  then  (the  distance  apart  of  the  points  remaining  un- 
changed) be  slowl}^  moved  until  one  point  rests  upon  the  upper  and 
the  other  upon  the  lower  lip,  to  a  person  blindfold,  and  unpreju- 
diced by  knowing  what  is  to  take  place,  the  point  first  felt  as  one 
will  appear  to  become  two,  and  then  the  two  recede  from  each 
other  continually  as  the  parts  with  a  finer  sense  of  locality  are  trav- 
ersed. The  same  experiment  may  be  tried  upon  any  other  part 
of  the  body.  It  appears,  therefore,  that  the  mental  representation 
of  the  magnitude  of  the  distance  between  two  impressions  varies  in 
inverse  proportion  to  the  real  magnitude  of  the  smallest  perceiv- 
able distance,  on  any  given  area  of  the  skin.  The  same  principle 
holds  good  when  all  the  space  between  the  impressions  is  filled  up, 
as  it  were,  so  as  to  make  a  continuum  of  localized  sensations.  Thus 
Weber  found  that  the  circular  form  of  a  tube  of  only  It}  Parisian 
line  in  diameter  could  be  recognized  by  pressure  on  the  tip  of  the 
tongue  ;  while  on  the  skin  of  the  abdomen  the  diameter  of  the  tube 
must  reach  3f  inch  before  its  form  was  recognizable.  Our  estimate 
of  the  length  of  lines  of  pressure  marked  out  by  laying  rods  upon 
the  skin  follows  the  same  principle. 

§  22.    Other   important   discoveries   as   to   the   skin's   so-called 


NATURE   OF   SENSATION-CIRCLES.  407 

"  sense  of  locality  "  have  been  made  since  those  of  Weber.  Valen- 
tin has  called  attention  to  the  fact  that  enormous  individual  differ- 
ences exist  in  the  fineness  of  this  kind  of  perception  ;  some  per- 
sons are  not  more  than  one-fourth  as  sensitive  as  are  some  others. 
The  relative  degree  of  fineness  belonging  to  different  areas  of  the 
skin  remains,  however,  approximately  the  same  in  different  persons. 
A.  W.  Volkmann  '  showed  the  remarkable  effect  of  exercise  upon  the 
cultivation  of  the  sense  of  localit}'.  After  fixing  the  value  of  the 
least  perceivable  differences  of  locality  for  a  number  of  small  areas 
in  the  field  of  touch,  Volkmann  found  that  each  successive  series  of 
experiments  with  each  area  increased  its  fineness  of  perception, 
until  within  a  few  hours  twice  the  original  degree  of  fineness  could 
be  reached.  The  growth  in  perceptive  skill  of  the  skin  was  slower 
at  first  for  areas  not  ordinarily  used  for  touch ;  quicker  for  those 
accustomed  to  daily  use.  The  improvement  ceased  at  a  certain 
limit,  and  was  soon  lost  by  disuse,  so  that  a  few  months  out  of 
practice  served  to  reduce  the  acquii-ed  tact  of  any  area  to  its  origi- 
nal condition.  A  most  surprising  discovery  of  this  experimenter 
was,  that  the  practice  exclusively  of  a  member  of  the  body  on  one 
side  resulted  in  improving  the  fineness  of  touch  of  the  correspond- 
ing member  of  the  other  side.  Thus,  if  the  smallest  perceivable 
distance  for  the  tip  of  a  left  finger  was,  to  begin  with,  0.75  line, 
and  that  of  the  corresponding  place  on  the  right  finger,  0.85,  prac- 
tice with  the  left  finger  exclusively  reduced  the  distance  for  both 
fingers — for  the  left  to  0.45  line,  and  for  the  right  to  0.4. 

It  is  well  known  that  the  blind,  who  have  no  spatial  series  of 
sensations  or  presentations  of  extended  objects  by  the  eye,  attain  by 
exercise  a  high  degree  of  fineness  for  certain  space-perceptions  of 
the  skin.^  In  the  case  of  those  who  have  sight,  the  most  movable 
and  discriminating  organs  of  the  skin — such  as  the  tips  of  the  fin- 
gers— are  capable  of  being  cultivated  to  great  delicacy  of  touch  ; 
but  Funke  ^  did  not  succeed,  even  by  an  education  lasting  an  en- 
tire month,  in  reducing  the  obtuseness  of  the  skin  of  the  back  be- 
tween the  shoulder-blades  and  in  the  lumbar  region  more  than  by 
about  one -fourth. 

§  23.  The  explanation  of  Weber's  "  sensation-cii'cles  "  of  the  skin 
has  been  the  subject  of  much  debate.  It  is  natural  at  first  to  as- 
sume that  each  entire  circle  is  provided  with  one  and  only  one 
nerve-fibre,  whose  terminal  expansion  covers  the  circle,  and  whose 
excitation  is  represented  in  consciousness  by  a  sensation  of  a  spe- 

'  Bericlite  d.  Sachsischen  Gesellschaft  d.  Wissenscliaften,  1858,  p.  38  f. 
^  Comp.  Czermak,  Sitzgsber.  d.  Wiener  Acad.,  XVII.,  Abth.  ii.,  p.  563  f. 
^  See  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  383. 


408  THE   FIELD    OF   TOUCH. 

cific  value.  Doubtless  certain  anatomical  differences  in  the  nerve- 
fibres  of  the  skin,  and  certain  corresponding  physiological  differ- 
ences in  their  function,  must  be  assumed  as  the  basis  of  every  the- 
ory to  account  for  the  skin's  sense  of  locality.  But  Goldscheider's 
experiments  show  that  a  number  of  pressure- spots  must  be  recog- 
nized within  each  sensation-circle,  and  each  pressure-spot  at  least 
should  have  a  sensory  fibre.  Moreover,  every  point  within  each 
sensation-circle  is  itself  sensitive  (however  large  the  circle  may  be), 
and  the  limits  of  none  of  the  circles  are  fixed  as  would  be  the  ex- 
panse of  a  single  nerve-fibre  distributed  over  them.  Still  further, 
different  individuals  differ  greatly  in  the  size  of  these  circles  (and 
we  cannot  well  suppose  a  corresponding  difference  in  the  number 
of  sensory  nerves  of  the  skin),  and  practice  suddenly  and  greatly 
diminishes  the  area  covered  by  a  single  circle.  It  must  at  least  be 
admitted  that  "  the  smallest  perceivable  distance  is  not  a  direct 
measure  for  the  diameter  of  the  sensation-circle."  ' 

Weber  himself  assumed  that  sensation-circles  always  contain  a 
number  of  isolated  nerve-fibres  ;  and  that,  in  order  to  have  the  im- 
pression of  two  localized  sensations,  several  unexcited  fibres  must 
exist  between  the  two  excited.  The  number  of  these  unexcited  fibres 
serves  the  mind  as  a  kind  of  means  for  the  approximate  measure- 
ment of  distances  on  the  skin.  Other  advocates  of  Weber's  ex- 
planation have  spoken  as  though  the  brain  could  somehow  become 
conscious  of  the  unexcited  fibres  lying  between  the  two  excited 
ones,  and  so  derive  a  support  for  its  judgment  from  their  num- 
ber.'' Of  course,  all  attempts  to  explanation  which  assume  the 
mind's  knowledge  of  the  condition  of  the  minute  subdivisions  of 
the  nervous  elements  are  wholly  futile  and  illusory.  Wundt  ^  cor- 
rectly calls  attention  to  the  fact  that  the  diflerences  in  the  so-called 
sensation-circles  of  the  skin  are  simply  a  special  case  under  the 
general  psychological  laws  of  the  least  observable  differences  in 
sensations  ;  oidy  in  this  case  the  differences  are  not  pure  differences 
in  intensity,  but  rather  differences  in  the  complex  color-tone  of  the 
quality  of  sensation.  In  other  words,  the  sensation-circles  represent 
the  local  difference  between  the  points  at  which  stimulus  must  be 
applied  to  the  skin  in  order  to  produce  enough  of  difference  in  the 
color-tone  of  the  resulting  sensations  to  make  them  observable  by 
the  mind.  These  local  signs  of  the  skin,  as  the  organ  of  touch 
proper,  like  all  local  signs,  are  complex  mixtures  of  feeling  belong- 
ing to  different  localities  ;  as  such  they  are  dependent,  not  only 

'  So  Funke,  in  Hermann's  Handb.  d.  Physiol.,  HI.,  ii.,  p.  392  f. 

'^  Comp.  Bernstein,  The  Five  Senses  of  Man,  p.  31  f.     New  York,  1876. 

^  Physiolog.  Psychologic,  ii  ,  p.  10. 


THE   THEORY    OF    VIEP^ORDT.  409 

upon  original,  anatomical,  and  physiological  differences,  but  also 
upon  other  peculiarities  of  the  individual,  upon  habit,  and  upon 
association  with  each  other  and  with  other  spatial  series  of  sensa- 
tions of  the  skin. 

§  24.  Difficulty  has  been  found  in  assigning  a  conclusive  reason 
why  the  different  areas  of  the  skin  should  differ  so  greatly  in  the 
fineness  of  their  capacity  for  making  local  distinctions.  In  the  view 
of  Lotze, '  this  difference  is  chiefly  due  to  the  varying  character  of 
the  areas  of  the  skin,  with  respect  to  richness  in  nerve-fibres,  thick- 
ness and  so  sensitiveness,  support  and  tension  according  as  the 
skin  is  stretched  over  underlying  soft  or  hard  parts — fat,  muscle, 
tendon,  bone,  etc.  Doubtless  all  such  influences  enter  into  the 
determination  of  that  mixture  of  feeling  which  characterizes  the  lo- 
cal signs  of  the  skin.  The  theory  suggested  by  Vierordt,^  on  the 
basis  of  experiments  made  by  himself  and  his  pupils,  should  also 
be  mentioned.  This  investigator  concluded  that  the  fineness  of 
the  sense  of  locality  belonging  to  any  area  of  the  skin  increases 
in  direct  proportion  with  the  distance  of  that  area  from  the  axes 
about  which  it  is  rotated.  The  relative  fineness  of  the  organ's  local 
sense  is  a  function  of  its  mobility.  Thus  an  uninterrupted  increase 
of  the  power  of  localization  exists  in  the  arm  from  the  acromion 
to  the  tips  of  the  fingers  ;  an  increase  of  its  movableness,  on  the 
whole,  also  exists.  If  a  value  of  100  be  assigned  to  the  power  of 
discrimination  exercised  at  the  acromion,  151  will  represent  that  of 
the  upper  arm,  272  that  of  the  lower  arm,  G59  of  the  hand,  2,417 
of  the  thumb,  and  2,582  of  the  tips  of  the  fingers.  In  estimating 
the  relative  movableness  of  these  different  parts,  it  should  be  re- 
membered that  they  not  only  all  move  in  an  enlarging  circuit  from 
the  shoulder- joint  downward,  but  that  each  of  them  from  the  el- 
bow-joint downward  has  its  special  increased  circuit  and  more 
numerous  forms  of  motion. 

But  even  if  Vierordt's  law  could  be  strictly  demonstrated  for 
every  portion  of  the  body,  its  meaning  would  have  to  be  translated 
into  other  terms  in  order  to  be  of  any  real  service  to  psychology. 
It  is  therefore  suggested  by  Funke  ^  that  the  increased  power  of 
discrimination  which  belongs  to  the  more  movable  areas  of  the 
skin  is  really  due  to  the  superior  facility  which  they  thus  have  for 
exercise  ;  it  therefore  falls  under  the  law  of  habit.  Furthermore 
— as  we  have  occasion  to  remark  concerning  many  similar  functions 

'  See  Medicin.  Psychologie,  p.  405  f. 

•2  Pflager's  Archiv,  1869,  ii.,  pp.  297  ff.  ;  aud  Zeitschr.  f.  Biologie,  VI.,  VII., 
IX  ,  X. .  XI. 

^  Hermann's  Handb.  d.  Physiol. ,  III  ,  ii  ,  p.  384. 


410  THE   FIELD    OF   TOUCH. 

of  tlie  mincT  in  correlation  with  the  nervous  mechanism — the  effect 
of  acquired  habit  is  not  Umited  to  the  experience  of  the  individual ; 
it  belongs  also  to  the  race.  The  superior  fineness  of  local  sense  in 
some  parts  of  the  body  may  therefore  be  regarded  as  largely  na- 
tive to  the  individual. 

§  25.  The  view  which  must  be  taken  of  Weber's  "  sensation-cir- 
cles," and  of  the  entire  subject  of  the  localization  of  areas  of  press- 
ure on  the  skin,  has  been  largely  changed  by  the  recent  experi- 
ments of  Goldscheider '  and  others.  We  have  already  seen  (p. 
346  f.)  that  this  experimenter  distinguishes,  more  carefully  than  has 
hitherto  been  done,  the  sensations  of  pressure  from  other  closely 
allied  sensations  coming  through  the  same  organ.  The  finest  point, 
when  it  touches  a  "pressure-spot,"  produces  a  sensation  of  pressure, 
and  not  one  of  being  pricked  ;  but  touching  other  spots  does  not 
produce  a  sensation  of  pressure  at  all.  It  must  be  held,  then,  that 
the  sensations  produced  by  laying  a  single  blunted  dividers'  point 
upon  the  skin,  as  in  Weber's  classical  experiment,  are  really  very 
complex,  and  are  composed  of  the  sensations  from  several  pressure- 
spots  blended  with  other  sensations  from  the  rest  of  the  same  area 
not  covered  by  the  pressure-spots.  The  fineness  of  discrimination 
possible  in  any  area  of  the  skin  depends,  then,  upon  how  all  the 
points  irritated  stand  related  to  the  specific  j)ressure-spots.  Gold- 
scheider  finds  that  only  when  two  irritating  points  touch  two  press- 
ure-spots are  thejfelt  as  two.  But  when  one  of  the  points  touches 
a  pressure-spot,  and  the  other  touches  some  place  in  the  contiguous 
area  of  skin  which  is  free  from  such  spots,  the  two  points  are  not 
both  felt ;  in  this  case  only  the  one  resting  on  the  pressure-spot  is 
felt. 

Moreover,  the  impression  of  being  doubly  touched  may  be  ex- 
cited by  the  points  when  lying  much  nearer  together,  in  case  they 
rest  upon  pressure-spots  that  belong  to  two  different  chains  of 
such  spots  than  when  both  spots  belong  to  the  same  chain.  This 
is  to  say,  pressure-spots  thus  located  have  a  high  degree  of  sensitive- 
ness. Still  further,  the  minimum  distance  required  to  produce  a 
sensation  of  being  touched  twice  is  surprisingly  small,  when  one  of 
the  touching  points  rests  upon  a  pressure-spot  from  which  the 
chain  radiates  or  at  which  it  makes  a  sharp  bend. 

The  table  of  minimum  distances  at  which  two  points  can  be  felt 
as  two,  when  the  exact  nature  of  the  area  of  the  skin  on  which  we 
are  experimenting  is  known,  and  everything  made  as  favorable  as 

'  On  this  STibject,  see  Goldscheider,  Arcliiv  f.  Anat.  u.  Physiol.,  Physiolog. 
Abth.,  1885,  Supplement-Band,  pp.  1-104;  especially,  p.  841 


DIEECTIOJSr   OF   THE   PRESSURE-SPOTS. 


411 


possible,  consists  of  numbers  very  much  reduced  from  those  of 
Weber.     Following  are  some  citations  from  Goldscheider's  table  : 


Part  of  the  bodj-.  mm. 

Back 4-6 

Breast 0.8 

Forehead 0.5-1.0 

Cheek 0.4-0.6 

Nose  and  chin 0.3 

Upper  and  lower  arm 0.5-1.0 


Part  of  the  body.  mm. 

Back  of  hand   0.3-0.6 

I.  and  II.  phalanges  (volar). .  0.2-0.4 
I.  and  II.  phalanges  (dorsal)..  0.4-0.8 

Upper  leg 3.0 

Lower  leg 0.8-2.0 

Backj  and  sole  of  foot 0.8-1.0 


From  the  foregoing  data  it  would  seem  to  follow  that,  as  the  con- 
struction and  relation  of  the  chains  of  pressure-spots  differ  in  the 
different  areas  of  the  body,  so  will  our  sense  of  locahty  change. 
The  number,  sensitiveness,  and  direction  in  the  chains  of  these 
spots  determine  the  sensitiveness  of  a  given  area.  Moreover,  our 
perception  of  the  size  and  shape  of  objects  in  contact  with  the  skin 
depends  upon  the  same  conditions.  This  can  be  shown  in  an  as- 
tonishing way  by  comparing  the  apparent  direction  which  the  out- 
lines of  any  small  body  moved  across  the  skin  seem  to  assume  with 
the  way  the  pressure-spots  are  located  in  the  different  areas  through 
which  it  is  moved.  If  the  curve  of  the  chain  of  pressure-spots,  for 
example,  bends  in  the  reverse  direction  from  that  of  the  outline  of 
the  body  moved,  the  eff'ect  may  be  to  make  this  outline  curve  ir- 
regularly or  even  straighten  it  out. 

It  need  scarcely  be  said  that  Goldscheider  regards  the  true  ex- 
planation of  these  phenomena  to  lie  in  the  anatomical  distribution  of 
the  specific  nerves  of  sense  in  the  different  areas  of  the  skin.  How- 
ever this  may  be,  it  is  certain  that  our  sensations  of  pressure  are 
primarily  "punctiform,"  and  afterward  massed  into  a  tactual  continu-, 
urn  ;  and  that  what  we  primaril}^  know  is  not  the  extended  object  aa 
such,  but  our  sensations  of  pressure  which  are  afterward  objectified. 

§  26.  Closely  connected  with  the  foregoing  is  the  difference  in 
power  of  different  parts  of  the  skin  in  giving  to  the  mind  data  for 
discriminating  the  fact,  the  amount,  and  the  direction  of  motion 
in  contact  with  the  body.  Upon  this  point  the  experiments  of  G. 
Stanley  Hall '  are  of  special  interest.  These  experiments  seem  to 
show  that  we  are  more  likel}',  when  in  doubt,  to  judge  motion  on 
the  surface  of  the  limbs  to  be  up  rather  than  down  their  axis  ;  on 
the  breast,  the  shoulder-blades,  and  the  back,  the  tendency  is  to 
judge  motion  to  be  toward  the  head.  The  discriminative  sensi- 
bility of  the  skin  for  motion  is  much  greater  than  that  for  sepa- 
rate touch,  as  determined  by  Weber's  experiments.     Thus,  while  at 


'  Motor    Sensations   on  the  Skin,  by   Professor  G.  S.  Hall   and  Dr.    H.  H 
Donaldson,  in  Mind,  October,  1885,  pp.  557  S. 


412  THE   FIELD   OF   TOUCH. 

least  a  distance  of  25  mm.  between  the  dividers'  points  was  needed 
on  the  volar  surface  of  the  right  arm,  in  oi'der  to  perceive  them 
as  two  points,  both  the  fact  and  the  direction  of  motion  could  be 
discriminated  at  an  average  distance  of  between  6  and  7  mm.  In 
judging  the  rate  and  distance  of  motion  over  the  skin  the  liabil- 
ity to  error  is  always  great ;  but,  as  a  rule,  distances  rapidly  trav- 
ersed are  judged  to  be  relatively  shorter  than  the  same  distances 
more  slowly  traversed.  Inasmuch,  however,  as  the  judgment  of 
motion  on  the  left  arm  was  expressed  by  reproducing  the  rate 
and  distance  with  the  right  hand,'  we  have  a  double  liability  to 
error  involved  in  regulating  the  muscular  movement  of  this  hand 
by  means  of  its  series  of  muscular  and  tactual  sensations. 

Hall  found  the  motor  sensibility  of  different  parts  of  the  surface 
of  the  skin  to  be  different ;  but  the  differences  do  not  appear  to 
correspond  to  those  belonging  to  Weber's  sensation -circles.  The 
average  distance,  in  millimeters,  which  a  metallic  point  of  12  mm. 
in  diameter  could  move  over  the  skin  at  a  rate  of  2  mm.  per  second 
before  a  judgment  of  direction  could  be  formed  was  found,  for  one 
subject  of  experiment,  as  follows:  forehead,  0.20;  upper  arm,  0.40; 
forearm,  0.44;  shin,  0.60;  ]Dalm,  0.74;  back,  0.85.  Motion  can  be 
produced  so  slowly  as  not  to  be  discriminated  at  all,  even  when  the 
body  in  contact  has  really  moved  from  6  to  12  centimeters.  It  can 
also  be  produced  so  rapidly  as  to  make  it  impossible  to  tell  when  it 
begins  and  when  ends.  Heavy  weights  seem  to  move  faster  than 
light  ones  going  at  the  same  rate  ;  but  here  other  sensations  are 
called  out  by  the  deep  pressure,  and  combined  with  those  of  con- 
tact. Hall  concludes  that  heat-spots  and  cold-spots  traversed  by 
the  moving  body  are  of  great  service  in  judging  motion  and  its  di- 
rection on  the  skin  ;  the  cold-spots  more  than  the  heat  spots,  "be- 
cause of  the  fainter  sensation  and  wider  irradiation  "  of  the  latter. 

Further  experiments  with  a  travelling  metallic  point  that  carried 
the  stimulus  of  an  electrical  current  over  the  surface  of  the  skin 
showed  an  astonishing  diversity  of  sensations  developed  at  different 
points  of  the  area  thus  traversed.  Points  of  cutting  pain,  "  thrill- 
points,"  "  tickle-points,"  "  acceleration-points  "  (or  places  where  the 
rate  of  motion  seems  suddenly  to  increase  without  any  real  change 
in  the  speed  of  the  moving  metal),  "  blind-points  "  (or  spots  where 
all  impression  of  contact  is  momentarily  lost),  are  all  to  be  differen- 
tiated. Yet  the  sharp  differentiation  of  these  sensations  is  ren- 
dered difficult  by  the  fact  that  the  various  kinds  are  so  impacted 
and  run  together,  in  a  tangle  of  sensation.  The  experimenters  also 
speak  as  though  many  dermal  sensations  may  thus  be  partially  dis- 
'  Miud,  October,  1885,  p.  564  f. 


nxEXESS  OF  te:.ipe::atui^3-3ense. 


413 


entangled,  for  the  description  of  whicli  language  furnishes  no  ade- 
quate terms.  All  these  facts  agree  exceedingly  well  with  the  theory 
of  local  signs  already  proposed.  These  dermal  signs  are  complex 
"mixtures"  of  feeling,  which  give  to  each  discernible  locahty  a 
characteristic  local  stamp.  The  fact  that  our  sensibility  to  motion 
is  so  much  greater  in  each  area  of  the  skin  than  our  susceptibility 
to  the  distance  of  stationary  points  accords  with  the  same  theory. 
Our  ability  to  localize  the  dermal  sensations  is  dependent  upon  the 
degree  and  I'ate  of  the  changes  in  the  color-tone  of  these  sensations. 
Hall  is  undoubtedly  right  in  holding  that,  by  moving  the  touching 
surface  over  the  surface  touched,  we  do  not  simply  multiply,  but 
also  diversify,  our  data  for  filling  up  the  dermal  blind-spots  and 
judging  the  nature  of  impressions. 

§  27.  The  localizing  of  sensations  of  temperature  in  the  skin  is, 
in  principle,  the  same  as  that  of  sensations  of  light-pressure  or  of 
motion.  The  former,  however,  are  in  all  our  ordinary  experience 
interwoven  with  the  latter  ;  they  therefore  have  the  help  of  the  lat- 
ter in  getting  a  place  assigned  to  them  in  the  periphery  of  the 
body.  Recent  researches,  akeady  referred  to  (Chap.  IV.,  §  22),  dem- 
onstrate the  fact,  that  the  relative  number  and  arrangement  of 
heat-spots  and  cold-spots  is  different  for  different  areas  of  the  skin. 
Goldscheider  '  has  ex]3erimented  to  determine  how  far  apart  the 
heat-spots  and  cold-spots  must  be,  respectively,  in  oixler  that  two 
of  them,  when  stimulated,  may  he  felt  as  two.  Both  kinds  of  sen- 
sations ai'e  localized,  not  as  points,  but  as  minute  warm  or  cold 
drops  in  contact  Avith  the  skin.  By  the  following  table,  which 
gives  the  minimum  distances  for  different  areas  of  the  body,  it  ap- 
pears that  the  sense  of  locality  connected  with  the  cold-spots  is 
about  twice  as  fine,  as  a  rule,  as  that  connected  with  the  heat-spots. 
The  distances  are  given  in  millimeters. 


Part  of  the  body. 

Cold-spots. 

Heat-spots. 

Forehead,  cheek,  and  chin   

0.8 

3.0 

1-3 
1.5-3.0 
1.5-3.0 

3-3 

0.8 

3-3 

3-5 

Breast   

4^5 

Abdomen 

4-6 

Back     

4-6 

Upper  arm   

3-3 

Lower  arm    ...      . 

3-3 

Hollovv  of  the  hand     - 

3.0 

Back  of  the  hand,  and  upper  and 

lower  \e 

s. . .  . 

3^ 

'  Archiv  f .  Auat.  u.  Physiol. ,  Physiolog. 
70flE. 

Abth. 

1885, 

Supplemen 

t-Band,  pp. 

414  THE   FIELD   OF  TOUCH. 

Some  basis  seems  to  be  laid  in  the  foregoing  facts  for  a  system 
of  local  signs  of  the  skin,  that  consist  in  a  mixture  of  color-tones  of 
temj)erature-sensations.  Yet  sensations  of  heat  or  cold,  in  them- 
selves considered,  differ  chiefly,  if  not  wholly,  in  intensity.  In  them- 
selves, therefore,  they  are  not  vs^ell  fitted  to  constitute  a  so-called 
"  spatial  series  "  of  sensations.  If,  for  example,  a  certain  area  of 
the  skin  be  stimulated  simultaneously  by  both  heat  and  cold,  at 
points  too  near  together  to  be  distinguished  by  touch,  the  result  is 
neither  a  modification  of  one  sensation  by  the  other  nor  a  localizing 
of  the  two  sensations  as  lying  closely  side  by  side,'  A  wavering  of 
perception  rather  takes  place,  similar  to  the  strife  of  coloi'S  in  vi- 
sion ;  the  experience  is  as  though  the  skin  were  being  touched  with 
a  single  body  alternately  hot  and  cold.  Klug  also  found  that  the 
least  observable  distance  between  two  points  touching  the  skin  at 
the  same  time  depends  upon  their  temperature  relative  to  that  of 
the  skin.  The  medium  value  of  this  distance  is  reached  when  these 
points  have  a  temperature  of  20°-40°  C.  (68°-104°  Fahr.) ;  it  dimin- 
ishes on  either  raising  or  depressing  their  temperature  greatly 
above  or  below  the  zero-point  of  the  skin.  The  fineness  of  our 
sense  of  locality,  as  well  as  of  our  sensitiveness  to  motion  (comp. 
§  25),  is  increased  by  exciting  sensations  of  temperature  up  to  the 
point  where  pain  intervenes.  But  the  localizing  of  these  sensations 
is  primarily  dependent,  to  a  great  extent,  upon  their  connection 
with  localized  sensations  of  touch.  If  we  bring  two  parts  of  the 
skin,  that  differ  considerably  in  temperature,  into  contact — for  ex- 
ample, a  cool  hand  and  warm  forehead,  or  a  cool  hand  and  a  warm 
one — it  is  often  difficult  by  strict  attention  to  the  sensations  of  tem- 
perature alone  to  tell  which  part  is  cooler,  which  warmer.  The 
difficulty  is  doubtless  largely  due  to  the  fact  that  each  part  which 
feels  the  temperature  of  the  other  is  also  changing  its  own  tem- 
perature in  the  direction  of  the  temperature  of  the  other.  It  is 
therefore  induced  to  feel  itself,  as  it  were,  as  being  of  the  tempera- 
ture of  that  other.  A  confusion  of  the  data  for  judgment,  accord- 
ingly, takes  place.  Any  localization  of  the  sensations  which  occurs 
under  such  circumstances  is  largely  dej^endent  upon  secondary  con- 
siderations, and  especially  upon  the  direction  of  tbe  attention. 

We  judge  of  depth  by  sensations  of  temperature,  indirectly,  and 
through  our  ability  to  remove  or  change  the  intensity  and  locality 
of  these  sensations  by  changing  the  position  of  the  body  in  space 
as  related  to  what  we  know  to  be  hot  and  cold  bodies  or  surround- 
ing media. 

'  See  Czermak,  Sitzgsber.  d.  Wiener  Acad. ,  March,  1855,  p.  500;  confirmed 
by  Klug  and  others. 


'    nSTATUEE   OF   THE   MUSCULAE   SEISTSE.  415 

§  28.  The  specific  sensations  of  the  viuscular  sense  constitute 
another  spatial  series  which  combines  with  the  foregoing  in  the 
localizing  of  areas  at  the  periphery,  and  of  external  objects  as 
projected  in  space  and  yet  known  as  in  contact  with  the  body.  In- , 
deed,  it  is  upon  this  particular  system  of  local  signs  that  the  mind 
is  chiefly  dependent  for  its  data — other  than  the  visual — in  the 
synthetic  construction  of  its  presentations  of  bodies  that  stand  re- 
lated to  each  other  in  three  dimensions  in  objective  space.  Three 
principal  theories  have  been  held  as  to  the  nature  of  the  so-called 
muscular  sensations :  (1)  So  far  as  they  are  not  tactual,  they  are  to 
be  resolved  into  "  central  feelings  of  innervation,"  which  differ  only 
in  intensity  and  not  in  specific  quality,  and  which  result  from  the 
changes,  initiating  movement  of  the  bodily  organs,  that  take  place 
in  the  brain  as  correlated  with  impulses  of  the  will  (so  Wundt,  and 
others)  ;  (2)  they  are  not  specific  sensations,  but  are  due  to  interj)re- 
tations  of  those  feelings  in  the  skin  which  originate  on  account  of 
its  changes  of  position,  tension,  etc.,  as  the  underlying  muscles  are 
moved  (so  Schiff,  and  others) ;  (3)  they  are  specific  sensations  de- 
pendent on  a  specific  nerve-apparatus  of  sense,  which  has  its  end- 
organs  in  the  muscle-fibre,  and  which  is  excited  by  the  contraction 
of  the  latter  in  a  manner  dependent  upon  the  kind,  amount,  and 
direction  of  the  muscular  movement  taking  place  (so  Bell,  Weber, 
Funke,  and  others). 

We  have  already  given  certain  reasons  for  rejecting  the  first 
two  and  accepting  the  last  of  the  foregoing  views  (see  p.  344  f.) ; 
other  reasons  will  be  mentioned  subsequently  in  discussing  the 
so-called  "feeling  of  innervation"  or  of  "active  energy."  The 
muscular  sense,  like  all  the  other  senses  which  contribute  to  our 
presentations  of  objects  extended  in  space,  appears  to  have  its  own 
system  of  local  signs.  The  muscular  sensations  are  qualitatively 
(and  not  merely  quantitatively)  different,  according  to  the  combi- 
nation of  the  muscles  moved,  and  according  to  the  extension  over 
the  muscular  area  of  the  stimulus  imparted  to  the  sensory  nerve- 
fibres  situated  in  the  muscle  by  the  changing  condition  of  the 
latter  as  it  contracts  and  relaxes.  The  series  of  sensations— with 
all  the  qualities  of  rapid  and  nice  gradations  which  belong  to 
"spatial  series"  of  sensations — called  out  by  moving  one  limb  dif- 
fers from  that  called  out  by  moving  another  limb.  At  each  step  in 
the  flexing  of  the  leg — for  example — the  color- tone  of  the  muscular 
sensations  has  a  specific  quality  and  value  as  a  local  sign,  in  our 
consciousness,  of  the  position  of  the  member.  The  same  thing  is 
true  of  the  bending  arm,  back,  or  single  toe  or  finger.  These  sen- 
sations are  intimately,  and  even  inextricably,  combined  with  the 


416  THE    FIELD    OF   TOUCH. 

spatial  series  of  specifically  dermal  sensations  ;  but  in  tliemselvea 
they  have  a  different  quality,  and  are  not  localized  simply  at  the 
surface  of  the  body.  As  the  extent  of  the  circuit  of  motion  gone 
through  by  any  limb  increases,  or  the  intensity  of  the  strain  be- 
comes greater,  the  quality  of  the  mass  of  resulting  muscular  sensa- 
tions is  perpetually  changing.  These  sensations  are,  accordingly, 
localized  over  a  broader  area  of  the  body  and  deeper  in  its  sub- 
stance, as  it  were.  Everyone  knows  Avhat  new  mixtures  of  sensa- 
tion are  produced  in  consciousness  by  calling  into  vigorous  exer- 
cise the  unused  more  deeply  lying  muscles  of  the  body.  Bain'  has 
discussed  these  sensations  at  great  length  and  with  commenda- 
ble acuteness.  But  the  apparent  assumption  that  these  particu- 
lar sensations  can,  by  being  associated,  acquire  of  themselves  the 
quality  of  extension  in  space,  and  the  accounting  for  all  our  other 
perceptions  of  spatial  qualities  and  relations  as  merely  secondary 
and  symbolic  of  the  associated  muscular  sensations,  are  in  plain 
contradiction  of  established  psychological  facts  and  principles. 

The  muscular  sensations  also  assist  the  more  strictly  tactual  in 
discriminating  locality  for  all  cases  where  the  pressure  upon  the 
skin  exceeds  a  certain  small  degree  of  intensity.  In  strong  contact 
or  heavy  pressure  the  sensory  nerves  of  the  underlying  muscle  are 
excited ;  we  have  the  feeling,  not  simply  of  being  touched,  but  also 
of  being  pressed.  The  combination  of  these  two  spatial  series 
gives  to  the  mind  a  doubly  constituted  system  of  local  signs ;  hence, 
as  the  experiments  of  G.  Stanley  Hall  ^  show,  our  judgment  of  di- 
rection of  motion  is  quicker  as  the  weight  resting  on  the  skin  is 
increased  up  to  the  limit  where  other  disturbing  sensations  inter- 
vene. The  sui^erior  discriminating  power  which  any  member  of 
the  body  has  when  permitted  to  move — that  is,  to  call  forth  fa- 
miliar series  of  muscular  sensations — is  largely  due  to  the  help 
which  the  local  signs  of  this  system  render  to  the  mind.  When 
the  particular  member  (the  hand)  which  is  capable  of  the  nicest 
tactual  discrimination  is  also  permitted  to  move  over  an  object 
freely,  and  to  acquire  abundant  data  from  all  the  sources  described 
above,  we  have  fulfilled  the  most  advantageous  conditions  for  the 
utmost  nicety  of  knowledge  possible  to  "  touch,"  in  the  Avidest 
meaning  of  the  word. 

§  29.  It  is  unnecessary  to  illustrate  in  further  detail  the  process 
by  which  the  mind,  with  its  native  synthetic  activity,  and  with 
the  help  of  qualitatively  different  sensations,  constructs  its  field  of 

'  The  Senses  and  the  Intellect,  especially  pp.  57-100,  336-348,  and  364- 
398. 

2  Mind,  October,  1885,  p.  567. 


RELATIOIS^S    OF   EYE   AND   HAND.  417 

touch.  To  multiply  instances  would  neither  explain  the  ultimate 
mystery  which  enters  into  the  processes  of  "  localization  "  and  "  ec- 
centric projection "  by  touch,  nor  add  materially  to  our  compre- 
hension of  known  psycho-physical  principles.  The  muscular  sense 
may  pi'obably  be  said  to  have  the  leading  position  in  the  develop- 
ment of  the  perception  of  spatial  objects  and  relations,  so  far  as 
attainable  without  the  aid  of  sight.  Perceptions  of  the  magnitude, 
distance,  and  primary  spatial  qualities — such  as  the  extension  and 
inertia — of  material  things  are  largely  dependent  upon  associated 
sensations  of  the  muscular  sense,  although  these  perceptions  cannot 
be  said  to  be  mere  compounds  of  such  sensations  with  secondary 
and  symbolic  sensations  of  other  kinds  added  to  them.  The  activ- 
ity of  the  hand,  as  it  moves  over  various  surfaces  of  the  body,  either 
touching  them  itself  or  carrying  with  it  something  with  which  these 
surfaces  are  touched,  early  combines  with  the  different  series  of 
muscular  sensations  other  spatial  series  of  tactual  sensations. 

The  localization  of  certain  points  in  the  area  of  the  body  which 
are  of  marked  local  characteristics,  and  frequently  recurrent  in  ex- 
jDerience,  is  the  first  achievement  in  constructing  the  field  of  touch. 
To  these  landmarks,  as  it  were,  other  points  or  areas,  subsequently 
discovered,  are  referred.  One  hand  learns  to  know  the  other  ;  the 
right  hand  chiefly  exjDlores  the  left  arm  and  side  and  the  upper  right 
leg  ;  the  left  hand,  the  right  arm  and  side  and  the  upper  left  leg*. 
The  finger-tips,  especially  of  the  right  hand,  have  an  office  similar 
to  that  performed  by  the  yellow-spot  of  the  retina ;  they  are  the 
centre  or  hearth  of  clear  perceptions  of  touch.  But  in  order  to 
bring  them  to  their  object  they  must  be  moved ;  through  this  mo- 
tion fresh  combinations  of  muscular  and  tactual  sensations  result. 

§  30.  But  long  before  the  entire  field  of  touch  has  been  con- 
structed with  any  considerable  appi'oach  to  comj)leteness,  the  eye 
has  already  explored  those  parts  of  the  body  which  are  open  to  its 
inspection.  It  learns  first  to  know  the  hand,  which  nature  keeps 
constantly  in  motion  before  it.  As  objects  rest  on  the  hand,  it 
notes  the  place  where  they  rest ;  with  its  perceptions  of  sight  cer- 
tain combinations  of  tactual  sensations  thus  become  associated.  As 
the  hand  moves  over  other  objects,  or  especially  over  the  other  parts 
of  the  body,  the  eye  marks  its  successive  progress  ;  combined  sen- 
sations of  muscular  and  tactual  kind  are  thus  associated  with  each 
position  of  the  hand  and  with  each  area  of  the  body  which  it  touches. 
Very  early  in  the  development  of  a  normal  experience  the  eye  comes 
to  be  the  leader  and  critic  of  the  discriminations  connected  with 
the  muscular  and  tactual  sensations.  Its  power  of  rapid  movement 
over  its  total  field,  and  its  delicate  judgment  on  account  of  the 
27 


418  THE   FIELD    OF   TOUCH. 

finely  sliadecT  complex  local  signs  which  it  calls  forth  with  a  com- 
prehensive simultaneousness,  give  a  great  superiority  to  the  organ 
of  vision  as  a  geometrical  sense.  The  results  of  such  superiority  it 
constantly  places  at  the  disposal  of  the  more  slowly  moving  and 
less  delicate  sense  of  touch.  For  this  reason,  one  born  blind  can 
never  attain  the  same  quality  (of  "  comprehensive  simultaneous- 
ness ")  for  his  sj)atial  intuitions  and  ideas  of  spatial  relations  ;  even 
the  field  of  touch,  in  spite  of  the  greater  refinement  which  the 
muscular  and  tactual  sensations  of  such  an  unfortunate  person  ac- 
quire through  use,  cannot  possess  this  quality  as  it  is  imparted  by 
the  eye. 

The  familiar  experiments  of  trying  to  estimate  the  size,  shape, 
and  relation  of  objects,  the  amount  and  direction  of  motion,  etc., 
when  blindfold,  show  our  dependence  upon  the  organ  of  sight.  It 
must  not  be  forgotten,  however,  that  the  discriminations  possible 
through  the  muscular  and  tactual  sensations  alone  are  wonderfully 
exact ;  and  that  in  certain  circumstances  touch  has  sight  at  a  dis- 
advantage, as  it  were.  Thus  the  player  on  the  violin  who  should 
adjust  his  spacing  of  the  strings  by  the  sensations  of  the  eye,  with 
the  unaccustomed  and  unfavorable  perspective  made  necessary  by 
its  position  in  relation  to  the  left  hand,  would  not  attain  the  art  of 
making  true  and  pure  tones. 

§  31.  Among  the  most  complex  perceptions  of  which  the  skin 
and  muscles  by  their  combined  action  are  capable  are  the  so-called 
"feelings  of  double  contact."  It  is  largely  by  means  of  these  feel- 
ings that  skill  is  acquired  in  the  use  of  tools,  weapons,  and  musi- 
cal instruments.  In  these  cases  the  process  of  projection  goes  so 
far  that  we  seem  to  feel  the  object  with  which  the  implement  is  in 
contact,  not  so  much  in  the  hand  (the  feelings  of  contact  being 
located  there),  by  the  external  means  of  the  implement,  but  rather 
as  ourselves  being  in  the  implement  and  using  it  as  a  sentient  part 
of  the  organism.  The  carver  in  wood  feels  his  chisel  move  through 
the  stuff  he  is  shaping,  and  guides  it  as  unerringly  as  he  would  his 
finger,  so  as  to  lay  it  with  a  given  degree  of  pressure  upon  a  given 
spot.  We  are  all  familiar  with  the  experience  of  feeling  the  ground 
we  are  about  to  tread,  with  a  cane  or  other  stick.  If  the  fingers  be 
lightly  brushed  over  the  hair  when  it  stands  out  from  the  head,  it 
will  be  difficult  to  localize  the  sensations  of  pressure  at  the  scalp 
rather  than  in  the  hair.  We  feel  the  touch  of  our  finger  at  the  end 
of  the  tooth,  where  the  contact  takes  place,  instead  of  where  the 
sensory  nerves  really  receive  the  stimulus  and  convert  it  into  a 
nerve-commotion 

The  management  of  the  implement  is,  of  course,  really  made 


FEELINGS   OF  DOUBLE   CONTACT.  419 

possible  by  delicate  changes  in  the  shades  of  feeling  called  out  by 
its  changing  pressure  upon  the  nerves  terminating  in  the  skin  and 
muscles  of  the  hand,  and  by  the  accompanying  feelings  of  strain 
and  of  effort  that  result  from  the  movement  of  the  arm  which 
carries  the  hand.  These  feelings  are  aroused  by  the  end  of  the 
implement  which  is  in  contact  with  the  body,  and  are  primarily 
localized  in  that  pai't  of  the  body ;  but  they  are  felt  through  a 
more  artificial  and  elaborate  process  of  localization,  as  though  di- 
rectly dependent  upon  the  other  end  of  the  implement.  Upon  the 
aesthetic  and  pleasurable  uses  of  these  feelings  of  double  contact 
Lotze  '  has  remarked  at  length. 

At  this  point  the  further  discussion  of  the  development  of  our 
presentations  of  sense  in  general  must  be  arrested,  in  order  to  con- 
sider more  in  detail  the  activities  of  the  other  great  "  geometrical 
sense." 

'  See  Microcosmus,  i.,  pp.  586  ff.     Edinburgh,  1885. 


CHAPTEE  YII. 
THE  PEESENTATIONS  OF  SENSE.    [Continued.] 

§  1.  The  application  of  the  general  princij)les  which  control  the 
development  of  our  presentations  of  sense  to  the  particular  case 
of  the  eye  has  many  peculiar  difficulties.  The  physiological  psy- 
chology of  visual  perception  is,  therefore,  a  much  controverted  and 
very  obscure  domain.  This  fact  is  doubtless  in  part  due  to  the 
amount  of  experimenting  and  speculating  which  has  been  be- 
stowed upon  it.  For  here,  as  elsewhere  in  scientific  research,  one 
chief  result  of  extended  examination  is  to  raise  unanswered  in- 
quiries. Peculiar  difficulties,  however,  are  intrinsic  in  the  case  of 
the  eye.  These  are  due  to  the  great  complexity  of  its  native 
activities,  and  to  the  speed  with  which  it  reaches  a  generous 
maturity  of  development.  Nature  has  equipped  this  organ  with 
superior  means  for  furnishing  to  the  mind  a  variety  of  data,  as 
respects  both  quantity  and  quality,  for  the  nicest  discriminations  ; 
it  has  also  provided  it  with  such  constant  stimulation  as  to  cause 
it  to  acquire  an  incomparable  facility.  But  the  character  of  its 
structure,  functions,  and  development  is  such  as  to  make  experi- 
ment difficult  in  a  way  to  disentangle  the  simple  factors  from  those 
complex  forms  into  which  the  synthetic  activity  of  the  miud  has 
constructed  them. 

§  2.  It  is  affirmed  by  one  authority  '  that  no  less  than  eight 
different  data,  or  motifs,  are  used  in  monocular  vision  by  the 
adult  for  perceiving  the  third  dimension  of  space  and  of  visual 
objects  in  space.  These  are  the  changes  with  respect  to  (1)  extent 
and  (2)  clearness,  of  the  complex  of  the  sensations  of  color  and 
light,  as  dependent  on  distance  ;  (3)  the  perspective  elevation  of 
the  bottom  of  distant  objects  above  the  horizon ;  (4)  the  covering 
of  known  distant  objects  by  those  placed  nearer  ;  (5)  the  alter- 
ations of  light  and  shadow  on  the  curved  surfaces  of  the  object, 
according  as  they  are  nearer  or  more  remote  ;  (6)  the  perspective 
contraction  of  the  retinal  image  ;  (7)  the  change  of  the  visor  angle 
in  proportion  to  the  distance  of  the  object ;  (8)  the  muscular  sen- 
'  Volkmann  vou  Volkmar,  Lehrb.  d.  Psychologies  II.,  p.  84. 


PKOBLEM   OF   VISUAL   PERCEPTION-.  421 

sations  of  the  accommodation  of  the  eye.  To  these  eight  data,  two 
others  at  least  must  be  added  for  binocular  vision  ;  namely  (9),  the 
stereoscopic  double  images,  and  (10)  the  sensations  arising  from 
convergence  of  the  axes.  These  ten  sets  of  variable  experiences  may 
be  combined,  of  course,  in  an  almost  infinite  variety  of  proportions. 

Moreover,  it  is  not  improbable  that  we  shall  have  to  admit  still 
other  data  as  entering  into  the  complex  perceptions  of  sight.  The 
tactual,  as  well  as  muscular,  sensations  which  accompany  the  move- 
ment of  the  eyeballs  in  their  sockets  are  not  ineffective  in  giving 
grounds  for  judgment  in  certain  cases.  The  question  must  also 
be  raised  :  Do  not  the  visual  sensations  themselves  have  a  certain 
local  coloring  directly  dependent  upon  the  nervous  elements  of 
the  retina  which  are  excited  by  the  stimuli  ?  If  we  answer  this 
question  affirmatively,  we  shall  have  a  system  of  local  retinal  signs 
as  constituting  one  of  the  most  primary  of  the  spatial  series  of 
sensations  entering  into  the  space-perceptions  of  this  sense.  And 
after  all  this  cataloguing  of  data,  the  dispute  as  to  the  existence  of 
series  of  sensations  of  innervation  that  have  a  central  origin  and 
differ  only  in  intensity  as  directly  dependent  upon  so-called  acts  of 
will  (so  Wundt)  remains  unsettled. 

Several  of  the  data  just  enumerated,  however,  are  plainly  of  only 
secondary  rank  and  value  ;  they  do  not  necessarily  enter  into  every 
preception  of  a  visual  object  as  such.  What  does  seem  necessary 
to  the  most  elementary  form  of  visual  perception  may  be  stated  as 
follows  :  Sensations  of  light  and  color,  differing  in  intensity  and  qual- 
ity, hut  simultaneously  present  in  consciousness,  must  be  systematically 
arranged  with  reference  to  each  other  by  being  localized  with  the  help 
of  retinal  signs,  and  associated  with  other  spatial  series  of  muscular 
sensations  that  arise  from  accommodation  of  the  eye  and  from  its 
motion.  The  complexity  of  the  combinations  arising  in  the  normal 
use  of  the  organ  of  vision  is,  of  course,  increased  by  the  fact  that 
there  are  two  eyes,  and,  therefore,  two  retinas  with  their  systems 
of  retinal  signs,  two  images  of  each  object,  and  two  sets  of  motions. 
But  the  two  eyes  are  (as  we  shall  see  subsequently)  in  a  certain 
sense  to  be  regarded  as  one  eye — certainly  as  constituting  one 
organ  of  vision.  So  that,  even  when  one  eye  is  closed,  the  other 
does  not  see  what  it  sees  without  being  influenced  by  the  closed 
and  relatively  inoperative  part  of  the  one  organ.  The  constancy 
with  which  the  eyes  act  together  explains,  in  part,  why  they  are  one 
organ  as  the  two  hands  are  not  ;  but  the  frequency  with  which  avb 
voluntarily  suppress  the  activity  of  one  eye  by  closing  it  explains, 
in  part,  why  they  are  not  one  organ  as  are  the  two  nostrils  or  the 
two  ears. 


422  DATA   OR  MOTI"FS   OF   VISION. 

§  3.  Could  we  select  an  adult  human  being  who  had  never  seen, 
and  proceed  to  develop  his  visual  perceptions,  experimentally,  in 
the  direct  order  of  their  complexity,  we  might  possibly  rely  upon 
his  description  of  his  experience  to  solve  certain  problems  that  now 
seem  unsolvable.  We  should  wish,  before  either  eye  had  been 
moved  when  open,  to  excite  the  nervous  elements  of  a  small  area  of 
one  stationary  retina,  and  to  ascertain  how  far  the  sensations  of  light 
and  color  thus  excited  could  be  said  to  have  any  strictly  "local" 
ari'angement  with  reference  to  each  other.  We  should  then  wish 
to  try  the  effect  of  combining  with  these  sensations  other  spatial 
series,  consisting  of  muscular  sensations  and  arising  from  the  ac- 
commodation and  motion  in  its  orbit  of  the  same  eye.  Finally,  the 
intricate  process  of  putting  the  two  eyes  together — both  open  and 
both  moving — might  be  studied  in  detail.  At  present,  however, 
it  is  quite  impossible  to  say  what  the  experience  of  the  subject  of 
such  experiments  would  be.  The  testimony  of  the  few  blind  per- 
sons whose  eyes  have  been  couched  is  so  meagre  and  unsatisfac- 
tory, on  account  of  its  failure  to  comply  with  the  conditions  of 
scientific  investigation,  that  it  can  be  used  only  to  confirm  con- 
clusions arrived  at  on  other  grounds.  Nothing  remains,  then,  but 
to  employ  the  data  which  physiological  optics  has  secured,  in  order 
to  make  a  theoi'etic  reconstruction  (confessedly  imperfect  and  doubt- 
ful) of  the  process  that  nature  is  all  the  while  successfully  com- 
pleting. In  this  effort  we  naturally  follow  the  order  of  nature,  so 
far  as  possible  ;  we  begin  with  the  simplest  conceivable  case,  and 
proceed  f  I'om  it  to  the  explanation  of  the  amazing  complexity  which 
really  belongs  to  our  apparently  simple  daily  experience  of  vision 
with  two  trained  eyes.  This  is  substantially  the  course  followed 
by  Wundt,'  who  finds  three  things  to  be  considered  in  explaining 
the  develoj)ed  perceptions  of  sight :  (1)  The  retinal  image  of  the 
eye  at  rest,  and  the  motifs  which  it  furnishes  ;  (2)  the  single  eye 
as  moved,  and  the  influence  of  these  movements  ;  (3)  the  conditions 
furnished  by  the  existence  and  relations  of  the  two  eyes  exercis- 
ing their  functions  in  common.  But,  in  reality,  from  the  very  be- 
ginning of  its  activity  the  eye  is  in  motion,  and  acts  as  a  double 
organ. 

Corresponding  to  the  three  sets  of  considerations  just  mentioned, 
we  may  speak  of  three  fields  of  vision  which  are  to  be  constructed 
in  the  order  of  their  complexity.  They  may  be  called,  resi^ectively, 
the  retinal  field  of  vision,  the  field  of  monocular  vision,  and  the 
field  of  binocular  vision.  In  the  "retinal  field  of  vision  "  we  mean 
to  include  only  such  a  percejotion — or  mental  spatial  arrangement 
'  Pliysiolog.  Psychologie,  ii. ,  p.  63. 


NATURE    OF   THE   EETIISTAL   FIELD.  423 

of  sensations  of  color  and  light  as  points  lying  side  by  side — as 
would  be  presented  through  the  excited  expanse  of  nervous  ele- 
ments constituting  the  retina  of  one  motionless  eye,  in  case  there 
had  been  no  previous  vision  with  both  eyes  in  motion.  The  field 
of  monocular  vision,  when  completely  constructed,  includes  all  that 
can  be  seen  with  one  eye  as  the  result  of  its  experience,  devel- 
oped, but  unaided  by  the  other  eye.  The  field  of  binocular  vision 
includes  all  that  can  be  seen  by  both  eyes.  The  first  two  so- 
called  "  fields  of  vision  "  are,  strictly  speaking,  fictitious  and  theo- 
retically constructed  in  order  to  explain  the  process  by  which  the 
mind  reaches  the  construction  of  the  third  and  last.  Indeed,  the 
question  may  be  pressed,  whether  we  can  speak  of  a  purely  "  retinal 
field  of  vision,"  and  whether  the  excited  mosaic  of  nervous  elements 
on  which  the  image  is  formed,  without  aid  from  muscular  sensations 
of  the  eje,  could  furnish  any  presentations  of  sight. 

§  4  The  most  nearly  original  experience  of  sensations  of  light 
and  color  which  can  be  easily  produced  for  adult  observation  is 
gained  by  closing  and  blindfolding  both  eyes,  and  then  keeping 
them  as  motionless  as  possible.  Let  time  enough  be  allowed  for 
all  the  after-images,  both  positive  and  negative,  to  die  wholly  away. 
Nothing  is  then  seen  but  a  small  and  undefined  expanse  or  massive 
aggregate  of  related  color-sensations,  which  we  will  call  the  "  ret- 
inal field  ; "  it  might  almost  be  said  that  this  is  felt  rather  than 
seen.  Such  "  vision  "  (?)  of  a  certain  continuum  of  sensations  can- 
not be  said  to  be  either  localized  or  j^rojected  in  space,  as  a  whole, 
and  by  the  eye  alone.  When  we  speak  of  it,  for  example,  as  "  in 
front  of  "  the  upper  part  of  the  body,  we  introduce  terms  that  are 
derived  from  experiences  of  touch.  Now,  without  moving  or  un- 
covering the  eyes,  let  the  head  be  turned  to  the  right  or  to  the 
left,  and  the  expanse  of  color-sensations  will  move  in  the  same 
direction  ;  or,  if  we  turn  the  face  upward,  the  retinal  field  seems 
above  us  ;  if  downward,  then  it  seems  to  sink  toward  our  feet.  But 
each  position  of  this  field,  as  a  whole,  is  entirely  determined  by  the 
fact  that  the  customary  muscular  and  tactual  sensations  assure  us 
of  the  posture  of  the  head  with  reference  to  the  rest  of  the  body. 
Such  localization  is  accomplished  chiefly  by  sensations  in  the  neck. 
So  far  as  sight  alone  is  concerned,  the  entire  expanse  of  color-sen- 
sations cannot  be  said  to  be  perceived  as  anywhere  in  space. 

The  "retinal  field"  has  no  clearly  defined  limits,  or  boundary- 
lines  ;  it  may  be  described  rather  as  having  its  expanse  of  sensa- 
tions distinguished  by  a  shifting,  graded  transition  into  a  region  of 
no-sensations.  This  fact  is,  of  course,  due  to  the  constantly  chang- 
ing activity  of  the  nervous  elements  of  the  retina.     Yet  the  sensa- 


424  DATA   OR   MOTIFS    OF  VISION. 

tious  which  are  massed  in  the  foregoing  experience  constitute  a 
true  spatial  expanse  ;  they  are  not  simply  recognized  as  differing 
in  color-tone,  or  brightness  or  intensity  of  effect,  but  as  having  true 
local  distinctions,  and  as  being  aiTanged  into  a  system  of  points  of 
color  and  light  lying  side  by  side.  In  other  words,  the  different 
sensations  do  not  fall  together  in  consciousness  so  as  to  resemble 
the  one  sensation  of  smell  produced  by  irritating  simultaneously  a 
number  of  fibres  of  the  olfactory  nerve  ;  nor  are  they  simply  ana- 
lyzable  into  several  qualitatively  different  factors,  as  is  the  com- 
plex sensation  of  a  musical  clacg.  They  are  presented  as  spatially 
systematized,  as  a  true  perception  of  an  extended  object.  The  "  ret- 
inal field  "  may,  then,  be  said  to  be  extended  in  two  dimensions  ; 
and  the  minima  visibilia  which  compose  it  all  have  local  relations 
to  each  other.  It  cannot  properly  be  said,  however,  to  have  depth 
(as  Stumpf '  and  Hering  '  hold  that  it  does)  ;  for  the  different  col- 
ored points  are  not  projected  as  different  in  distance,  nor  can  we 
be  said  to  look  into  the  colored  space  thus  presented  before  the 
mind.  It  is  true  that  the  expanse  of  the  retinal  field  is  not  like 
that  of  a  darkly  colored  wall  or  curtain  placed  in  front  of  the  eye. 
But  the  quasi-appearance  of  depth  is  due  to  constant  change  in 
color-tone  and  brightness  of  the  minute  portions  of  the  field, 
which  has  an  effect  somewhat  like  that  we  get  on  looking  at  a  very 
dense  mist  of  particles  differently  colored  and  drifting.  In  other 
words,  the  secondary  and  derived  data  give  to  it  an  ajDpearance 
which  we  have  learned  to  associate  with  the  perception  of  depth. 

§5.  Further  experiment,  however,  with  this  so-called  "I'etinal 
field  "  serves  to  show  how  complicated  its  apparently  simple  char- 
acter really  is.  In  the  first  place,  even  this  field  is  the  result  of 
the  combined  action  of  the  two  retinas.  If,  with  both  eyes  closed, 
a  "phosphene  "  (see  p.  195  f.)  be  produced  in  either  eye  by  pressing 
upon  its  ball,  the  colored  circle  will  be  located  in  the  correspond- 
ing part  of  the  field  ;  but  the  character  of  the  entire  field,  as  formed 
by  the  activity  of  both  retinas,  wiU  be  changed.  It  is,  of  course, 
impossible  to  suppress  the  action  of  one  retina,  and  thus  exam- 
ine a  monocular  "  retinal  field,"  as  it  were.  But  it  may  easily 
be  shown  that,  even  in  vision  with  one  eye  open  and  in  motion, 
the  character  of  the  whole  field  of  vision  is  under  the  influence 
of  the  retinal  activity  of  the  closed  eye.  Let  one  of  the  eyes — both 
hitherto  closed  and  motionless — now  be  opened.     Immediately  a 

'  Ueber  d.  physiolog.  Ursprung  d.  Raumvorstellurig.  Leipzig,  1873.  Stumpf 
liolds  that  "Space  is  just  as  originally  and  directly  perceived  as  quality"  (p- 
115). 

2  In  Hermann's  Handb.  d.  Pliysiol,  III.,  1.,  p.  572  f. 


NATURE   OF   THE   RETINAL   FIELD.  425 

picture  of  all  the  objects  falling  within  the  field  of  monocular  vision 
appears  before  us  ;  each  object  seen  with  its  position,  magnitude, 
and  spatial  relations  determined  according  to  the  laws  of  visual 
perception.  This  monocular  field  seems  bounded  on  one  side  (the 
left  side  if  the  right  eye  is  opened,  the  right  side  if  the  left)  by 
the  rather  dim  outline  of  the  nose  and  lower  line  of  the  forehead. 
What  has  become  of  the  retinal  field  of*  the  closed  eye  ?  It  has 
been  submerged  or  overwhelmed  by  the  field  of  the  open  eye,  on 
account  of  the  latter's  stationary  and  clearly  defined  images  and 
strong  arrest  and  fixation  of  attention.  But  if  a  character  to  arrest 
and  fix  the  attention  be  given  to  the  field  of  the  closed  eye,  it  may 
be  made  in  turn  to  overwhelm  that  of  the  open  eje.  This  can  be 
accomplished  by  producing  strong  "  phosphenes  "  in  the  former.  On 
pressing  the  closed  eye  brightly  colored  circles  are  presented  in 
the  corresponding  part  of  the  field  ;  and  by  using  sufficient  press- 
ure the  objects  seen  as  projected  in  space  by  the  open  eye  are 
drowned  in  a  shower  of  minute,  vivid  sparks. 

The  "  retinal  field "  has  its  character  determined  also  by  as- 
sociated muscular  sensations  dependent  upon  the  movement  of 
both  eyes.  It  will  be  found  impossible  to  make  any  definite  area 
of  this  retinal  field,  which  lies  much  to  the  right  or  left,  to  the 
upper  or  lower  part,  of  its  centre,  a  matter  of  regard  without 
detecting  slight  movements  of  the  eyes  according  to  the  direc- 
tion in  which  the  attention  is  to  be  fixed.  The  value  of  muscular 
movements  in  this  case  cannot  consist  in  their  enabling  a  clear 
image  of  objects  situated  in  different  relations  to  the  eye  to  be 
formed  on  its  retina  ;  for  with  closed  eyes  no  change  is  occasioned 
in  the  retinal  images  by  motion  of  the  eyes.  The  conclusion,  then, 
is,  that  certain  muscular  sensations  constitute  an  indispensable 
part  of  the  data  for  localizing  objects  even  in  the  retinal  field — at 
least  such  as  are  only  a  slight  distance  from  its  centre.  Moreover, 
it  will  be  found  that  the  extent  of  this  entire  field  and  its  pro- 
longation, as  it  were,  in  any  given  direction  are  dependent  upon 
the  accommodation  and  motion  of  the  eyes.  The  explanation  of 
this  fact  can  be  found  only  in  the  same  truth,  namely  :  The  per- 
ception of  localized  areas  in  the  tivo-dimensioned  "  retinal  field  "  of  the 
closed  eyes  is  dependent  upon  the  revival  of  associated  muscular  sen- 
sations. 

§  6.  The  foregoing  facts  undeniably  afford  considerable  support 
to  the  "  empiristic  "  theory  of  visual  perception  ;  but  they  do  not 
show  that  the  considerations  it  brings  forward  are  entirely  con- 
clusive. They  do  not  even  prove  the  truth  of  Wundt's  statement :  ' 
'  Physiolog.  Psychologie,  ii.,  p.  69. 


426  DATA   OR   MOTIFS   OF   VISION. 

"  Our  sensations  of  light  do  not  immediately  possess  spatial  form." 
After  excluding  all  the  factors  wliich  combine  into  our  ordinary 
presentations  of  sight — such  as  double  images,  accommodation, 
convergence  of  the  axes  of  the  eyes,  and  secondary  helps  by  way 
of  shadows,  perspective,  elevation,  etc. — a  certain  spatial  quality 
still  remains  to  the  simplest  sensations  of  color  and  light  which 
we  are  able  to  reproduce.  It  will  naturally  be  objected  that  these 
sensations  are  the  reactions  of  a  mind  that  has  had  a  long  pre- 
vious experience  in  localizing  visual  sensations  by  means  of  just 
such  heljDS  as  the  foregoing.  The  question  then  recurs :  Is  the 
fact  that  the  sensations  of  light  and  color,  which  are  produced  by 
the  simultaneous  excitation  of  many  nervous  elements  of  the  ret- 
ina, appear  as  locally  distinct  (even  when  the  eyes  are  closed  and 
motionless)  an  otherwise  unexplained  datum  due  to  an  original 
activity  of  the  mind  under  the  law  of  the  specific  energy  of  these 
nervous  elements  ;  or  is  it  a  result  of  acquired  experience,  to  be 
explained  by  the  revival  of  images  of  previously  associated  impres- 
sions obtained  when  the  eyes  were  both  open  and  moving  ?  To 
take  the  former  position  is  to  adopt,  so  far  forth,  the  nativistic 
theory  of  visual  perception  ;  to  take  the  latter  is  to  espouse  the 
empiristic  opinion.  Either  position  has  its  difficulties.  The  for- 
mer seems  to  us,  however,  nearer  to  the  ultimate  truth. 

§  7.  That  the  sensations  of  light  and  color  occasioned  by  stimu- 
lating different  elements  of  the  retina  have  a  different  value  in 
consciousness,  and  that  the  recognition  of  this  value,  and  the  pres- 
entation of  the  sensations  as  locally  separate  and  arranged  into 
a  spatial  system,  is  native  to  the  mind,  may  be  argued  from  the 
following  among  other  reasons :  The  peculiar  mosaic  structure  of 
the  retina  is  obviously  the  fundamental  cause  for  the  pre-eminence 
of  the  eye  as  a  "  geometrical  sense."  It  has  already  been  shown 
(Chap.  IV.,  §  3)  that  each  element  of  this  structure  maybe  regarded 
as  an  isolated  sensitive  spot,  which  corresponds,  on  the  one  side,  to 
individual  irritations  from  the  stimuli,  and,  on  the  other,  to  the 
smallest  localized  sensations  of  light  and  color.  But  the  latter  part 
of  this  statement  could  not  be  true  unless  each  of  the  elements  in 
this  nervous  mosaic  had  a  certain  peculiar  representative  value  in 
consciousness.  In  other  words,  sensations  of  light  and  color  are 
localized  in  part,  at  least,  by  means  of  the  specific  local  quality 
which  belongs  to  the  result  of  the  different  points  in  the  retina 
being  simultaneously  irritated.  The  very  construction  of  this  or- 
gan, as  well  as  the  correspondence  between  its  construction  and  the 
nicety  attained  in  its  use  for  local  distinctions,  indicates  that  the  spa- 
tial quality  of  our  visual  percepts  depends  upon  its  specific  functions. 


NATURE   OF   THE  RETHSTAL   IMAGE.  427 

Moreover,  unless  the  series  of  light-  and  color-sensations  had  an 
original  spatial  character,  it  is  difficult  to  see  how  they  could  com- 
bine with  the  other  sj)atial  series  of  the  eye  into  percejDtions  of  ex- 
tended colored  objects.  It  is  difficult  to  see  what  advantage  they 
would  then  have  over  the  series  of  musical  tones  varying  in  pitch. 
Still  further,  it  is  as  impossible  to  prove  exj)erimentally  as  it  is  to 
make  seem  true  to  consciousness  that  the  arrangement  of  the  points 
of  light  and  color  which  ajppears  before  us  with  closed  and  motionless 
eyes  is  only  the  residuum,  as  it  were,  of  past  sensations  of  a  muscu- 
lar kind.  Such  an  appeal  to  consciousness  could  not  be  made,  in- 
deed, with  any  confidence,  if  scientific  analysis  were  able  to  show 
that  the  color-sensations  can  be  perceived  simultaneously,  as  a  sys- 
tem of  points  lying  side  by  side,  without  having  the  characteristics 
of  a  spatial  series.  But  in  view  of  our  inability  to  do  this,  we  only 
account  for  the  facts  of  consciousness  by  admitting  what  the  very 
structure  of  the  organ  suggests,  and  what  general  psychological 
theory  seems  to  confirm,  when  we  hold  that  spatial  perception,  at 
least  in  germinal  form,  is  native  to  the  mind  as  a  synthesis  of  the 
qualitatively  different  sensations  which  result  from  stimulating  simul- 
taneously the  retinal  mosaic  of  nervous  elements. 

The  foregoing  view  is  very  different  from  that  which  assumes 
that  we  have  an  immediate  knowledge  of  the  retinal  image  ;  or 
that  a  knowledge  of  the  direction  from  which  the  Hght  falls  upon 
the  retina  is  an  unresolvable  intuition  of  the  mind. '  To  such  mis- 
taken statements  it  is  a  sufficient  reply  to  show  that  the  subjective 
image  (or  mental  presentation)  of  the  object  does  not  correspond 
either  to  the  image  on  the  retina  or  to  the  real  object  as  it  is  other- 
wise known  to  exist  in  space.  The  mental  presentation,  for  exam- 
ple, has  no  blind-spot ;  it  is  a  different  representation  of  the  real 
object  from  that  offered  by  the  retinal  image,  with  more  inaccu- 
racies than  belong  to  the  latter  as  seen  by  an  observer  looking 
at  it  from  without.^  To  the  question,  then,  whether  sensations  of 
light  and  color  would  have  space-form  if  they  came  only  from  an 
excited  but  motionless  retina,  and  were  uncombined  with  other 
sensations  of  a  spatial  series,  we  can  give  only  a  tentative  and  par- 
tial answer.  Doubtless  the  "presentations  of  sense"  formed  by 
combining  such  sensations  alone  would  be  indescribably  different 
from  those  to  which  we  now  ascribe  visual  space-form.  An  animal 
with  a  single  immovable  expanse  of  nervous  elements  susceptible 

'  See  Le  Conte,  Sight,  pp.  85  f.  and  105.  IS'ew  York,  1881.  Le  Conte  is 
obliged  to  admit,  however,  that  this  "  law  of  direction  "  is  sometimes  opposed 
to  the  "law  of  corresponding  points  "  (p.  258). 

'^  See  Wundt,  Physiolog.  Psychologie,  ii.,  p.  68. 


428  DATA   OR   MOTIFS    OF  VISIOTST. 

to  irritations  from  ligM  could  not  be  said  to  have  what  we  call 
"  vision."  But,  on  the  other  hand,  the  spatial  quality  which  be- 
longs to  the  visual  sensations  of  man  cannot  be  all  resolved  into 
muscular  and  tactual  sensations  of  eye  and  hand  ;  these  sensations, 
quoad  sensations  of  light  and  color,  do  have  the  quality  which  in- 
sures their  arrangement  in  consciousness  in  spatial  order.  This 
fact  is  due  to  the  working  of  the  law  of  the  specific  energy  of  the 
nervous  retinal  elements  in  connection  with  the  native  activity  of 
mind  in  synthesizing  these  sensations.  The  law  as  applied  to  the 
eye  is  essentially  the  same  as  that  already  demonstrated  for  the 
skin  ;  the  activity  assumed  as  native  to  man  is  not  essentially  dif- 
ferent from  that  ascribed  to  the  lower  animals  in  the  use  of  their 
senses.  That  this  tact  for  the  individual  has  been  largely  won  by 
the  development  of  the  race  is  a  proposition  to  which  our  attitude 
is  determined  by  more  general  conclusions.  But  physiological  op- 
tics cannot  account  for  the  phenomena  of  vision  without  assum- 
ing both  the  original  exercise  of  this  tact  and  the  theory  of  local 
retinal  signs  as  data  hitherto  uni'esolvable  by  its  analysis. 

§  8.  Whatever  may  be  thought  of  the  foregoing  assumptions,  it 
is  certain  that  ordinary  adult  visual  perception  involves  the  motion 
of  the  open  eye — monocular  vision  of  one  eye  and  binocular  of 
both.  The  sensations  which  accompany  such  motion  must  be  com- 
bined with  sensations  of  light  and  color  to  make  the  complete  pres- 
entations of  sight.  The  consideration  of  the  simplest  case  requires 
that  we  should  recur  to  the  physiology  of  the  eye.  Only  one  small 
spot  in  the  retina  (the  so-called  "fovea  centralis,"  see  p.  183),  is 
capable  of  giving  a  perfectly  clear  image  of  an  object.  When,  then, 
we  desire  to  see  an  object  clearly,  we  bring  its  image  upon  this 
spot  and  fixate  it  there.  That  point  of  the  object  to  which  the 
centre  of  the  retinal  area  of  clearest  vision  corresponds  is  called 
the  "point  of  regard"  (or  "fixation-point").  In  ordinary  vision, 
then,  the  eye  constantly  changes  its  point  of  regard,  and  so  brings 
successively  upon  its  most  sensitive  area  the  images  of  the  different 
points  of  its  object. 

The  different  changes  of  position  in  the  point  of  regard  are 
accompanied  by  sensations  of  motion  and  strain  ;  they  are  accom- 
plished by  the  six  muscles  of  the  eyeball.  This  wandering  of 
the  point  of  regard  over  an  object  may  be  considered  as  accom- 
plished by  rotating  the  eye  vipon  a  pivotal  point,  or  "  centre  of 
rotation,"  by  motions  that  have  different  axes  of  rotation.  The 
centre  of  rotation  is,  however,  only  theoretically  a  point,  but  is 
really  an  interaxial  space.  It  has  been  variously  located  for  normal 
eyes  at  about  13.45-13.73  mm.  behind  the  cornea,  and  1.24-1.77 


PRIMARY   POSITIOIir  OF   THE   EYE. 


429 


pbl.:,SUp. 


mm.  behind  the  middle  of  the  optical  axes.  Of  such  axes  of  rota- 
tion, three  are  especially  to  be  distinguished — an  antero-posterior, 
a  vertical,  and  a  ti-ansverse.  A  line  drawn  from  the  centre  of 
rotation  to  the  point  of  regard 
is  called  the  "line  of  regard;" 
since  each  eye  has  its  own  cen- 
tre of  rotation,  there  are,  in  vi- 
sion with  both  eyes,  two  lines  of 
regard.  A  plane  passing  through 
these  two  lines  is  called  "  the 
plane  of  regard "  (or  "  plane  of 
vision").'  In  the  " primary  posi- 
tion "  the  head  is  erect  and  the 
line  of  regard  directed  toward 
the  distant  horizon.  The  plane 
jDassing  througli  the  lines  of  re- 
gard of  both  eyes  in  this  position 
is  the  "  primary  plane  of  vision." 
In  this  position  for  most  eyes, 
however,  the  line  of  vision  is  in- 
clined somewhat  below  the  hori- 
zontal plane. 

Starting  from  the  primary  po- 
sition, one  set  of  positions  are  suc- 
cessively assumed  by  moving  the  eye  upon  its  transverse  and  verti- 
cal axes.  When  the  eve  rotates  round  the  former,  the  line  of  regard 
is  displaced  either  above  or  below  ;  it  thus  makes  a  varying  angle 
with  the  line  corresponding  to  its  first  direction,  and  this  is  called 
the  "  angle  of  vertical  displacement  "  (so  Helmholtz),  or  the  "  ascen- 
sional angle."  When  it  moves  about  the  vertical  axis,  the  line  of 
regard  is  displaced  from  side  to  side,  and  forms  with  the  median 
plane  of  the  eye  a  varying  angle  called  "the  angle  of  lateral  dis- 
placement." In  passing  from  the  primary  position  to  the  foregoing 
secondary  position  no  rotation  of  the  axis  itself  occurs.  Another 
order  of  positions  is  assumed  by  an  apparent  rotation  on  the  antero- 
posterior axis,  combined  with  lateral  or  vertical  displacements ;  this 
movement  results  in  bringing  the  eye  to  an  oblique  position,  and  is 
really  a  torsion  of  the  eye.  The  angle  which  the  plane  of  regard 
makes  with  the  transverse  plane  measures  the  amount  of  torsion, 
and  is  called  the  "  angle  of  torsion." 

'  For  the  detailed  theory  of  the  movements  of  the  eye,  see  Hering,  in  Her- 
manns  Handb.  d.  Physiol.,  III.,  i.,  chaps.  9-11  ;  Helmholtz,  Physiolog.  Op- 
tik,  §g  27-30  ;  and  Wuudt,  Physiolog.  Psychologic,  ii.,  p.  72  f. 


r>ext;  r.  inf.  r.  int; 


Fig.  97.— Diaprram  of  the  Attachments  of  the 
Muscles  of  the  Eye,  and  of  their  Ajxes  of  Ro- 
tation— the  latter  being  shown  by  clotted 
lines.  The  axis  of  rotation  of  the  rectus, 
externus,  and  internus,  being  perpendicular 
to  the  plane  of  the  paper,  cannot  be  shown. 


430 


DATA   OR  MOTIFS   OF  VISION. 


§  9.  The  various  movements  possible  for  the  eye  in  all  the  direc- 
tions just  described  are  accomplished  by  the  combined  pull  of  the 
muscles  of  the  eye  as  summarized  in  the  following  table  '  (for  the 
muscles  and  their  position,  see  Fig.  49  f.,  p.  174)  : 


Number  of  muscles  active. 

Direction  of  line  of  regard. 

Muscles  acting.. 

n-no 

5  Inward 

Internal  rectus. 

(  Outward 

External  rectus. 

(  Upward 

j  Superior  rectus. 

Two 

{  Downward 

'  Inward  and  upward .... 

Inward  and  downward . . 
- 
Outward  and  upward  . . 

Outward  and  downward. 

I  Inferior  oblique. 

Three 

j  Inferior  rectus. 
I  Superior  oblique, 
I  Internal  rectus. 
•<  Superior  rectus. 
(  Inferior  oblique. 
(  Internal  rectus. 
<  Inferior  rectus. 
(  Superior  oblique. 

i  External  rectus. 
-|  Superior  rectus. 
( Inferior  oblique. 
i  External  rectus. 
■|  Inferior  rectus. 
(  Superior  oblique. 

§  10.  The  law  which  seems  to  govern  all  the  eye's  movements  of 
torsion — or  combined  movements  sideways,  and  either  up  or  down 
—was  conjectured  by  Listing,  whose  name  it  bears,  and  elaborated 
by  Helmholtz.  Listing's  law  is  stated  by  Helmholtz  *  in  the  fol- 
lowing terms  :  "  When  the  line  of  regard  passes  from  its  primary 
position  into  any  other  position,  the  torsion  of  the  eye  (as  meas- 
ured by  the  angle  of  torsion)  in  the  second  position  is  the  same  as 
if  the  eye  were  turned  about  a  fixed  axis  standing  perjDendicular  to 
both  the  first  and  the  second  positions  of  the  line  of  regard."  The 
same  principle  is  stated  in  different  language  by  Wundt  :  ^  "  All 
movements  of  the  eye  from  its  primary  position  take  place  about 
fixed  axes,  each  of  which  at  the  point  of  rotation  stands  at  right 
angles  to  the  plane  which  is  described  by  revolving  the  line  of  re- 
gard ;  and  all  of  these  axes  lie  in  a  single  plane,  at  right  angles  to 
the  primary  position  of  the  line  of  regard,  at  its  point  of  rotation." 
The  orientating  of  the  eye,  then,  for  every  possible  position  of  the 
line  of  regard,  may  be  referred  to  a  constant  standard.  Concerning 
one  important  matter  in  the  carrying  out  of  Listing's  law,  thei-e  is 
a  direct  conflict  of  view  between  authorities.     According  to  Helm- 

'  Given  by  Beaunis,  and  to  be  found  in  the  Encyclopaedia  Britannica, 
ninth  ed.,  VIII.,  p.  825. 

2  Physiolog.  Optik,  p.  466.  ^  Physiolog.  Psychologie,  ii.,  p.  79  f. 


THE  EFFECT   OF   ROTATIOlSr.  431 

holtz,'  when  the  plane  of  vision  is  raised,  lateral  displacements  to 
the  right  produce  rotation  of  the  eye  to  the  left,  and  lateral  dis- 
placements to  the  left  produce  rotation  to  the  right ;  when  the 
plane  of  vision  is  depressed,  lateral  displacements  to  the  right  pro- 
duce rotation  to  the  right,  and  vice  versa.  But  according  to  Le 
Conte,'  in  elevation  of  the  visual  plane  the  eyes  both  move  and  ro- 
tate to  the  right  or  to  the  left  ;  in  depression  of  this  plane,  motion 
of  the  eyes  to  the  light  is  accompanied  with  rotation  to  the  left, 
and  motion  to  the  left  with  rotation  to  the  right. 

More  detailed  statement  of  the  laws  of  the  eye's  motion  in  vi= 
sion  is  not  necessary  for  the  purposes  of  physiological  psychology. 
It  need  only  be  noted  that  the  construction  of  the  field  of  monocular 
or  binocular  vision  is  a  synthetic  mental  achievement  dejoendent  upon 
the  varying  sensations  which  result  from  the  wandering  of  the  point  of 
regard  over  the  outline  of  an  object.  Starting  from  its  primary  posi- 
tion, the  eye  may  come  around,  as  it  were,  by  a  variety  of  circui- 
tous paths,  to  the  fixation  of  any  particular  point  of  its  object.  In 
the  pursuit  of  these  paths  it  develops  various  series  of  muscular 
sensations  that  have  spatial  qualities  and  are  fitted  to  combine  with 
the  spatial  series  of  light  and  color  sensations.  Thus  the  field  of 
vision  necessarily  has  the  same  form  as  the  surface  over  which  the 
point  of  regard  can  be  made  to  wander.  Its  construction  is  a  pro- 
gressive synthesis  of  the  mind,  stimulated  and  guided  by  means  which 
consist  in  varying  states  of  consciousness,  chiefly  dependent  upon 
the  local  coloring  of  the  two  sets  of  sensations  thus  far  described. 

§  11.  Certain  important  consequences  follow  as  to  the  relation 
between  the  lines  of  the  extended  and  objective  "  thing  "  and  the 
lines  of  the  retinal  image,  as  affording  the  mind  data  for  the  spatial 
ordering  of  the  sensations  that  arise  from  stimulating  the  nervous 
retinal  elements  and  nerve-fibres  of  the  muscles  of  the  eye.  Both 
the  general  form  of  the  field  of  vision  and  the  relative  position  of 
the  objects  in  it  are  determined  by  the  movements  of  the  eye.  The 
rule  is,  that  only  those  objects  which  ai-e  seen  by  direct  vision  (their 
images  lying  in  the  line  of  regard  when  the  eye  is  in  its  primary 
position)  appear  in  their  actual  place  ;  objects  indirectly  seen  ap- 
pear in  the  place  which  they  would  assume  if  their  retinal  images 
were  transposed  to  the  point  of  regard  and  its  immediately  sur- 
rounding points.^  It  follows,  furthei',  that  all  lines  lying  outside 
of  the  vertical  and  horizontal  meridians  of  the  retina,  in  order  to  be 
seen  straight,  must  be  really  bent ;  and  all  really  straight  lines  in 

'  Physiolog.  Optik.,  p.  463, 

'•*  Sight,  pp.  173  fE.  ;  and  American  Journal  of  Science  and  Arts,  xx.  (1880), 
pp.  83  ff.  ^  Comp.  Wundt,  Physiolog.  Psjchologie,  ii.,  p.  90  f. 


432  DATA   OR   MOTIFS    OF   VISION. 

such  positions  are  seen  bent.  This  fact  may  be  proved  in  varioua 
ways.  If  a  sheet  of  white  paper,  having  a  black  dot  in  its  centre 
to  serve  as  a  point  of  regard,  be  held  at  right  angles  to  the  line  of 
vision,  with  the  eye  in  its  primary  position  and  constantly  fixed 
upon  this  point,  thin,  straight  slits  of  black  jDaper  outside  of  the  two 
meridians  will  appear  bent.  Or  if  the  after-images  left  on  these 
meridians  of  the  retina  by  light  falling  through  narrow  and  straight 
slits  be  studied  when  torsion  of  the  eye  takes  place,  these  after-im- 


e| ]e 

Fig.  98  (From  HerinR.  after  Helmholtz).— With  the  eye  at  the  distance  e-e,  and  fixated  upon  the 
centre,  the  hyperbolic  lines  which  limit  the  black  and  white  surfaces  show  the  so-called  "right 
lines  "  of  the  field  of  vision. 

ages  will  themselves  be  found  to  suffer  torsion.'  Such  images,  re- 
ceived upon  the  vertical  meridian  of  the  eye  when  it  is  in  its  pri- 
mary position,  lean  to  the  right,  thus  /  ,  when  the  visual  plane  is 
elevated  and  the  eye  moved  to  the  right ;  but  when,  with  this 
plane  elevated,  the  eye  is  moved  to  the  left,  the  vertical  image  in- 
clines to  the  left,  thus    \    .     With  depression  of  the  visual  plane, 

the  inclination  of  the  after-image  is  reversed.     The  image  of  a 

perfect  rectangular  cross  is  distorted  as  follows  by  different  torsions 

>  See  Le  Conte,  Sight,  pp.  164  fE. 


SENSATIOlSrS   OF   ACCOMMODATION.  433 


of  the  eye  :  "Upward  and  to  the  right,  ,J^^  ;  upward  and  to 
the  left,  "^"v,  ;  downward  and  to  the  right,  ^-«\^  ;  down- 
ward and  to  the  left,  .^4'^ »,     The  connected  results  of  all  the 

possible  torsions  of  the  eyes  in  curving  the  lines  of  the  field  of  vis- 
ion is .  illustrated  by  the  accompanying  figure  (98)'  ;  the  study  of 
this  figure,  as  it  appears  at  various  distances,  from  arm's  length  to 
contact  with  the  nose  and  forehead,  is  an  instructive  exercise.  The 
dependence  of  the  field  of  vision  upon  the  positions  and  motions 
of  the  eye  is  one  principal  source  of  the  errors  of  this  sense. 

§  12.  Besides  the  help  from  muscular  sensations  due  to  move- 
ments of  the  eye  in  fixing  its  point  of  regard,  account  must  be  taken 
of  those  which  result  from  accommodation  of  the  eye  (for  the 
mechanism  of  accommodation,  see  p.  177  f.).  As  says  Helmholtz  : " 
"  There  can  be  no  doubt  that  anyone  who  has  much  observed  his 
own  changes  of  accommodation  and  knows  the  muscular  feeling 
of  the  effort  belonging  to  them,  is  in  a  condition  to  tell  whether, 
when  he  fixates  an  object  or  an  optical  image,  he  is  accommodating 
for  a  great  or  small  distance."  There  is  scarcely  greater  doubt  that 
the  significance  of  this  change  of  muscular  feeling  would  not  be 
realized  as  indicating  a  third  dimension  of  space,  were  it  not  com- 
bined with  sensations  belonging  to  the  use  of  both  eyes  in  conjunc- 
tion with  the  organs  of  touch.  Even  adult  judgment  of  distance, 
by  accommodation  alone,  is  extremely  imperfect.  Wundt  ^  experi- 
mented to  determine  the  niceness  of  this  judgment  by  regarding  a 
black  thread,  stretched  vertically  against  a  white  background,  with 
one  eye  through  an  aperture  in  a  shield.  He  found  that  almost 
nothing  could  be  told  in  this  way  as  to  the  absolute  distance  of  the 
thread.  Its  relative  position,  however,  could  be  discriminated  with 
considerable  accuracy  by  changes  in  accommodation  ;  and,  as  might 
be  expected,  with  more  accuracy  when  the  apparatus  was  called 
into  more  active  operation  by  approach  of  the  object  toward  the 
eye.  Helmholtz  *  found  that  he  required  a  stronger  accommoda- 
tion to  see  a  red  stripe  clearly  through  a  tube  than  was  necessary 
to  see  one  of  blue. 

'  Taken  from  Hering  (after  Helmlioltz),  in  Hermann's  Handb.  d.  Physiol., 
ni.,  i.,  p.  537. 

?  Physiolog.   Optik,  p.  633. 

^  Beitrage  zur  Theorie  d.  SiuneswahrnelLmung,  1863,  pp.  105-118. 
4  Ibid.,  p.  634. 
28 


434 


BINOCULAR   FIELD   OF   SIGHT. 


§  13.  But  all  tlie  achievements  possible  to  a  single  eye,  when  open 
and  in  motion,  would  not  avail  to  produce  the  presentations  of 
sight  as  our  ordinary  experience  is  familiar  with  them.  Strictly 
monocular  vision  is  for  the  most  part  a  fiction  of  science.  What 
we  can  see  with  one  eye,  after  experience  in  binocular  vision,  de- 
pends upon  what  we  have  been  accustomed  to  see  with  both  eyes. 
Indeed,  what  we  see  at  any  instant  with  one  open  eye  depends,  in 
part,  upon  the  position,  motion,  and  retinal  condition,  of  the  other 
and  closed  eye.  A  theory  of  hinocular  vision,  however,  requires  the 
consideration  of  two  sets  of  data  in  addition  to  those  already  enumer- 
ated. These  are  the  existence  and  relations  of  the  two  retinal  images, 
and  the  relations  and  laws  of  the  binocular  movements  of  the  eyes. 
The  fact  that  two  eyes  are  ordinarily  active,  and  that  there  are, 
therefore,  two  images  of  the  object,  is  a  fact  of  the  first  importance 
for  the  theory  of  visual  percej^tion.  Each  eye  is  in  itself,  indeed, 
a  complete  optical  instrument ;  each  has  its  own  point,  line,  and 
plane  of  regard,  and  movements  of  rotation,  torsion,  and  accom- 
modation. The  two  eyes,  however,  act  normally  as  one  instrument ; 
and  yet  they  cannot  be  regarded  as  mere  duplicates.  The  theory 
of  binocular  vision,  then,  considers  the  two  eyes  acting  as  one.  For 
the  purposes  of  such  theoz-y  it  is  not  important  what  shape  the  two 

retinas  are  regarded  as  having ; 
they  are  usually  taken  as  surfaces 
with  the  curvature  of  the  inside 
of  a  sphere  whose  centre  lies  at  a 
point  where  all  the  lines  of  direc- 
tion intersect. '  It  may  be  assumed, 
to  begin  with,  that  this  point  of  in- 
tersection is  the  same  for  accom- 
modation to  all  distances  of  the 
object.  If  the  two  retinas  were 
perfectly  symmetrical  all  the  ner- 
vous elements  which  compose  the 
mosaic  of  each  one  might  be  re- 
garded as  situated  at  points  identi- 
cal with  those  occupied  by  the  ner- 
vous elements  of  the  other.  In 
other  words,  the  surfaces  of  the 
two  retinas  might  be  regarded  as  capable  of  being  perfectly  super- 
imposed. Upon  such  retinas,  when  the  eyes  Avere  parallel,  each  sin- 
gle point  of  an  object  would  have  its  image  formed  upon  two  "  iden- 

^  See  Hering,  Plijsiolog.  Optik,  in  Hermann's  Handb.  d,  Physiol. ,  IH.,  1.,  p. 
349  f. 


Fig.  99. — Diagram  to  illustrate  the  theory 
of  corrosponding  retinal  points.  The  im- 
ages rif  objects  at  a"  or  b"  or  c"  will  fall 
on  forrfsponding  points  of  the  retina— 
a  and  a',  b  and  b',  c  and  c' — and  be  seen 
Bingle. 


IDE]^TICAL   AND   CORRESPONDING   POINTS.  435 

tical "  points  of  the  two  retinas — upon  points,  that  is,  wliose  position 
would  be  mathematically  the  same  with  relation  to  the  centre  of 
each  retina. 

But  the  retinas  are  not  symmetrical,  and  the  physiological  centre 
is  not  the  true  mathematical  centre  ;  moreover,  the  eyes,  to  be  of  use, 
must  act  together  in  other  positions  than  that  called  "  primary."  A 
distinction  must  then  be  made  between  corresponding  points  and 
identical  points  ;  the  former  are  such  as  are  found  by  experiment 
actually,  as  a  rule,  to  act  together  and  to  combine  their  images 
when  simultaneously  stimulated.  If  the  eyes  be  fixated  upon  any 
very  remote  object  without  apparent  magnitude — for  example,  a 
star— the  points  of  two  retinas  upon  which  its  image  falls  when  it 
is  seen  as  single  are  "  corresj)onding."  One  image  then  exactly 
covers  the  other.  But  in  certain  cases  the  j)oints  of  the  retinas 
which  customarily  act  together  do  not  so  act ;  points  not  exactly 
corresponding  sometimes  cover  each  other,  and  points  usually  cor- 
responding sometimes  fail  to  cover  each  other.  Hence,  a  distinc- 
tion may  be  made  between  corresponding  points  and  "  covering 
points  ; "  the  latter  term  being  used  for  those  points  whose  im- 
pressions, in  each  individual  case  of  seeing,  are  actually  referred  to 
one  and  the  same  point  of  the  object'  The  two  points  of  regard  of 
the  two  eyes  are  in  all  cases  identical,  corresponding,  and  cocering. 

Scarcely  more  than  a  reference  to  previous  elaborate  attempts  to 
determine  the  corresponding  points  of  the  two  retinas  is  necessary 
for  our  purpose.'^  Experiment  shows  that  considerable  reciprocal 
substitution  takes  place  among  the  diffei'ent  points  of  both  retinas. 
The  eyes  of  most  persons,  if  not  of  all,  are  both  structural!}'  and 
functionally  incongruous.  When  the  lines  of  regard  lie  parallel  in 
the  plane  of  the  horizontal  meridian  of  the  two  retinas,  the  verti- 
cal meridians  do  not  correspond.  A  vertical  meridian  of  the  left 
eye,  with  its  upper  end  inclined  to  the  left,  may  be  conjoined  with 
a  vertical  meridian  of  the  right  eye  that  has  its  upper  end  inclined 
at  about  the  same  angle  to  the  right.  The  image  of  a  line  which 
lies  on  these  meridians  thus  inclined,  appears  in  the  vertical  horizon 
of  the  field  of  vision  and  divides  it  into  a  right  and  a  left  half. 

§  14.  That  objects  are  ordinarily  seen  as  single  when  their  images 
are  formed  on  corresponding  points  of  the  retinas,  and  otherwise  as 
double,  may  be  shown  by  many  familiar  experiments.''     If  we  hold 

'By  Wundt,  Physiolog.  Psycliologie,  ii.,  p.  122  f. 

^Here  see  Hering,  in  Hermann's  Handb.  d.  Physiol.,  III.,  i.,  pp.  355  ff. ; 
and  Helmlioltz,  Physiolog.  Optik,  pp.  695  ff. 

•'See,  especially,  the  ones  described  by  Le  Conte  (Sight,  pp.  92  fp.),  from 
which  the  immediately  foUowiug  are  taken. 


436 


BINOCULAR   FIELD    OF   SIGHT. 


a  finger  before  the  eyes  and  look,  not  at  it,  but  at  the  wall  or  the 
sky  ;  or  if- we  point  it  at  some  distant  object,  and  keep  ovir  eyes 

steadily  fixed  on  the  object — tAvo  trans- 
parent images  of  the  finger,  rather  than 
one  solid  finger,  will  be  seen.  Many 
persons  may  have  difficulty  in  seeing 
the  two  images,  but  none  will  fail  to  lao- 
tice  their  transparent  character.  Under 
these  circumstances  the  wall,  sky,  or 
distant  object,  may  readily  be  seen 
through  the  finger.  By  experimental 
methods  the  images  of  a  siugle  object 
may  be  dissociated,  and  Avhat  is  really 
one  be  seen  as  two  ;  on  the  other  hand, 
images  coming  from  two  objects  may 
be  combined  upon  corresponding  points, 
and  thus  what  is  really  two  be  seen  as 
one.  It  needs  only  a  little  skilful  press- 
ure upon  one  eyeball  to  create  for  us 
the  double  of  each  one  of  a  group  of 


Fig.  100. — Diagram  to  illustrate  phe- 
nomena of  double  vision.  If  the 
imase  of  the  point  6  fall  in  one  eye     <•   ■        -,  n     ,  in  j  •    ti 

on  6,  and  in  the  other  on  7,  the  dis-   tneuds,  and  to  See  oue  body  jDartially 

tance  of  the  two  images   seen  will     ,i  „i      i.i,„    j.„„ „„j.    ;  ^  „    .„       £ 

equal  that  between  6  and  7.   If  th.,  through  the  transparent  nnage  of  an- 

image  of  a  fall  on  5  and  5.  it  will  be    ^fl-,Q-|»        Tf 
Been  single,  but  if  the  image  of  6  f nil     ^  ^^^•'-  •       -'■■'■ 
on  the  left  eye  at  6,  and  on  the  right 
eye  at  4,  it  will  appear  double. 


two  objects  very  similar — 
for  example,  the  two  forefingers — be 
held  a  little  way  apart  at  about  a  foot 
distant  and  against  a  clear  sky,  three  like  objects,  one  solid  and  two 
transparent,  may  be  made  to  appear  by  combining  the  two  middle 
images  and  dissociating  the  two  on  the  outside.  Two  systems  of 
regularly  recurring  similar  objects — such  as  a  regular  small  pattern 
of  carpet  or  wall-paper,  or  the  diamond-shaped  spaces  of  a  wire- 
grating— may  have  all  their  images  combined  by  slipping  them,  as 
it  were,  simultaneously  to  one  side.  There  is,  then,  a  double-seeing 
of  what  is  really  single  and  a  single-seeing  of  what  is  really  double  ; 
but  the  latter  is  much  rarer  than  the  former,  and  seldom  occurs 
except  when  brought  about  for  purposes  of  experiment. 

§  15.  It  is  obvious  that  the  relations  of  the  two  images  of  an  ob- 
ject cannot  remain  unchanged  when  the  ej'es  are  moved  from  their 
primary  position.  When  the  eyes  are  converged  upon  an  object, 
the  images  which  are  formed  on  the  central  sj)ots  of  the  two  retinas, 
by  rays  coming  from  the  point  of  regard,  are  exactly  identical  and 
corresponding ;  the  object  in  this  case  is  therefore  seen  absolutely  sin  - 
gle.  Points  of  the  object  lying  near  to  the  jioint  of  regard  in  any  di- 
rection, and  thus  having  their  images  formed  close  to  the  centres  of 


CALCULATION  OF  THE  HOROPTER. 


4G7 


the  two  retinas,  are  also  seen  single.  For  the  points  of  the  retinas 
on  which  the  images  are  then  formed,  although  not  strictly  identi- 
cal, are  corresponding ;  that 
is,  they  have  habitually  act- 
ed together  in  seeing  ob- 
jects single  by  binocular 
vision,  and  the  sHght  incon- 
gruousness  of  the  two  sets 
of  images  is  disregarded,  as 
it  were,  by  the  mind.  But 
all  objects  lying  nearer  or 
Jaaore  remote  than  the  point 
fixated  by  the  eyes  are  liable 
to  be  seen  double  ;  for  their 
images  do  not  fall  on  corre- 
sponding points  of  the  re- 
tinas. Objects  lying  below 
or  above,  or  to  one  side  or 
the  other,  of  the  point  of 
regard,  do  not,  as  a  rule, 
have  their  images  formed  on 
corresponding  points ;  they 
may,  therefore,  also  be  seen 
double.  Some  of  these 
points,  however,  which  oc- 
cupy   positions    below    or 

above,  to  the  one  side  or  the  other,  of  the  point  of  regard,  are  seen 
single.  The  sum  of  all  the  points  which  are  seen  single  while  the 
point  of  regard  remains  the  same  is  called  the  horopter. 

There  has  been  a  great  amount  of  calculation,  experiment,  and 
discussion,  to  determine  the  exact  nature  of  the  horopter.  It  has 
been  held  to  be  a  surface  (plane  or  curved),  a  circle,  a  line,  a  num- 
ber of  disconnected  points.  Its  calculation  as  a  matter  of  mathe- 
matics is  unsatisfactory,  for  the  really  corresponding  points  of  any 
two  retinas  are  not  to  be  determined  by  mathematics.  Experiment 
is  made  exceedingly  difficult  by  the  indistinctness  with  which  we 
see  objects  that  do  not  lie  near  the  point  of  regard.  No  conclusions 
regarding  the  nature  of  the  horopter  are,  perhaps,  on  the  whole, 
more  trustworthy  than  Meissner's.'  They  are  thus  summarized  by 
Le  Conte.'^     With  the  eyes  in  the  primary  position,  the  horoj)teris 

'  Beitrage  zur  Physiologie  d.   Seliorgans,  Leipzig,  1874 ;  and  Arcliives  des 
Sciences,  iii.  (1858),  p.  160  f. 
2  Sight,  p.  204. 


Fig.  101  (From  Hering).— //,  the  sash  of  the  window, 
and  p  the  black  spot  fixated.  On  the  left  line  of 
vision  I  b  lies  a  distant  object,  and  on  the  right  line 
r  e  another  object.  The  images  of  6  and  e,  as  well 
as  the  image  of  ?J,  fall  on  the  place  of  direct  vision 
and,  therefore,  on  corresponding  points  of  the  two 
retinas. 


438  BIlSrOCULAK   FIELD    OF    SIGHT. 

a  plane  perpendicular  to  the  median  line  of  sight.  For  all  nearer 
points  in  the  primary  plane,  it  is  a  line  which  dips  toward  the  ob- 
server with  an  inchnation  to  the  visual  plane,  increasing  with  the 
nearness  of  the  point  of  regard.  When  the  plane  of  vision  is  turned 
upward,  the  inclination  of  the  horopteric  line  increases ;  when  the 
plane  is  turned  downward,  the  inclination  of  the  line  decreases 
until  it  becomes  zero  at  45°,  and  the  line  expands  into  a  plane. 
The  plane  of  the  horopter,  then,  passes  through  the  point  of  regard 
perpendicular  to  the  median  visual  line.  With  these  conclusions 
the  careful  experiments  of  Le  Conte  himself  correspond  in  the 
main  ;  but  Le  Conte  considers  that  the  inchnation  of  the  horopteric 
ILae  remains  constant,  and  that  its  surface,  when  the  horopter  be- 
comes a  surface,  is  curved  instead  of  a  plane. 

§  16.  The  existence  and  relation  of  the  two  images  in  binocular 
vision  is  of  the  greatest  importance  for  all  perception  of  solid 
objects  set  at  varying  distances  from  each  other.  It  is  largely  by 
their  help  that  binocular  perspective  and  stereoscopic  vision  are 
explicable.  But  all  such  elaborate  and  complex  presentations  of 
visual  sense  require  for  understanding  them  certain  considerations 
concerning  binocular  movements  of  the  eyes.  In  binocular  move- 
ments the  laws  of  parallel  motion  hold  good  only  for  the  case  when 
the  eyes,  being  in  the  primary  position,  are  both  turned  equally  in 
the  same  direction.  But  in  fixating  the  point  of  regard  for  the  two 
eyes  for  a  near  object  the  eyes  move  in  opposite  directions,  so  that 
the  lines  of  vision  may  converge  upon  the  object.  In  convergence 
the  eyes  rotate  on  the  optic  axis  in  opposite  dii-ections. '  Since 
divei-gence  of  the  eyes  in  visual  activity  is,  in  all  ordinary  cases, 
impossible,  there  ai-e  three  customary  indissoluble  conjunctions  of 
motion  which  belong  to  the  eyes  as  under  control  from  the  central 
nervous  organism  ;  these  are,  right  and  left  together,  up  and  down 
together,  or  turning  symmetrically  inward.  In  lowering  the  plane 
of  vision,  as  well  as  in  fixating  the  point  of  regard  upon  near 
objects,  convergence  naturally  takes  place  ;  in  elevating  this  plane 
or  in  looking  upon  distant  objects,  the  converging  Hues  of  regard 
diverge  toward  a  parallel  position.  Convergence  may  be  "  sym- 
metrical" or  "  asymmetrical ;"  in  the  former  case  the  two  lines  of 
regard  are  turned  inward  at  equal  angles  and  the  point  of  regard 
is  kept  in  the  median  plane  of  vision  ;  in  the  latter  case  the  point 
of  regard  is  outside  of  the  median  plane,  and  either  the  two  eyes  are 
turned  at  unequal  angles  inward,  or  else  one  is  turned  inward,  and 
the  other,  at  a  smaller  angle,  outward.  Both  kinds  of  convergence 
are  possible  at  different  angles  of  the  elevation  of  the  plane  of  visio/x 
>  See  Le  Conte,  Sight,  p.  178  f. 


THE   USTFLUENCE   OF   ATTENTION.  439 

Listing's  law  does  not  hold  for  movements  of  the  eyes  in  conver- 
gence. '  The  principal  points  at  which  this  law  is  abrogated  for 
converging  motion  of  the  eyes  are  stated  thus  by  Le  Conte  :^ 
When  the  right  eye  moves  to  the  left  in  convergence,  it  rotates  to 
the  right  instead  of  to  the  left  as  in  parallel  motion  ;  so  the  left  eye 
rotates  to  the  left  when  turning  inward.  Whereas  in  parallel  mo- 
tion the  torsion  of  the  eye  increases  with  the  angle  of  the  depres- 
sion of  the  plane  of  vision,  in  convergent  motion  it  decreases  to 
zero  at  45°.  These  facts  doubtless  result  in  imparting  variety  of 
local  coloring  to  those  sensations  of  strain,  etc.,  which  are  produced 
in  the  two  kinds  of  motion  of  the  eyes,  and  which  serve  the  mind 
as  local  signs  in  its  synthesis  of  extended  visual  objects. 

Changes  of  accommodation  naturally  accompany  the  changing 
convergence  of  the  eyes  for  near  objects,  and  the  resulting  sensa- 
tions enter  into  the  spatial  series  out  of  which  the  presentations  of 
visual  sense  are  constructed.  In  the  alteration  of  the  indices  of  re- 
fraction, and  in  the  contraction  of  the  pupils,  the  ej'es  act  together 
under  the  influence  of  motor  impulses  from  the  central  nervous 
organs. 

§  17.  An  effort  to  see,  and  a  corresponding  fixation  of  the  atten- 
tion upon  the  object  lying  at  the  point  of  regard,  are  implied  in 
the  convergence  of  the  eyes.  The  eyes  of  new-born  children  and 
eyes  that  are  recently  couched  after  long-continued  blindness  move, 
as  a  rule,  in  parallel  lines.  ^  .  Ai-rest  of  attention  brings  the  two 
eyes  into  use  as  one  organ,  and  this  necessitates  the  turning  of  the 
lines  of  vision  of  both  so  that  they  shall  meet  at  a  common  point 
where  lies  their  common  object.  It  follows,  also,  that  the  sensa- 
tions accompanying  innervation  of  their  muscles  so  as  to  produce 
convergence  are  of  capital  importance  in  the  construction  of  the 
most  elaborate  and  intelligent  visual  presentations.  According  to 
Wundt,  these  "  feelings  of  innervation  "  are  the  direct  expression 
in  consciousness  of  the  cerebral  changes  that  accompany  the  initiat- 
ing of  motor  impulses  in  the  central  organs.  They  differ  only  in 
intensity  or  amount.  It  is  by  the  "  feeling  "  of  this  amount,  as  it 
were,  that  our  knowledge  of  the  size  and  distance  of  the  object 
seen  in  convergence  is  obtained.  Wundt's  view*  of  the  nature  and 
origin  of  the  feelings  of  innervation,  however,  is  unsatisfactory. 

In  the  opinion  of  Hering,^  the  innervation  of  both  eyes  is  equal, 

^  Comp.  Hering,  in  Hermann's  Handb.  d.  Physiol.,  III.,  i.,  p.  497  1;  and 
Le  Conte,  Sight,  pp.  177  ff.  *  Sight,  p.  190. 

^  Comp.  Bonders  in  Pfliiger's  Archiv,  xiii.,  p.  383. 
*  See  Physiolog.  Psychologie,  ii.,  p.  118  f. 
"  Phvsiolog.  Optik,  Hermann's  Handb.  d.  Physiol.,  III.,  i.,  p.  519  f. 


440  BTNOCULAH   FIELD   OF   SIGHT. 

however  they  are  moved  with  relation  to  each  other.  Even  when 
the  movements  of  the  two  are  unequal,  the  law  holds  ;  for  each  eye 
is  then  under  the  influence  of  two  innervations,  one  of  which  is 
directed  toward  turning  both  eyes  right  or  left,  and  the  other 
toward  turning  them  inward  or  outward.  As  a  result,  in  one  eye 
the  two  innervations  would  support,  and  in  the  other  eye  oppose, 
each  other — thus  bringing  about  a  compensation.  In  this  way  the 
will  guides  its  pair  of  borses  in  either  direction  by  a  pull  upon  one 
rein.  The  innervation  for  accommodation  is  also  supposed  to  be  in 
like  manner  bilateral  and  uniform.  Whatever  view  may  be  taken 
of  the  foregoing  theories  as  to  the  distribution  of  central  innerva- 
tion to  the  two  eyes  and  as  to  the  origin  of  so-called  "feelings  of 
innervation,"  there  can  be  no  doubt  that  the  mental  representatives 
of  the  different  areas  passed  over  and  positions  reached,  in  both 
parallel  and  converging  motions,  are  important  factors  in  construct- 
ing the  presentations  of  sight. 

§  18.  By  the  various  helps  already  described,  stereoscopic  vision 
and  the  seeing  of  things  in  perspective  are  made  possible.  To  one 
eye  acting  alone  and  without  previous  experience,  only  one  of  the 
spatial  series  possible  could,  in  any  event,  serve  as  a  suggestion  of 
depth  ;  this  is  the  series  of  muscular  sensations  accompanying  the 
accommodation  of  the  eye  to  near  distances.  How  little  such  sen- 
sations of  themselves  can  accomplish,  even  at  the  end  of  years  of 
experience  in  binocular  vision,  the  experiments  of  Wundt  make 
obvious  (already  alluded  to,  p.  433).  Our  localization  of  objects 
by  one  eye,  with  respect  to  the  third  dimension  of  space,  is  con- 
fessedly very  imperfect  even  under  the  best  of  circumstances.  It 
is  probable,  then,  that  the  field  of  monocular  vision  is  directly 
known  only  as  a  plane,  and  that  all  immediate  perception  of  depth 
depends  upon  the  existence  of  double  images  and  muscular  sen- 
sations derived  from  the  movements,  especially  in  convergence,  of 
the  two  eyes. 

The  stereoscopic  and  perspective  vision  which  takes  place,  with 
apparent  immediateness,  even  when  one  eye  is  closed,  is  therefore 
really  mediate  and  indirect ;  it  is  accomplished  solely  by  second- 
ary means  of  varying  intensities  of  light  and  color,  changes  in 
apparent  magnitude,  etc.,  on  the  basis  of  associations  gained  by 
using  both  eyes  and  the  hand.  Accordingly,  it  is  easy  to  reduce 
all  the  objects  seen  in  the  field  of  monocular  vision  to  one  depth — 
to  flatness  outlined  on  the  same  plane — by  cutting  off  these 
secondary  helps  and  withdrawing  attention  as  much  as  possible 
from  the  influence  of  judgment  based  on  experience.  By  nearly 
closing  one  eye  while  the   other  is   wholly  shut,   objects   really 


THE    PERCEPTION   OF    DISTANCE.  441 

situated  at  different  distances  from  the  head  may  easily  be  made 
to  appear  as  patches  of  Hght  and  color  blended,  indistinguishably 
to  the  visual  perception,  with  other  patches  of  the  retina's  own 
light.  That  is  to  say,  when  the  results  of  experience  in  interjiret- 
ing  the  secondary  signs  of  the  third  dimension  are  Avithdrawn,  the 
field  of  monocular  vision  becomes  as  purely  two-dimensioned  as  is 
the  "retinal  field." 

§  19.  There  is  no  doubt  that  the  double  images,  and  the  muscu- 
lar sensations  resulting  from  binocular  movement,  furnish  motifs 
for  the  immediate  perception  of  the  distance  and  solidity  of  ob- 
\ects.  In  other  words,  these  two  spatial  series  are  most  important 
data  for  constructing  visual  presentations  of  objects  having  the 
♦hird  dimension.  It  is  more  doubtful  just  how  this  service  is 
rendered.  Stereoscoj^y  has  made  the  fact  familiar,  that  the  two 
images  of  each  object  are  different  as  furnished  by  the  two  eyes.' 
The  right  eye  sees  the  object  farther  around  on  its  right  side,  the 
left  eye  on  its  left.  Every  small  portion  of  a  solid  object,  as  seen 
in  binocular  vision,  provided  it  lies  a  little  way  out  of  the  point  of 
regard,  instead  of  consisting  of  two  exactly  similar  sets  of  lines 
which  might  be  superimposed,  consists  of  two  sets  of  minute 
curves  that  are  partial  images  of  its  lines  and  are  different  for  each 
eye.  The  constant  and  uniform  objects  of  sense  which  appear 
through  the  use  of  both  eyes  result,  therefore,  from  uniting  a  great 
number  of  varying  partial  images  of  these  objects  due  to  simul- 
taneous excitation  of  both  retinas.  In  some  manner  or  other  the 
perception  of  solidity  is  substantially  aided  by  the  combination  of 
these  partial  images. 

Furthermore,  in  ordinary  binocular  vision,  our  perception  of  the 
solidity  and  distance  of  objects  is  accomplished  largely  by  motion 
of  the  eyes  which  successively  unites  and  separates  the  double  im- 
ages of  the  objects  seen.  In  viewing  all  objects  of  any  size,  whether 
near  or  distant,  we  may  readily  become  conscious  of  the  fact  that 
we  are  engaged  in  sweeping  over  the  field  of  vision  with  a  moving- 
point  of  regard.  Even  when  we  suppose  the  eye  to  be  looking  at  a 
single  point,  with  a  perfectly  fixed  regard,  it  is  actually  making 
short  and  rapid  excursions  in  one  direction  and  another  around 
this  point.  How  difficult  it  is  to  keep  the  organ  of  vision  perfectly 
motionless,  anyone  knows  who  has  tried  to  hold  steady  one  of  the 
floating  specks  {musccB  volitantes)  situated  in,  and  projected  in  the 

1  For  the  study  of  the  theory  of  stereoscopy  as  a  matter  of  optics,  the  reader 
is  referred  to  treatises  on  this  science  ;  a  brief  allusion  to  the  fact  is  enough 
for  our  purpose,  which  primarily  is,  of  course,  to  illustrate  the  psychology  of 
visual  perception. 


442  BINOCULAE  FIELD    OF   SIGHT. 

air  before,  this  organ.  Such  facts  strengthen  the  theory  of  Briicke  ^ 
and  others,  that  we  gain  our  perception  of  depth  by  running  the 
point  of  regard  back  and  forth  with  a  varying  degree  of  convei'- 
gence  to  the  axes,  and  so  combining  successively  the  different  parts 
of  the  two  pictui-es  as  seen  by  the  two  eyes. 

But  that  motion  is  not  necessary  for  stereoscopic  vision  with 
adult  eyes  is  proved  by  what  is  known  as  "  Dove's  experiment." 
A  field  composed  of  different  solid  objects  stationed  at  different 
distances  in  space,  or  of  two  stereoscopic  pictures,  may  be  seen  in 
perspective  when  illuminated  by  the  light  of  an  electric  spark. 
Since  the  duration  of  this  spark  is  perhaps  not  more  than  jjiluJ 
sec,  it  is  plain  that  no  change  of  convergence,  or  running  back  and 
forth  of  the  point  of  regard,  has  time  to  take  place.  It  is  asserted 
by  Le  Conte  ^  that  the  interpretation  of  the  double  images  depends 
upon  the  fact  that  such  images  of  any  object  are  different  according 
as  the  object  lies  nearer  or  more  remote  than  the  point  of  regard. 
In  the  latter  case,  the  double  images  are  called  "homonymous," 
and  are  united  by  less  convergence  ;  in  the  former  case  they  are 
called  "  heteronymous,"  and  are  united  by  greater^  convergence  of 
the  optic  axes.  Now  the  observer  knows,  "instinctively  and  xvithout 
trial"  whether  greater  or  less  optic  convergence  will  be  necessary 
to  unite  the  double  images  ;  and  accordingly  refers  the  homony- 
mous images  to  objects  beyond,  the  heteronymous  images  to  objects 
this  side  of,  the  point  of  regard.  But  the  question  arises,  Hoio  does 
this  so-called  "  instinctive  "  knowledge  come  ?  It  can  scarcely  be 
by  way  of  a  native  insight  into  the  distinction  between  homony- 
mous and  heteronymous  images,  as  such  ;  or  through  any  seeing  of 
both  retinal  images  by  the  mind's  eye,'  as  it  were.  Since  what  is 
needed  to  unite  the  images  is  motion  of  the  eye,  and  since  the 
mind  has  always  been  accustomed  to  associate  sensations  of  motion 
with  the  double  images  of  binocular  vision,  it  is  impossible  to  avoid 
the  conclusion  that  instantaneous  binocular  vision,  like  monocular 
vision,  of  solidity  and  distance,  is  secondary  and  wholly  dependent 
ui^on  previous  experience  acquired  with  both  eyes  in  motion. 

§  20.  Localizing  of  the  third  dimension  is,  accordingly,  much 
more  secure  in  binocular  than  in  monocular  vision  ;  and  judgments 
of  distance  are  assisted  greatly  by  movements  of  both  eyes.     If 

'  Archives  des  Sciences,  iii.  (1858),  p.  142. 

2  Sight,  p.  151  ;  and  Am.  Journal  of  Science  and  Arts,  ii.,  1871,  p.  425. 

^  To  say  that  "each  eye,  as  it  were,  knows  its  own  image,  although  such 
knowledge  does  not  emerge  into  distinct  consciousness,"  is  in  plain  contradic- 
tion with  all  the  fundamental  laws  which  psychology  has  to  propound  con- 
cerning the  nature  of  visual  perception. 


INTERPEETATIOlSr   OF   DOUBLE   IMAGES.  443 

no  other  motif  iov  seeing  depth  of  space  is  present,  according  to 
Hering  '  the  following  law  seems  to  hold  :  All  the  lines  or  points 
whose  images  lie,  with  a  given  position  of  the  point  of  regard,  in  the 
vertical  horopter,  appear  clearly  defined  on  a  surface  which  is  either 
plane  or  slightl}'  cylindrical,  and  all  the  lines  or  points  Ijing  this 
side  of  the  surface  of  the  vertical  horopter  and  whose  images  have 
a  "  crossed  disparateness"  (that  is,  the  left  one  of  the  double  im- 
ages belongs  to  the  right  eye,  and  the  right  one  to  the  left  eye — 
making  them  "  heteronymous "),  appear  in  front  of  the  surface  ; 
while  those  lying  beyond  the  horopter  and  whose  images  have  an 
"  uncrossed  disparateness  "  (that  is,  the  right  image  belongs  to  the 
right  eye,  and  the  left  image  to  the  left  eye — making  them  "  hom- 
onymous "),  appear  behind  the  surface  on  which  whatever  lies  iu 
the  horopter  is  seen.  But,  as  we  have  already  learned,  interjDreta- 
tion  of  the  double  images  for  the  stationary  eyes  is  an  acquired  art, 
which  is  dependent  upon  previous  association  of  the  retinal  signs 
of  both  eyes  with  muscular  sensations  arising  from  the  innervation 
and  movement  of  the  eyes.  It  is  also  in  perfection  of  practice  de- 
pendent, as  all  stereoscopic  vision  is,  upon  the  so-called  "second- 
ary "  means  of  such  vision. 

§  21.  All  stereoscopic  vision,  or  vision  of  perspective  for  remote 
objects,  requires,  in  order  to  secure  any  considerable  accuracy,  the 
larger  use  of  "  secondary  helps."  Five  or  more  classes  of  such  helps 
may  be  mentioned.  Vision,  as  accomplished  by  such  means,  is 
often  called  judgment  in  distinction  from  immediate  percej^tion. 
This  should  not  be  held  to  imply  that  activity  of  the  mind  in  as- 
sociation and  discernment  is  not  involved  iu  all  the  jDresentations  of 
sense.  The  distinction  lies  between  such  a  synthesis  of  the  sensa- 
tions into  objects  of  sense  as  is  inseparably  connected  with  all  nor- 
mal binocular  vision,  and  such  other  seeing  (or  judging)  of  the  spa- 
tial properties  and  relations  of  remote  objects  as  depends  for  its 
accuracy  upon  changing  aspects  of  these  objects.  The  increased 
necessity  for  secondary  helps  when  the  objects  of  vision  are  remote 
arises  largely  from  the  fact  that  the  mind  loses  the  data  (or  motifs) 
that  accompany  strong  convergence  and  accommodation  of  the  nor- 
mal eye  for  near  objects.  Changes  in  the  tone  and  intensity  of  the 
muscular  sensations  are  comparatively  slight  on  passing  from  vision 
of  objects  20  40  feet  distant  to  vision  at  infinite  distance.  On  the 
contrary,  such  changes  are  relatively  great  on  converging  the  eyes 
to  alter  the  point  of  regard  from  a  distance  of  20-40  feet  to  one 
of  5-6  inches  ;  still  greater  on  increasing  the  convei'gence  for  still 
nearer  vision.  Hence  the  increased  necessity,  iu  vision  of  distant 
'  Physiolog.  Optik,  Hermanns  Handb.  d.  Physiol.,  III.,  i.,  400  f. 


444 


BINOCULAR   FIELD    OF    SIGHT. 


objects,  for  other  secondary  lielps  to  take  the  place,  as  it  were,  of 
the  diminished  value  of  the  primary  data  or  mot 'fa  of  the  eye. 

§  22.  The  principal  secondary  helps  of  stereoscopic  vision  and 
vision  of  perspective  are  the  following : '  The  course  of  the  Jimitivg 
lines  of  the  objects  in  the  field  of  vision  determines  our  perception 
of  their  distance  and  form  as  lying  in  the  third  dimension  of  space. 
In  looking  at  a  building,  we  connect  together  into  vertical,  horizon- 
tal, or  curved  wholes,  the  successive  fragments  of  the  images  of  its 
lines  as  the  eyes  are  swept  along  in  the  requisite  directions.  If 
these  lines  become  confused  in  distinctness,  or  changed  into  direc- 
tions that  are  contrary  to  our  previous  experience  of  how  the 
parts  of  a  building  appear  to  the  eye,  we  are  liable  to  errors  in  per- 
ception. "When  the  bottom  lines  of  a  distant  object  are  covered, 
its  distance  and  shape  in  the  third  dimension  become  uncertain  to 
the  eye.  Mountains  that  tower  behind  each  other  seem  to  lie  in 
one  surface,  provided  the  presence  of  other  secondary  helps,  such 
as  atmospheric  j^erspective,  etc.,  is  excluded.  The  parts  of  un- 
shaded geometrical  figures  drawn  on  a  plane  where  the  course  of 
their  outlines  does  not  define  the  matter  to  us  as  fixed  in  one  way, 
may  often  receive  two  or  more  interpretations ;  they  may  thus 
actually  appear  as  subject  to  change  from  a  nearer  to  a  more  I'e- 
mote  place  in  space.     The  same  arrangement  of  lines  may  appear 

either  as  a  staircase  or  a 
portion  of  an  overhang- 
ing wall  (see  Fig.  102). 
The  same  angle  of  a  poly- 
gon may  be  made  to  seem 
either  the  nearest  or  the 
most  remote.  Indeed, 
the  whole  stereoscopy  of 
certain  figures  may  thus 
easily  be  reversed.  But 
if  the  course  of  the  limit- 
ing lines  of  an  object  for- 
bids moi'e  than  one  interpretation  of  the  relations  of  its  parts  in 
the  third  dimension  of  space,  then  the  object  must  be  seen  as  in- 
terpreted in  that  one  way.  Objects  of  known  size  and  shape  are 
seen  as  nearer  or  remote,  according  to  the  manner  in  which  the 
parts  cover  each  other  and  are  covered  by  each  other.  The  con- 
tour of  an  object,  then,  is  one  determining  factor  of  its  stereoscopic 
appearance  (see  Fig.  103). 

'  Comp.  Wundt,  Pliysiolog-.  Psycliologie,  ii.,  p.  145  f. ;  and  Helmholtz,  Phys- 
iolog.  Optik,  pp.  623  ff.  and  766  ff. 


/    / 

(5 

b 

^ 

0 

y^ 

a 

y^ 

a 

^ 

_/ 

Pig.  102  (From  Wundt). — a  can  be  made  to  apprar  either 
nearer  or  farther  off  than  6. 


i:NFLlTE]SrCE   OF   SECOISTDAEY   HELPS. 


445 


Mathematical  perspective,  or  the  size  of  the  angle  of  vision  which 
is  covered  by  near  and  far  objects  respectively,  is  one  of  the  most 
important  secondary  helps  of  stereoscopic  vision  and  vision  of  per- 
spective. In  this  way  objects  of  known  size  are  seen  as  placed  at 
a  distance  necessary  to  give  them  their  apparent  size.  The  street 
ajipears  narrower  and  more  distant,  the  houses  lower  and  more  re- 
mote, in  the  upper  part  of  its  visual  picture.  Parallel  lines,  like 
the  tracks  of  a  railway,  appear  to  converge  from  us  more  and  more 
toward  a  point  ;  the  same  thing  is  true  of  the  sides  of  the  table  or 
box  at  one  end  of  which  we  are  standing,  or  of  the  walls  of  the 


Fig.  103  (From  TVundt).— The  two  rings  A  and  B  may  be  stereoscopioally  combinprl  in  either  of 
the  following  ways— according  as  the  vertical  or  horizontal  contours  prevail. 

room.  For  although  the  perspective  of  visual  experience  is  very 
different  from  true  "  mathematical  perspective,"  the  latter  affords 
to  the  former  one  of  the  secondary  helps. 

More  distant  objects  are  also,  on  account  of  the  amount  of  atmos- 
phere through  which  the  rays  of  light  reflected  from  them  have  to 
pass,  more  dim  in  outline  and  of  changed  shades  of  color.  Such 
alterations  in  the  character  of  the  image  furnish  another  of  the 
secondary  helps  of  our  vision  of  perspective.  Accordingly,  things 
are  seen  nearer  in  a  clear  atmosphere,  more  distant  in  one  less 
clear.     This  is  sometimes  called  "aerial  perspective," 

The  size  and  direction  of  the  shadows  also  fui'nish  data  for  the 


446  BIXOCULAIl   FIELD    OF   SIGHT. 

perception  of  the  distance  and  shape  in  the  third  dimensions  of  vis- 
ual objects.  In  the  morning  and  evening  light,  when  all  shadows 
are  lengthened,  the  objects  of  the  landscape  appear  more  distant 
from  us  and  from  each  other.  The  direction  of  the  shadows  of 
different  objects  with  relation  to  each  other  and  to  the  source  from 
which  the  light  comes  is  also  an  aid  to  vision  of  perspective.  The 
arrangement  of  the  lights  and  shadows  is  by  far  the  most  impor- 
tant means  for  determining  the  relative  position  in  space  of  differ- 
ent parts  of  objects  like  intaglios  or  medallions.  A  change  of  the 
arrangement  of  the  lights  and  shadows  of  such  an  object,  so  as  to 
substitute  the  one  for  the  other  throughout,  converts  an  intaglio 
into  a  medallion  or  bas-relief,  and  vice  versa.  A  medallion,  placed 
near  a  window,  but  shielded  from  its  direct  light,  and  lighted  from 
the  other  side  by  reflection  from  a  mirror,  has  its  relief  reversed. 

§  23.  Other  secondary  helps  to  stereoscopic  vision  and  vision  of 
perspective  are  derived  from  experience  in  a  still  more  indirect 
way.  Within  certain  hmits  we  see  what  we  know  to  be  in  the 
field  of  vision  ;  but,  on  the  other  hand,  we  are  not  infrequently 
compelled  to  see  what  we  know  cannot  be  there.  The  account  of 
such  phenomena  depends  upon  laws  of  association  and  reproduc- 
tion, the  physical  basis  for  which  is  exceedingly  obscure.  Since 
the  ultimate  psycho-physical  processes  take  place  in  the  brain  ; 
and  since  the  central  processes  come  under  the  law  of  habit  and 
are  in  part  determined  by  the  tendencies  embedded,  as  it  were,  in 
the  structure  and  customary  functions  of  the  central  mechanism  ; 
the  influence  of  changes  in  the  peripheral  organs  of  vision,  the 
shape  and  clearness  of  the  retinal  image,  etc.,  cannot  always  deter- 
mine just  what  the  presentation  of  sight 
will  be.  Many  retinal  images  admit  of 
two  or  more  interpretations — which  in- 
terpretation will  be  chosen  depends 
upon  a  variety  of  circumstances  that 
perhaps  cannot  all  be  accurately  defined. 
The  few  lines  drawn  upon  the  black- 
board, or  employed  by  the  skilful  etch- 
er, cause  us  to  see  Avhat  is  not,  but 
rather  ougld  to  be,  in  the  image  formed 
Pio.  i04.-First  one,  thenThe  other  upou  the  retina.     Anyone  accustomed 

corner  of  the  figure  may  be  drawn    ^.^    gtudviuCf    the    effect    of    the    Colored 
forward,  partly  at  will.  J       o  •      ji_ 

points  and  outlines  which  appear  m  the 
image  seen  with  closed  eyes  by  the  retina's  own  light,  knows  how 
apparently  lawless  is  the  interpretation  given  to  this  image.  This 
is  especially  true  when  attention  is  somewhat  relaxed — as,  for  exam- 


INFLUENCE    OF   EXPERIENCE.  447 

pie,  on  sinking  into  re  very  or  sleep.  Much  of  the  "stuff"  out  of 
which  the  usual  phenomena  of  dreams  are  made,  may  be  suggested 
and  controlled  by  the  condition  of  the  "retinal  field."  In  all  these 
cases,  only  a  sharper  attention  and  more  objective  view  of  things  is 
needed  to  dispel  the  illusion  and  make  us  aware  how  scanty  is  the 
schema,  as  it  were,  out  of  which,  by  association  and  reproduction,  we 
have  constructed  our  presentations  of  sense.  Similar  experiences  not 
infrequently  occur  even  with  open  eyes  by  day,  in  the  dimly  lighted 
room,  or  in  the  obscurer  nooks  and  recesses  of  vision  on  the  street. 
In  this  way  numberless  ghosts  and  apparitions  have  been  most  per- 
spicuously seen.  The  face  of  a  friend  whom  we  know  to  be  thou- 
sands of  miles  distant  may  look  at  us  from  the  window  of  a  house  ; 
it  is  only  after  persistently  trying  to  interpret  the  appearance  in  ac- 
cordance with  our  knowledge  that  we  finally  succeed  in  resolving 
the  face  into  some  chance  combination  of  lights  and  shadows,  of 
window-sash,  curtain,  or  other  objects. 

§  24.  Phenomena  like  the  foregoing  recall  once  more  the  gen- 
eral office  of  experience  in  determining  the  existence  and  character 
of  particular  presentations  of  visual  sense.  We  have  seen  that  the 
strife  between  the  two  rival  theories  of  the  oi-igin  and  development 
of  sense-perception  concerns  the  relative  amount  of  what  is  to  be 
counted  "native,"  on  the  one  hand,  or  accredited  to  a  process  of 
"  learning  "  how  to  perceive  on  the  other  hand. 

The  analysis  of  the  mind's  data  or  motifs  has  made  it  apparent 
that  the  influence  of  experience  through  the  association  and  repro- 
duction of  its  past  forms  is  very  great  over  the  presentations  of 
sense.'  The  mind  sees,  not  simply  according  to  the  objective 
character  of  so-called  "  things,"  nor  siinply  according  to  the  retinal 
images  as  connected  with  sensations  of  motions,  but  also  accord- 
ing to  its  custom  in  seeing.  When,  therefore,  its  habits  are  broken 
up  for  the  time,  its  interpretation  of  the  sensations,  as  well  as  its 
synthesis  of  them  into  recognized  objects  of  sense,  is  liable  to  be 
disturbed.  Various  experiments  impress  this  truth  in  a  vivid  way. 
For  example,  let  one  regard,  with  one  eye,  the  reversed  picture  of 
a  landscape  or  the  photograph  of  a  friend  turned  upside  down 
after  covering  up  nearly  all  of  it  except  the  face.  The  effect  of  the 
pseudoscope,  or  optical  instrument,  which,  by  exchanging  the  two 
stereoscopic  pictures,  changes  convex  into  concave,  and  vice  versa, 
when  applied  to  a  complicated  scene  of  landscape,  streets,  etc.,  is 
very  bewildering.     The  data  with  which   the   mind  has  been  wont 

'  Comp.  the  chapter,  Der  Einfluss  der  Erfahrungsmotive  auf  die  Localisi- 
rung,  in  Hering's  Physiolog.  Optik,  Hermann's  Handb.  d.  Physiol.,  III.,  i. ,  pp 
564  fE. 


448  BINOCULAR   FIELD   OF   SIGHT. 

to  deal  may  all  be  given,  and  the  sensations  localized  according  to 
the  laws  of  stereoscopic  vision,  but  the  relation  of  the  parts  is  in- 
exj)licable  out  of  any  previous  experience.  Similar  effects  are  pro- 
duced by  the  telestereoscope,^  or  optical  instrument  which  enables 
us  to  see  a  larger  portion  of  a  distant  object  than  is  possible  with 
two  ordinary  eyes,  after  the  fashion  of  a  pair  of  optical  organs  in 
the  sides  of  a  gigantic  head.  Individual  peculiarities  of  localizing, 
such  as  are  acquired  by  the  practice  of  some  trade  or  art,  are  also 
accounted  for  under  the  princqile  of  irijluence  from  experience  over 
those  elements  of  reproduction  that  determine  what  object  of  sense 
shall  be  constructed  out  of  the  various  sensational  data  at  command. 
Indeed,  all  our  estimates  of  visual  size,  shape,  and  distance,  as  well 
as  our  "  errors  of  sense,"  can  be  understood  only  in  the  light  of 
this  same  general  principle. 

§  25.  Not  only  what  we  know,  but  what  we  choose,  has  an  influ- 
ence— often  a  determining  one — upon  what  we  see.  This  is  true, 
not  simply  because  we  can  at  will,  within  certain  limits,  decide  the 
area  of  the  field  of  vision  over  which  the  point  of  regard  shall  move, 
as  well  as  the  parts  of  this  area  upon  which  it  shall  be  fixated,  but 
also  because  we  can  regulate  the  amount  of  attention  which  shall 
be  given  to  visual  impressions  and  the  manner  of  the  distribution 
of  attention  over  the  various  parts  of  these  impressions.  Further- 
more, it  often  lies  with  us  to  say  how  we  will  interpret  the  data, 
and  so  see  the  complex  product  resulting  from  the  act  of  mental 
synthesis.  This  is  especially  true  of  geometrical  figures  in  outline, 
as  in  the  cases  already  referred  to  under  another  head  (§  22). 

§  26.  With  the  use  of  the  foregoing  data,  and  under  the  guidance 
of  past  experience,  we  judge  of  the  spatial  extension  and  relations 
of  lines,  angles,  and  solid  bodies,  of  their  shape,  size,  distance,  and 
relative  situation.  The  position  of  lines  and  angles  affects  our  es- 
timate of  their  magnitude  ;  under  this  principle  many  errors  of  sense 
originate.  Distance  and  size  are,  of  course,  so  related  that  they  vary 
inversely,  and  when  one  is  known  the  other  is  immediately  or  readily 
judged  on  the  basis  of  such  knowledge.  But  the  size  of  the  visual 
object  is  measured  by  the  magnitude  of  the  visor  angle  covered  by 
its  image,  or  the  relative  extent  of  the  retinal  surface  simultaneously 
excited  by  the  rays  of  light  reflected  from  the  object.  This  is  called 
its  "  apparent  magnitude."  The  real  magnitude  of  any  object  is  its 
size  as  related  to  certain  fixed  standards  of  measurement  formed  on 
the  basis  of  generalizations  from  the  use  of  both  eye  and  hand.  Dis- 
tance, apparent  magnitude,  and  real  magnitude,  are  therefore  con- 

'  See  Helmholtz,  Pliysiolog.  Optik,  p.  646  f.,  for  an  account  of  these  two  in- 
struments. 


INFLUENCE   OF   INTENSITY.  449 

nected  as  three  factors  of  one  problem  proposed  by  each  presentation 
of  sight.  Given  the  apparent  magnitude  and  the  real  magnitvide  of 
an  object,  we  judge  of  the  distance  according  to  our  experience  of 
how  large  an  object  of  such  size  appears  at  an  assumed  distance. 
The  remote  spot  on  which  a  human  figure  is  standing  seems  nearer 
or  farther  away  according  as  we  know  the  figure  to  be  that  of  a 
man  or  that  of  a  boy.  Distance  and  apparent  magnitude  being 
given,  the  real  magnitude  of  the  object  is  judged  as  that  which  it 
would  need  to  have  in  order  to  appear  so  large  at  the  given  dis- 
tance. When  one  of  the  two  necessary  data  is  lacking,  no  judg- 
ment can  be  formed  except  upon  the  basis  of  other  secondary  helps, 
such  as  aerial  perspective,  etc.  Thus,  no  common  standard  for  es- 
timating the  distance  of  the  sun  or  moon  being  given,  their  size  ap- 
pears different  according  to  the  place  whei-e  different  observers  are 
inclined  to  locate  them,  or  according  to  the  standard  of  comparison 
made  necessary  for  the  time  by  their  position.  These  bodies  ordi- 
narily appear  to  some  persons  no  larger  than  a  saucer,  to  others 
larger  than  a  large  cart-wheel.  "When  the  sun  sets  behind  a  tree, 
the  size  of  the  spreading  of  whose  branches  is  fairly  well  known,  it 
may  be  enormously  magnified  by  being  seen  to  fill  its  branches  en- 
tirely. 

§  27.  When  the  eye  is  in  motion,  as  in  all  ordinary  vision  of  ob- 
jects not  very  minute  and  very  near,  the  number,  duration,  and  in- 
tensity of  the  spatial  series  of  sensations  called  forth  by  the  motion 
determine  our  estimate  of  the  outline-form,  magnitude,  and  dis- 
tance of  the  objects.'  Every  spatial  series  of  sensations  contrib- 
utes the  lai'ger  magnitude  to  the  object  the  greater  the  number  of 
members  which  enter  into  the  series.  For  this  reason  the  same 
extension  of  a  line  or  surface  when  broken  up  into  parts  by  inter- 
secting lines  appears  larger  than  when  perceived  as  an  uninter- 
rupted whole.  The  repetition  of  similar  figures  in  architecture, 
upon  walls,  columns,  etc.,  takes  advantage  of  this  effect. 

The  intensity  of  the  sensations  of  a  spatial  series,  and  of  the  act 
of  attention  necessary  to  comprehend  them  in  one  whole  as  a  pres- 
entation of  sense,  also  has  an  influence  on  the  size  of  the  object. 
When  the  movements  of  the  eyes  are  made  with  lamed  or  tired 
muscles,  the  size  of  the  thing  perceived  by  them  is  increased. 
When  the  function  of  one  of  the  muscles  (for  example,  the  rectus 
externus)  is  impaired,  so  that  the  circuit  of  the  eye  in  a  given  direc- 
tion is  shortened,  objects  lying  at  any  position  in  the  field  of  vi- 
sion, as  seen  by  the  eye  moving  in  the  shortened  circuit,  are  located 
where  they  would  have  been  if  the  same  intensity  of  muscular  sen- 

'  Comp.  Volkmann  von  Volkmar,  Lehrb.  d.  Psychologie,  1885,  II.,  pp.  99  fif. 
29 


450  BINOCULAR  FIELD   OF   SIGHT. 

sation  had  been  necessary  to  bring  them  to  this  position  with  a 
normal  function  of  the  muscles.  A  patient  with  paralysis  which 
prevents  turniug  the  eye  more  than  20""  will  locate  an  object 
actually  lying  only  20°  from  the  median  plane  much  farther  to 
one  side.  Such  a  patient  will  reach  beyond  when  he  tries  to  grasp 
the  visual  object.  The  increased  size  which  is  given  to  objects 
that  are  parti-colored  or  mottled,  and  so  have  an  interrupted  sur- 
face and  furnish  greater  difficulty  to  perception  of  them  as  wholes, 
may  be  due  to  both  the  foregoing  causes.  Volkmann  von  Volk- 
mar '  calls  attention  to  the  fact  that  both  monotony  and  variety 
may,  under  the  working  of  these  principles,  be  productive  of  the 
same  effect  in  magnifying  the  size  of  an  object.  For  the  size  of 
any  visual  surface  is  usually  estimated  by  the  application  of  some 
standard  of  measurement  selected  from  the  field  of  vision.  The 
frequent  repetition  of  this  standard  creates  the  impression  of  vast- 
ness  ;  and  the  absence  of  any  standard  to  apply,  or  a  vague,  unsuc- 
cessful effort  to  find  a  standard,  may  produce  the  same  impression. 
Monotonous  areas  of  unbroken  snow,  and  stretches  of  streets 
crowded  with  forms  of  men  and  animals,  both  seem  of  great  ex- 
tent. 

The  amount  of  time  through  which  the  spatial  series  of  sensa- 
tions endure  has  also  an  influence  on  the  magnitude  of  the  objects 
perceived  through  those  sensations.  It  is  as  enduring  in  time  that 
the  changing  qualities  and  quantities  of  sensation  which  belong- 
to  the  perception  of  any  complex  object  are  expressed.  The  length 
of  the  time-course,  as  well  as  the  degree  of  the  intensity  of  the  spa- 
tial series  of  sensations,  may  be  interpreted  as  extensive  magnitude 
of  the  perceived  object. 

8  28.  The  laws  which  control  our  estimates  of  visual  magnitudes 
are  psychological,  and  apply  to  all  the  action  of  the  mind  in  con- 
structing its  sense-data  into  the  presentations  of  sense.  Yet  more 
elaborate  mental  activities,  such  as  take  place  when  the  distance, 
size,  and  contour  of  visual  objects  are  deliberately  estimated  and 
expressed  in  terms  of  an  accepted  standard,  of  course  imply  more 
of  dependence  upon  skill  acquired  through  experience. 

The  degree  of  fineness  with  which  differences  of  distance  and 
maernitude  can  be  seen,  under  the  most  favorable  circumstances,  is 
limited  by  the  least  observable  differences  in  the  members  of  the 
spatial  series  of  sensations  which  compose  the  visual  objects.  Of 
such  series,  those  most  capable  of  exceedingly  fine  differentiation 
are  the  local  retinal  signs  and  the  muscular  sensations  accompany- 
ing convergence  of  the  eyes  for  near  distances.  It  is  difficult 
'  Lehrb.  d.  Psycliologie,  II.,  p.  101  f. 


MEASURING  POWER   OF   THE   EYE.  451 

to  assign  the  exact  proportion  of  help  which  these  two  series  ren- 
der in  making  the  finest  possible  distinctions  of  visual  magnitude. 
Heriug '  denies  that  any  help  is  obtained  from  muscular  sensations, 
or  "feelings  of  innervation,"  in  comparing  the  size  of  two  miniite 
objects  near  bj",  and  assigns  all  the  work  of  furnishing  such  data  to 
the  "spatial  sense  of  the  retina."  Lotze,"  who  admitted  the  as- 
sistance of  muscular  sensations,  nevertheless  held  that  the  fineness 
of  the  distinctions  possible  among  them  is  not  sufficient  to  support 
our  ordinary-  judgments  of  the  size,  distance,  and  direction  of  ob- 
jects. Wuudt '  and  others  claim  that  it  is  by  gradations  in  the  so- 
called  "  feelings  of  innervation  "  alone  that  we  make  the  most  accu- 
rate of  these  estimates  ;  they  deny  that  any  "  spatial  sense "  (in 
Hering's  meaning  of  the  words)  belongs  to  the  retina.  The  evi- 
dence seems  to  favor  the  view  that  both  the  muscular  sensations  and 
the  local  retinal  signs  furnish  data  for  all  nice  discrimination  of 
visual  extension. 

The  particular  degree  of  accuracy  with  which  minute  differences 
in  the  distance  and  magnitude  of  visual  objects  can  be  perceived 
varies  gi-eatly,  according  to  different  positions  of  the  eyes  and  the 
object,  the  amount  of  light,  practice,  etc. — and  all  these,  as  con- 
nected with  individual  peculiarities  of  structure  and  previous  func- 
tion of  the  organs  of  sense.  That  such  estimates  fall  to  some  extent 
under  Weber's  law — in  other  words,  that  the  least  observable  dif- 
ference in  the  length  of  visual  lines  and  surfaces  is  relative  and 
not  absolute — has  already  been  shown  (Chap.  V.,  §  18).  Chodin 
found  the  relative  value  of  the  least  observable  difference,  with  a 
variation  of  the  absolute  vertical  distance  from  2.5  to  160  mm.,  to 
be  as  follows  when  the  lines  lie  in  the  same  direction : 
Absolute  distance. .        2.5  5  10  20  40  80         160  mm. 

Fraction  of  observ-  (    j       i_  _i       i     i      _i     i_    j.     i_      i     i       i     i       j. 
able  difference,  f  '^     ^^   ^y—'ji  37"— 45'  '5i~  of  44     i6  iS~'j2   4a~3u 

The  fineness  of  ocular  judgment  is  greater  for  horizontal  dis- 
tances. 

The  measuring  power  of  the  eye  is  much  less  accurate  when  the 
distances  compared  lie  in  different  directions.  In  particular,  points 
lying  at  a  vertical  distance  of  20  mm.  are  estimated  as  equally  far 
away  with  those  lying  at  a  horizontal  distance  of  25  mm.''  Most 
estimates  of  direction  and  distance  are  comparatively  inaccurate 
when  only  one  eye  is  used.     A  vertical  line  drawn  at  right  angles  to 

'  Hermann's  Handb.  d.  Physiol.,  III.,  1  ,  p.  533  f. 

^  Medicin.  Psychologie,  3b4  f. 

^Physiolog.  Psychologie,  ii.,  pp.  85  fif. ;  comp.  1.,  pp.  875  S, 

-  So  "Wundt  found,  Physiolog.  Psychologie,  ii, ,  p.  96. 


452  BiJsrocuLAE  field  of  sight. 

a  horizontal  appears  bent  to  monocular  vision  ;  its  apparent  inclina- 
tion is  variable,  and  was  found  by  Bonders  '  to  vary  between  1°  and 
3°  of  the  angle  within  a  short  time. 

Helmholtz  '^  experimented  to  determine  the  accuracy  of  the  bi- 
nocular perception  of  depth  by  trying  how  small  a  deviation  from  a 
perfectly  straight  line  could  be  detected  in  a  wire  bent  atone  point 
so  that  its  two  halves  formed  an  extremely  obtuse  angle,  when  the 
wire  was  looked  at  both  in  and  out  of  the  horoiDteric  line  ;  he  also 
employed  for  the  same  purpose  three  nails,  the  heads  of  which  could 
be  very  slightly  displaced  from  a  straight  line.  Under  the  most 
favorable  circumstances,  he  found  that  a  displacement  of  a  nail  by 
a  change  of  its  distance  corresponding  to  60|-  seconds  of  the  angle 
of  vision,  or  0.0044  mm.  variation  in  the  position  of  the  retinal 
image,  could  be  detected.  The  latter  distance  corresponds  so  well 
to  the  calculated  size  of  the  retinal  elements  (see  p.  327)  as  to  form 
an  argument  in  favor  of  the  theory  that  estimates  of  size  and  dis- 
tance are  dependent  upon  the  local  signs  attached  to  the  excitation 
of  these  elements. 

But,  on  the  other  hand,  it  is  claimed  that  Weber  ^  showed  the 
muscular  sense  of  the  eye  to  be'  one  of  the  finest  of  micrometric 
apparatuses,  since  a  distinct  muscular  sensation  is  attached  to  a 
displacement  of  the  most  sensitive  spot  of  the  retina  of  not  more 
than  j^2j  of  a  Parisian  line.  By  experimenting  with  a  black  thread 
stretched  over  against  a  white  Avail  and  moved  in  the  median  jDlane 
toward  and  from  both  eyes,  which  looked  at  it  through  a  horizon- 
tal slit  in  an  upright  board,  it  was  found  j^ossible  to  detect  changes 
in  distance  of  3.5  ctm.  at  an  absolute  distance  of  180  ctm.,  and 
changes  of  1  ctm.  at  an  absolute  distance  of  60  ctm/ 

§  29.  The  data  or  motifs  already  described  are  the  foundation, 
also,  of  our  perceptions  of  motion,  and  of  our  estimates  of  its  di- 
rection, speed,  and  extent.  It  need  scarcely  be  said  that  all  such 
perceptions  and  estimates  are  relative  ;  they  imply  the  existence  of 
some  point  which  may  be  regarded  as  fixed,  and  the  application  of 
a  standard  of  measurement.  For  j)erceptions  of  motion  by  the  eye, 
the  point  of  regard  when  the  organ  is  in  the  primary  position 
furnishes  the  means  of  orientating  ourselves  and  of  placing  the  dif- 
ferent things  of  vision  in  their  right  relations  to  us  and  to  each 
other.    Sujopose  the  body  and  head  to  be  erect,  and  the  eyes  motion- 

1  Archiv  f.  Oiihthalmologie,  XXI.,  iii.,  p.  100  f. 

2  See  Pliysiolog.  Optik,  p.  644  f. 

^  In  the  Ber.  d.  sachs  Gesells. ,  etc. ,  for  1852,  p.  130;  cited  by  Volkmann 
von  Volkmar,  Lelirb.  d.  Psychologie.,  II.,  p.  56. 

^  See  Wuudt,  Physiolog.  Psychologie,  ii.,  94  f.,  and  the  reference  there. 


THE   PERCEPTIOlSr    OF   MOTION.  453 

less  and  looking  into  the  distance  with  the  Hnes  of  vision  parallel ; 
the  perception  of  motion  may  then  arise  in  either  one  of  two  ways. 
Of  these,  by  far  the  most  frequent  is  the  change  of  relative  position 
of  an  object  in  the  field  of  vision  which  is  occasioned  by  its  move- 
ment. What  is  necessary,  however,  is  simply  the  successive  stimu- 
lation of  continuous  points  or  areas  of  the  retina  with  images  that 
are  sufficiently  similar  to  be  perceived  as  one  object.  The  percep- 
tion of  motion  may  also  be  produced  by  the  successive  stimulation 
of  the  same  points  or  areas  of  the  retina  with  images  that  are  too 
dissimilar  to  be  regarded  as  one  object.  One  may  thus  see  motion 
when  neither  the  eyes  nor  any  external  objects  are  really  moved. 
It  is  in  the  latter  way  that  the  colored  points  of  the  images  formed 
by  the  retina's  own  light,  when  the  eyes  are  closed  and  motionless, 
seem  to  be  in  constant  motion. 

The  direction  and  amount  of  motion  perceived  with  the  ej-es  is 
measured  off  upon  the  entire  field  of  vision  in  accordance  with  pre- 
vious experience  and  by  means  of  the  data  already  described.  With 
the  eyes  at  rest,  the  retinal  local  signs,  or  space-values  belonging 
to  the  retinal  elements,  furnish  the  only  primary  data  ;  secondary 
helps,  and  associated  ideas  of  muscular  sensations  which  have  been 
by  experience  found  necessar'y  to  follow  objects  in  motion,  complete 
the  perception. 

It  is  assumed,  in  cases  like  the  foregoing,  that  no  sensations  in- 
dicating  motion  of  either  the  organ  of  vision,  or  the  head,  or  the 
whole  body,  complicate  the  pi'oblem.  But  ordinary  perceptions  of 
motion  are  gained  with  the  eyes  in  motion  out  of  the  primary 
position.  When  the  eye  and  the  object  both  move  in  such  a  way 
that  the  point  of  regard  remains  fixed  on  the  object,  our  percep- 
tions of  motion,  and  estimates  of  its  direction  and  magnitude  are 
dependent  upon  muscular  and  tactual  sensations  occasioned  by  the 
eye's  changes  of  position.  We  know  from  experience  what  kinds 
and  intensities  of  sensations  are  produced  by  keeping  the  point  of 
regard  fixed  on  an  object  which  is  moving  at  about  a  given  rate  in 
a  given  direction.  If  any  of  the  links  ordinarily  belonging  to  this 
chain  of  conscious  experiences  drop  out,  our  measuring  instru- 
ment fails  us  either  partially  or  completely.  The  head,  too,  is  in- 
variably turned  when  we  are  watching  an  object  that  is  moving  in 
any  direction  other  than  straight  forward  or  away  from  us  along  the 
line  of  regard.  The  sensations  originating  in  the  action  of  the 
muscles  and  skin  of  the  head  and  neck  thus  enter  into  our  compu- 
tation ;  they  must  have  such  a  value  in  consciousness  as  to  inform 
us  about  how  far  the  head  has  gone  from  the  position  with  which 
it  started,  in    order  to  fixate  the  moving   object.     According  to 


454  BINOCULAR   FIELD   OF   SIGHT. 

Eelmholtz/  the  ordinary  movements  of  the  head  in  vision  follo^v 
the  same  principle  as  that  followed  by  the  eyes  in  movement ;  that 
is  to  saj',  the  head  turns  fi'om  its  primary  position  on  an  axis  that 
is  approximately  parallel  to  the  axis  of  the  simultaneous  rotation 
of  the  eyes.  But  Hering  "  asserts  that  a  difference  between  the  laws 
of  the  motion  of  head  and  eyes  is  of  essential  significance  for  our 
perception  of  space.  However  this  may  be,  it  is  certain  that  the 
position  and  motion  of  the  head,  as  known  by  its  muscular  and 
tactual  sensations,  must  be  taken  account  of  in  all  ordinary  visual 
perception  of  motion.  The  same  thing  is  true  of  the  j)osition  and 
motion  of  the  entire  body.  Many  of  our  errors  of  sense,  or  false 
perceptions  of  motion — its  existence,  direction,  rate,  and  amount — 
are  dependent  upon  the  principles  of  judgment  governing  such 
data  of  sensations.  AYe  are  peculiarly  liable  to  error  in  all  cases 
where  the  motions  of  our  own  bodily  organs  are  passive  ;  in  such 
cases  we  do  not  have  the  ordinary  motifs,  or  data,  at  our  command. 
Objects  are  perceived  at  rest,  either  when,  our  organs  of  vision 
being  themselves  at  rest,  the  images  of  the  objects  do  not  change 
their  position  in  the  field  of  vision,  or  when  sensations  of  motion 
occasioned  by  moving  these  organs  are  such  and  so  great  as  we 
know  by  experience  correspond  to  (or  compensate  for)  the  changes 
in  the  position  of  their  images  which  are  occasioned  by  their  actu- 
ally remaining  at  rest.  But  whenever  we  look  with  moving  eyes 
upon  a  number  of  objects  arranged  in  fixed  position  with  relation  to 
each  other,  a  conflict  between  two  sets  of  data  i-eally  takes  place. 
The  result  with  respect  to  our  perceptions  of  motion  may  depend 
upon  which  of  the  two  is  chiefly  effective  in  arresting  attention. 
When  the  eyes  are  brought  from  the  parallel  position,  which  they 
assume  in  vision  of  remote  objects,  to  convergence  upon  some  near 
object,  the  two  fields  of  view  belonging  to  the  two  eyes  rotate  in 
opposite  directions,  while  the  middle  visual  line  maintains  its  posi- 
tion in  the  median  plane.  ^  Ordinarily  we  do  not  perceive  this 
rotary  motion  of  the  two  fields  of  vision,  but  consider  the  field  as 
one  and  stationary  and  ourselves  as  changing  our  point  of  regard  in 
it.  By  attention,  however,  we  may  see  that  the  external  objects, 
although  they  really  continue  at  rest,  appear  to  move  as  the  rela- 
tions of  their  double  images  are  changed.  So,  also,  when  the  eye 
or  head  or  body  turns  in  either  direction,  in  order  that  a  new  ob- 
ject may  be  brought  under  regard,  it  is  possible  either  to  perceive 
or -not  to  perceive  the  entire  field  of  objects  sweeping  by  ;  which 

J  Physiolog.  Optik.  p.  486. 

■^  In  Hermann's  Handb.  d.  Physiol.,  III.,  i.,  p.  495. 

^  See  Le  Coute,  Siglit,  p.  229. 


VISIOlSr   AS    INTEEPRETATIOlSr.  455 

of  the  two  happens  depends  upon  the  dii'ection  in  which  attention 
is  drawn.  When  strictly  attending  to  the  phenomena,  we  cannot 
well  fail  to  regard  everything  as  moving  in  the  opposite  direc- 
tion from  that  in  which  we  know  the  organ  of  vision  to  be  turn- 
ing. 

§  30.  The  principles  already  laid  down  also  suffice  to  explain 
most  of  the  ordinary  "  errors  of  sense,"  as  well  as  certain  extraor- 
dinary experiences  of  a  somewhat  different  kind.  The  right  to 
speak  of  errors  of  sense  has  been  questioned.  It  has  been  claimed 
that  such  errors  belong  rather  to  judgment,  and  that  sense  pure 
and  simple  cannot  err.  The  claim  is  based  upon  a  misunderstand- 
ing of  the  nature  of  perception.  A  very  obvious  difference  exists, 
indeed,  between  a  mistaken  estimate  of  the  distance  of  a  mountain 
through  extraordinary  clearness  of  atmosphere  and  the  seeing  of  a 
square  of  white  paper  as  green  on  a  red  ground,  or  as  yellow 
on  a  blue  ground.  Bat  the  latter  is  surely  an  "  en*or  of  sense,"  or 
sensation,  in  as  pure  form  as  such  error  is  conceivable.  That  sense 
cannot  err  is  true  only  in  case  we  speak  of  unlocalized  and  unpro- 
jected  sensation,  regarded  as  not  predicating  anything  beyond  itself. 
In  all  presentations  of  sense  a  certain  psychological  judgment  is 
involved  ;  for  all  such  presentations  imply  association  of  impres- 
sions discriminated  as  similar  or  dissimilar,  and  a  mental  synthesis 
which  is  dependent  upon  attention  and  the  interpretation  of  certain 
motifs  or  data  according  to  past  experiences.  Clear  vision  is  always 
mental  interpretation. 

The  attempt  to  assign  the  relative  amount  of  blame  to  sense  and 
to  intellect,  in  cases  where  our  presentations  of  sense  do  not  rep- 
I'esent  objective  relations  of  things,  assumes  an  ability  to  make  dis- 
tinctions which  we  do  not  possess.  Moreover,  the  distinction,  when 
made  as  the  objection  would  have  it,  will  not  hold.  Innumerable 
experiences  contradict  the  statement  that  immediate  sense-percep- 
tion cannot  err.  When  one  sees  (with  no  power  to  see  otherwise) 
a  gigantic  human  form  through  the  fog,  or  projected  against  the 
scenery  of  a  stage,  and  yet  judges  that  this  form  is  only  of  usual 
size,  the  error  is  not  one  of  judgment,  but  just  the  reverse.  Errors 
of  sense  are  only  special  instances  where  the  mind  makes  its  syn- 
thesis unfortunately,  as  it  were,  out  of  incomplete  data,  instantane- 
ously and  inevitably  interpreting  them  in  accordance  with  the  laws 
which  have  regulated  all  its  experience.  As  Lotze  has  remarked, 
"  The  whole  of  our  apprehension  of  the  world  by  the  senses  is 
one  great  and  prolonged  deception."  Objects  of  sense  are  in  no 
case  exact  copies  of  ready-made  things  which  exist  extra-mentally 
just  as  they  are  afterward  perceived,  and  which  get  themselves 


456  EKEORS   OF   VISUAL   PERCEPTION. 

copied  off  in  the  mind  by  making  so-called  impressions  upon  it ; 
they  are  mental  constructions.  In  the  special  case  of  sight  we  have 
seen  that,  in  every  particular — in  its  elements,  its  mode  of  con- 
struction, its  laws  of  change — the  field  of  vision  is  a  subjective  af- 
fair. The  case  is  in  no  respect  essentially  different,  whether  our 
presentations  of  sense  are  so-called  errors  or  true  images  of  things. 
In  both  cases  the  same  data  and  laws  of  the  use  of  these  data  main- 
tain themselves.  Errors  of  sense,  however,  are  distinguished  from 
hallucinations,  because  the  former  result  from  the  activity  of  an 
organism  which  is  normal  in  structure  and  function,  while  the  lat- 
ter do  not. 

§  31.  The  errors  of  visual  perception  are  almost  innumerable  ; 
they  may  be  classified  in  part,  however,  according  as  they  fall  under 
some  one  or  other  of  the  before-mentioned  princij^les.  Such  errors 
may  be  called  "  normal,"  because  they  are  committed  in  accordance 
with  principles  which  regulate  the  ordinary  activity  of  the  mind  in 
making  its  synthesis  by  the  help  of  the  sense-data  or  motifs  fur- 
nished to  it  through  the  excitement  of  the  organism.  Deceptions 
of  this  class  really  result,  then,  from  the  fidelity  of  both  mind  and 
nervous  system.  Certain  errors  of  sense,  for  example,  are  special 
examples  of  the  working  of  the  laws  which  regulate  the  correspond- 
ence of  the  two  images  in  binocular  vision.  Thus,  near  objects 
erroneously  appear  double  when  the  eye  is  adjusted  for  distant 
vision,  distant  objects  when  it  is  adjusted  for  near  vision  ;  solid 
things  are  seen  through  other  solid  things  ;  relations  in  space  in 
general  are  perceived  different  from  the  reality  ;  and  all  according 
to  the  law  of  the  correspondence  and  non-correspondence  of  the 
two  retinal  images.  Accordingly,  the  inquiry,  Why  is  vision  single 
when  it  is  performed  with  two  eyes  ?  can  demand  and  receive  only 
one  answer.  A  chief  condition  of  the  single  vision  of  solid  objects 
is  that  they  shall  he  seen  with  two  eyes.  Whether  anything  what- 
ever is  seen  as  two  or  one  does  not  depend,  primarily,  upon  its 
really  being  either  two  or  one,  or  upon  the  existence  of  one  or  two 
retinal  images  of  it  (as  though  such  images  were  directly  perceived) ; 
it  rather  depends  upon  tlie  appropriate  data  of  sensations  being 
furnished  to  the  mind  for  completing  its  mental  synthesis  of  the 
object.  The  two  eyes  being  simultaneously  affected  in  a  certain 
way,  these  data  are  supplied.  What  is  one  is  seen  as  one,  and 
what  is  two  is  seen  as  one,  and  what  is  one  is  seen  as  two — all  in 
essentially  the  same  way. 

A  still  larger  class  of  errors  of  the  visual  sense  falls  under  the 
laws  which  regulate  the  smallest  observable  differences  in  the 
muscular  sensations  as  related  to  the  mathematical  perspective  of 


COMEAEISON   OF   MAGNITUDES. 


457 


lines,  angles,  and  surfaces/     Keference  has  already  been  made  to 

the  working  of  this  principle  in  our  ordinary  perceptions  of  the 

visual  magnitude,  contour,  and  distance  of  objects. 

Vertical  distances  are  regularly  perceived  as  larger     '      fiTTob       ' 

than  equally  large  horizontal  distances.    On  trying 

to  draw  a  cross  with  limbs  of  equal 

i  1  1  1  1 J  1  I  1  ]  I  length  one  is  apt  to  get  the  vertical 

dimension  too  small ;  exact  squares 
are  likely  to  appear  higher  than  their 


Fig.  106. 


breadth.  When  comparing  magnitudes  in 
the  upper  part  of  the  field  of  vision  with 
those  in  its  lower  part,  one  is  likely  to  over- 
estimate the  former.  The  upper  and  lower 
half  of  a  letter  "  S  "  or  a  figure  "  8  "  appear 
of  nearly  the  same  size  ;  but  when  they  are 
inverted  ("  g  "  and  "  g  ")  the  difference  in  the 
size  of  the  two  halves  becomes  magnified. 


Under  the  same  prin- 


ciple— in  part  at  least — may  those  errors  be  brought  which  are 


Fig.  108. 

determined  by  the  way  in  which  the  field  of  vision  is  filled  up.  If 
"the  horizontal  distance  between  two  points  be  exactly  half  filled 
with  a  line,  this  line  will  ap-      a\ 

pear  longer  than  the  remain-         \    | — .  \ 

ing  empty  space.     A  square  \  \ 

intersected  by  parallel  hori- 
zontal lines  appears  elongat- 
ed upward,  but  one  intersect- 
ed by  parallel  vertical  lines 
appears  elongated  sidewaj'S. 
If  one  of  the  two  right  angles 
formed  by  drawing  a  vertical 
perpendicular  to  a  horizontal 
line  be  filled  with  several  lines  diverging  from  the  point  of  the  an- 

'  Comp.  Wundt's  discussion  of  such  cases,  Physiolog.  Psycliologie,  II.,  pp 
92  ff. 


Fig.  109. 


\ 


LiU^ 


458 


ERRORS   OF   VISUAL   PERCEPTIOIST. 


gle,  the  angle  thus  filled  will  appear  the  larger  and  the  perpendic- 
ular will  seem  bent.  For  essentially  the  same  reason,  when  two 
unequal  angles  together  make  180°,  the  obtuse  angle  appears  rela- 


FlCr.    111. 


Fig.  112. 


tively  too  small,  and  the  acute  angle  relatively  too  large.  Many 
surprising  errors  of  sense  result  from  the  varied  applications  of  this 
principle.     (See  the  Figs,  on  p.  457  f.) 


THE    ILLUSION'S    OF    AET. 


459 


Fig.  113. 


§  32.  The  influence  of  experience,  which  often  corrects  what 
would  otherwise  be  an  instinctive  interpretation  of  the  data  fur- 
nished to  the  mind,  is  at 
other  times  the  cause  of 
errors.  If  the  data  will  at 
all  permit  it,  we  incline  to 
perceive  any  object  as  we 
know  that  similar  objects 
are  usually  perceived.  Such 
errors  of  sense  as  result 
from  the  vision  of  distant 
objects  through  secondary 
helps  are  too  well  known 
and  frequently  remarked 
upon  to  require  extended 
treatment.  All  the  pleasant 
illusions  of  art — in  archi- 
tecture, drawing,  and  paint- 
ing— are  obliged  constantly 

to  take  them  into  account.  The  very  relations  of  light  and  shade, 
the  conjunction,  separation,  and  covering  of  lines  and  surfaces,  upon 
which  reliance  is  ordinarily  placed  for  perception  of  fact,  may  be 
employed  by  either  nature  or  art  to  compel  us  to  perceive  what  is 
contrary  to  fact.  Painting  is  successful  according  to  the  skill  it 
displays  in  furnishing  to  the  eye  its  customary  data  so  as  to  entice 
it  to  regard  things  as  other  than  they  really  are.  That  its  success 
is  so  good  need  not  siu'prise  us,  when  we  remember  that  the  mind 
has  never  anything  more  than  these  same  data  out  of  which  to 
construct  its  objects  of  sense  and  to  make  its  various  judgments 
concerning  them.  The  man}'  errors  in  our  perceptions  of  motion 
may,  for  the  most  part,  be  explained  in  the  same  way.  It  matters 
not  whether  the  data  for  such  perceptions  are  furnished  by  actual 
changes  in  the  relative  position  of  things  in  external  space,  or 
whether  the  same  sensations  arise  through  changes  confined  to  the 
oi'gans  of  sense.  Past  experience  has  great  influence  in  all  this 
domain.  We  incHne  for  this  reason,  when  two  objects  are  chang- 
ing their  relative  jDosition,  to  perceive  the  smaller  of  them  as  in 
motion  ;  we  also  over-estimate  the  speed  of  small  bodies  in  motion, 
and  under-estimate  that  of  large  bodies. 

§  33.  Some  errors  of  visual  perception  differ  from  the  foregoing 
in  that  their  explanation  seems  to  be  due  to  cerebral  activity  under 
other  laws  as  yet  unknown  to  us.  We  have  alread}'  seen  (Chap. 
IV.,  §  IJ:)  that  the  phenomena  of  contrast  of  colors  must  be  referred 


460  ERRORS   OF   VISUAL   PERCEPTION". 

to  certain  inexplicable  activities  of  the  central  organs  as  related  to 
our  sensations  or  states  of  consciousness.  The  same  thing  is  ap- 
parently true  of  those  errors  of  sense  which  occur  in  connection 
with  the  strife  and  prevalence  of  contours,  and  the  binocular  mixing 
and  contrast  of  colors.  If  a  well-defined  image  of  some  contour, 
such  as  a  sharp-marked  limit  between  two  differently  colored  sur- 
faces, be  formed  on  one  retina,  and  on  the  corresponding  points  of 
the  other  the  image  of  a  uniform-colored  background,  then  only  the 
former  will  be  visible.  This  is  called  the  "  prevalence  of  contours." 
But  if  the  contours  of  the  images  of  two  differently  colored  objects 
run  on  the  retina  so  as  to  cross  only  in  one  place,  then  sometimes 
one  color  and  sometimes  the  other  will  prevail  and  get  itself  per- 
ceived at  that  j)lace.  This  is  called  "the  strife  of  contours."  If 
two  squares  of  red  paper  and  two  of  blue,  all  of  equal  size  and  bright- 
ness and  without  any  distinguishing  marks,  be  laid  side  by  side  at 
equal  distances,  and  their  images  then  combined,  the  color  of  the 
middle  one  of  the  binocular  images  will  at  first  be  sometimes  red- 
der and  sometimes  bluer  than  that  of  the  two  side  images,  but  in 
no  case  exactly  like  either  of  them.  By  steady  looking  it  is  said  to 
be  j)ossible  to  mix  the  colors  of  the  two  objects  in  a  binocular 
image  which  is  reddish  blue  (or  violet).'  This  is  called  "the  bi- 
nocular mixing  of  colors."  If  such  a  deception  can  be  secured,  it  is 
manifest  that  the  mixing  of  colors  on  which  it  depends  must  take 
jDlace  in  the  brain,  and  not  upon  the  retinas  of  the  two  eyes.  If  a 
white  stripe  be  placed  upon  a  black  surface  and  divided  into  two 
images,  the  right  one  of  which  is  formed  by  looking  at  one  half 
through  blue  glass,  the  left  by  looking  through  gray  glass,  then 
the  right  image  will  be  seen  blue,  but  the  left  will  be  seen  yellow. 
This  is  called  "  binocular  conti-ast  of  colors." 

The  peculiar  perception  of  luminosity  is  due  to  a  struggle  be- 
tween the  two  fields  of  vision  which  results,  not  in  combining  the 
black  images  of  one  field  with  the  white  images  of  the  other  so  as 
to  produce  an  equal  tint  of  gray,  but  in  a  rapid  alternation  of  the 
two.  Very  smooth  bodies,  when  they  reflect  the  light  perfectly, 
do  not  appear  luminous.  But  when  the  surface  of  such  bodies — 
as,  for  example,  the  surface  of  a  sheet  of  water — becomes  ruffled 
by  ripples,  it  becomes  luminous.  The  perception  of  luminosity 
may  be  produced  by  combining  two  stereoscopic  pictures  of  an 
object  which  are  alike  in  contour,  but  one  of  which  is  black  with 
white  hnes  where  the  other  is  white  with  black  lines.  Two  such 
pictures  not  combining  to  produce  an  equal  tint  of  gray  over  the 

'  So  Hering  asserts,  Physiolog.  Optik,  in  Hermann's  Handb.  d.  Physiol., 
III. ,  i. ,  p.  592.    Binocular  mixing  of  colors  lias  been  denied  by  some  authoritiea 


LAWS   OF    CEREBRAL   ACTIOIST.  461 

whole  surface,  the  images  of  the  separate  points  on  the  two  retinas 
enter  into  a  struggle  with  each  other  ;  and  the  rapid  alternation  of 
the  prevalence,  first  of  one  and  then  of  the  other,  gives  rise  to  the 
appearance  of  luminosity. 

Such  phenomena  as  the  foregoing  seem  to  require  a  reference  to 
certain  unknown  processes  in  the  central  organs  as  a  physical  basis 
for  the  psychical  experience.  Some  experimenters  claim  that  in 
these  cases  of  contrast  they  are  able  to  see  either  color  at  will  by 
giving  attention,  first  to  the  image  on  one  retina,  and  then  to  that 
on  the  other.  The  words  in  which  this  claim  is  couched,  however, 
afford  no  explanation  of  the  phenomena  ;  for,  we  repeat  again,  the 
mind  does  not  see  the  image  on  the  retina,  and  cannot  direct  spe- 
cial attentioii^  to  it.  It  can  only  attend  to  this  or  that  feature  of 
the  "presentation  of  sense,"  which  is  in  every  case  a  subjective 
affair.  But  the  very  question  that  we  are  unable  to  answer  con- 
cerns the  reason  why  the  presentations  of  sense  are  constructed  as 
they  are  in  such  cases  ;  the  reply,  so  far  as  any  reply  can  be  given, 
must  be,  that  such  data  or  motifs  furnished  by  the  spatial  series  of 
sensations  as  we  cannot  connect  with  known  laws  of  the  peripheral 
organs  of  sense  must  be  referred  to  unknown  laws  of  the  central  or- 
gans of  the  same  sense.  Apparently  this  truth  holds  good  of  certain 
optical  illusions  of  motion.  The  fact  that  a  steady  succession  of  im- 
ages (as  in  the  case  of  watching  a  fall  of  water),  passing  over  a  partic- 
ular region  of  the  retina  for  a  long  time,  sometimes  ceases  to  be  per- 
ceived as  a  motion,  and  that  the  image  of  a  stationary  body  on  the 
same  retinal  region  may  appear  to  be  moving  in  the  opposite  direc- 
tion, has  been  explained  by  "Thomson's  law."  This  law  refers  the 
phenomena  to  the  principle  of  fatigue.  Recent  investigations,  how- 
ever, seem  to  show  that  the  explanation  is  incorrect.  They  bring 
out  the  remarkable  result  that  the  same  elements  of  the  retina, 
when  stimulated  simultaneously,  may  give  rise  to  imjDressions  both 
of  motion  and  of  rest.  For  this  result  some  unknown  law  of  cere- 
bral action  would  seem  to  afford  the  only  possible  explanation.' 

§  34.  The  fact  that  things  are  seen  upright  and  in  correct  relations 
horizontalh',  by  means  of  data  furnished  through  inverted  retinal 
images,  as  well  as  all  illusions  and  errors  that  are  connected  with 
this  normal  fact,  imjjlies  yet  more  maturity  of  experience.  Why  do 
we  see  the  upper  part  of  the  object  by  means  of  the  lower  part  of  the 
retinal  image,  and  vice  versa  ?  and  why  do  we  see  the  right  side  of 
the  object  by  means  of  the  left  side  of  the  retinal  image,  and  vice 
versa  ?  Such  questions  have  often  been  propounded  as  psycho- 
logical puzzles  of  special  difficulty.  The  only  answer  possible  fol- 
'  See  Journal  of  Physiology,  iii. ,  p.  399  f . 


462  DEVELOPMENT   OF   VISUAL   PERCEPTION'. 

lows,  obviously,  from  the  foregoing  principles.  Strictly  speaking, 
we  neither  see  the  external  object  nor  the  retinal  iruage  ;  the  field 
of  vision  is  a  subjective  affair,  and  is  like  neither  of  these  two.  The 
presentation  of  visual  sense  is  normally  dependent  upon  the  retinal 
image  for  the  data  from  which  it  is  constructed  ;  the  image  is 
dependent  upon  the  external  object  for  its  formation  by  rays  of 
light  reflected  from  the  object  and  converged  upon  the  nervous 
elements  of  the  retina.  The  different  parts  of  the  object  as  seen 
are  primarily  localized  simply  with  reference  to  each  other  by 
means  of  local  retinal  signs  and  of  muscular  sensations  produce,d 
by  motion  of  the  eyes.  But  as  yet  the  field  of  vision  has  no  locality 
in  objective  space  ;  no  part  of  it  can  be  said  to  be  either  up  or 
down,  either  right  or  left.  The  use  of  such  tenns  of  position 
impliea  an  association  of  localized  sensations  of  sight  with  those  of 
touch  and  of  the  muscular  sense,  in  giving  us  a  j)icture  of  the 
relation  of  the  diffei'ent  parts  of  the  body  to  each  other,  and  of  the 
entire  body  to  the  ground,  the  sky,  and  the  various  parts  of  sur- 
rounding objects.  When  the  eyes  are  moved  downward,  the  lower 
parts  of  the  body  and  objects  situated  on  the  ground  successively 
come  into  the  field  of  vision  ;  when  the  eyes  are  moved  upward, 
the  near  ground  and  lower  parts  of  objects  successively  disappear 
from  the  field  of  vision,  and  remoter  or  higher  objects  come  to 
view.  Seeing  objects  to  the  right  or  to  the  left  is  accomplished  by 
motion  of  the  eyes  in  the  corresponding  direction.  Eight  is  the 
direction  in  which  the  right  hand  is  placed  from  the  middle  of  the 
body  ;  left  is  the  direction  in  which  the  left  hand  is  found.  The 
massive  feelings  of  touch  and  muscular  sensation  keep  us  informed 
of  the  general  relation  of  our  bodies  to  the  earth  and  to  objects  on 
its  surface.  The  head  is  the  upper  part,  or  part  farthest  away  from 
the  ground  ;  the  feet  are  the  lower  part,  or  members  of  the  body  in 
contact  with  the  ground.  Thus  we  come  to  use  terms  for  localized 
sensations  of  sight  which,  in  this  use  of  them,  have  no  primary 
reference  whatever  to  the  field  of  vision  in  itself  considered. 

§  35.  The  nature  of  the  "  sense-data"  which  the  mind  has  at  its 
disposal  for  constructing  its  presentations  of  sense,  and  the  psycho- 
physical laws  which  are  followed  in  the  process  of  construction, 
have  been  explained  in  such  detail  that  little  need  be  added  con- 
cerning the  development  of  visual  j)erception.  Visual  space  pre- 
sents itself  to  us  as  a  coherent  complex  of  sensations  of  light  and 
color  systematically  arranged.  The  arrangement  implies  certain 
native  activities  of  the  mind  in  connection  with  and  dependence 
upon  the  action  of  the  nervous  organism  ;  but  it  also  implies  an 
immense  influence  from  experience.     It  is  extremely  difficult,  if  not 


LEARNING   TO   LOCALIZE.  463 

•wholly  impossible,  to  distinguish  with  confidence  the  limits  which 
must  be  drawn  between  what  is  native  and  what  is  learned.  The 
seeing  of  colors  is  undoubtedly  a  far  more  simple  and  primary  act 
than  the  seeing  of  colored  objects  as  situated  in  relation  to  each 
other  in  objective  space.  A  colored  surface,  or  a  system  of  color- 
sensations  related  to  each  other  as  side  by  side  in  space-form,  re- 
sults in  experience  from  the  weaving  together  of  several  spatial 
series  of  sensations.  Such  a  surface  may  theoretically  be  conceived 
of  as  presented  to  the  mind  through  the  activity  of  the  nervous 
elements  belonging  to  the  retina  of  a  single  motionless  eye.  The 
motifs  or  data  which  the  mind  would  have  for  constructing  such  a 
surface  must  be  found  in  the  sei-ies  of  sensations  of  light  and  color 
as  varpng  in  intensity  and  quality  according  to  the  locally  distinct 
nervous  elements  which  are  simultaneously  excited.  The  evidence 
seems,  on  the  whole,  favorable  to  the  assumption  that  some  indefi- 
nite picture  of  visual  space  might  be  gained  wholly  through  the 
excitation  of  a  motionless  nervous  mosaic  (Hke  the  retina)  sensitive 
to  light. 

But  visual  space,  as  experience  makes  it  known  to  us,  requires 
binocular  Adsion  with  moving  eyes.  The  firm  spatial  connection  of 
all  the  parts  requires  that  a  system  of  lines  of  direction  should  be 
fixed,  prescribing  the  objective  points  at  which  the  sensations  pro- 
duced by  exciting  together  the  difierent  paii's  of  the  covering  i^oints 
of  the  retina  must  appear  in  visual  space.  To  establish  such  spatial 
connection,  both  eyes  must  move  in  their  conjoined  action  as  a 
single  organ  of  vision.  By  this  action  the  field  of  binocular  vision 
is  built  up  in  an  order  of  experience  which,  on  the  whole,  consists 
in  the  successive  mastery  of  more  and  more  complex  problems. 
For  the  process  of  learning  to  localize,  the  one  centre — the  point 
of  starting  and  the  goal  of  return — is  the  spot  of  clearest  vision  of 
the  retina  (the  yellow- spot),  to  which  the  point  of  regard  in  the  ob- 
ject corresponds.  With  the  point  of  regard  fixed  in  the  primary 
position  of  the  eye,  the  first  and  most  essential  means  is  gained  for 
orientating  objects  in  the  field  of  vision.  The  meridians,  horizontal 
and  vertical,  and  the  locations  of  different  points  in  the  surface  of 
the  field  of  vision  thus  presented  to  the  mind,  afford  the  compara- 
tively simple  problems  furnished  by  the  primary  position.  In  this 
way  a  central  point,  determining  lines,  and  finally  a  continuous  sur- 
face are  fixed,  to  which  may  be  referred  all  the  directions  and  loca- 
tions of  the  binocular  points  and  lines  of  regard  in  the  secondary 
positions  of  the  eye. 

The  motifs  or  data  which  give  to  the  mind  its  guidance  in 
achieving  its  more  difficult  tasks  are  the  spatial  series  of  muscular 


464  DEVELOPMENT   OF   PERCEPTION. 

and  tactual  sensations  which  are  caused  by  the  motions  of  the  eye 
for  parallel  turning,  for  accommodation,  and  for  convergence  in 
near  vision.  The  general  principle  is,  that  by  motion  the  relative 
space-values  of  the  retinal  elements  are  not  changed  ;  hut  their  ab- 
solute values — that  is,  the  complex  which  is  formed  by  combining 
all  these  muscular  and  tactual  sensations  with  the  local  signs  of  the 
retina — are  changed  in  equal  sense  and  measure.  What  moving  the 
eyes  does  for  the  retinal  images,  moving  the  head  and  body  does 
for  the  presentations  of  sense  as  constructed  in  binocular  vision  ; 
it  alters  the  absolute  values  of  the  complex  of  sensation  as  related 
to  objective  space,  while  keeping  the  relative  values  belonging  to 
the  different  positions  of  the  eyes  unchanged. 

The  visual  perception  of  depth  involves  a  later  and  more  complex 
training  from  experience  than  the  perception  of  two-dimensioned 
extension.  To  solve  the  problem  of  depth,  binocular  vision  with 
moving  eyes,  and  its  resulting  combination  and  separation  of  the 
double  images  of  objects,  seems  necessary.  The  existence  and  as- 
sistance of  those  secondary  helps,  which  are  so  important  in  per- 
ceiving the  solidity  and  distance  of  objects,  imply  a  further  devel- 
opment of  experience.  In  all  these  advances,  however,  the  coirrse 
of  acquisition  is  not  in  separate  straight  lines  that  run  parallel  or 
converge,  as  it  were.  More  complex  experience,  when  obtained, 
modifies  what  is  really  more  simple  and  primary.  What  we  see  in 
monocular  vision  with  an  open  eye,  and  even  what  we  see  with  both 
eyes  closed  and  motionless,  depends  upon  what  we  have  learned  to 
see  with  both  eyes  in  varied  movement  and  availing  themselves  of 
all  possible  secondary  helps.  It  also  depends  upon  what  we  have 
learned  to  know  of  the  nature  and  probable  position  and  shape  of 
manifold  objects  of  which  the  eye  has  already  attained  the  mastery. 

§  36.  Finally,  brief  mention  must  be  made  of  the  connections 
which  are  constituted,  in  the  development  of  our  perception  of  ob- 
jects as  having  the  qualities  and  relations  of  space-form,  by  the 
joint  action  and  mutual  assistance  of  eye  and  hand.  With  the 
sense-presentations  of  one  of  these  senses  the  images  of  objects  as 
known  by  the  other  become  most  intimately  related.  It  is  a  misuse 
of  terms,  however,  and  involves  the  entire  subject  in  confusion,  to 
speak  of  this  joint  product  as  a  "  sense-perception."  It  is  rather  to 
be  spoken  of  as  a  mental  image  or  concept.  The  visual  presenta- 
tion of  an  object — as,  for  example,  a  ball,  a  pen,  a  table — may  re- 
call its  tactual  presentation.  We  readily  interpret  one  into  terms 
of  the  other — sight  into  terms  of  touch,  and  touch  into  terms  of 
sight.  But  all  the  perceptions,  as  such,  of  spatial  proiDerties  and 
relations,  whether  gained  by  eye  or  hand,  are  kept  quite  distinct 


TEANSLATION   OF   PERCEPTIOlSrS.  465 

and  separable  in  the  mind.  No  such  synthesis  takes  place  between 
the  spatial  series  of  the  one  sense  and  the  spatial  series  of  the  other 
sense  as  takes  place  between  the  spatial  series  of  the  same  sense. 
And  aU  the  properties  and  relations  of  bodies  as  known  in  space- 
form  are  given  by  each  of  these  senses.  The  view  which  makes  the 
sense  of  sight  dependent  upon  the  sense  of  touch  and  the  muscu- 
lar sense  for  the  construction  of  its  spatial  objects  is  erroneous. 
While  feehng  the  pen,  we  can  image  how  it  would  look  ;  when 
seeing  it,  how  it  would  feel.  We  can  image  how  much  exertion 
would  be  required  to  reach  a  mountain  which  appears  to  the  eye  so 
far  away,  or  how  a  mountain  would  look  at  a  distance  of  so  many 
miles  as  measured  by  the  exertion  required  to  walk  there.  But  the 
true  presentations  of  the  visual  objects  and  tactual  objects  do  not 
mix  in  one  combined  perception.  They  unite  only  in  one  image  or 
idea  of  the  object. 

§  37.  Interesting  experiments  have  been  conducted  to  determine 
the  degree  of  accuracy  with  which  perceptions  of  distance  by  sight 
can  be  translated,  as  it  were,  into  terms  of  the  tactual  and  mus- 
cular sense.  Some  of  these  experiments  show  the  amount  of  har- 
mony which  can  be  obtained  between  optical  localizing  and  localiz- 
ing with  the  finger.  Helmholtz  *  made  use  of  a  vertical  thread 
which  he  tried  to  locate,  as  seen  in  monocular  vision,  by  hitting  it 
with  a  pencil's  point ;  Donders,^  of  a  very  small  induction-spark, 
which  was  to  be  touched  with  the  index-finger.  The  result  of  50 
experiments,  made  for  distances  along  the  same  line  of  regard  vary- 
ing between  60  and  610  mm.,  when  only  the  spark  itself  was  seen  in 
perfectly  dark  surroundings,  showed  that  the  distance  was  over- 
estimated 34  times,  under-estimated  12,  estimated  right  4  times. 
The  greatest  errors  were  +35  and  —34  mm.  ;  the  mean  error 
10.6  mm.  When  the  suiToundings  were  visible  and  the  electrodes 
seen  with  open  eyes,  the  eyes  then  closed,  and  the  finger  reached 
to  the  estimated  distance,  the  greatest  errors  were  -1-30  and  —12 
mm.,  and  the  mean  variable  error  9.8  mm.,  for  distances  from  80  to 
630  mm.  The  exact  localizing  of  the  point  of  regai'd  in  terms  of 
touch  is  more  difficult  the  farther  the  object  is  removed  and  the 
less  assistance  is  had  from  secondary  helps.  Locahzing  in  the 
same  way  when  the  object  lies  out  of  the  line  of  regard  is  still  more 
inaccurate.  In  29  experiments,  where  the  spark  to  be  localized 
was  flashed  at  a  distance  of  210-600  mm.  to  one  side  of  this  line, 
the  greatest  errors  were  +120  and  —68  mm.,  with  a  mean  error 
of  about  34  mm. 

'  Physiolog.  Optik,  p.  650. 
2  Archiv  f.  Ophtlialmologie,  XVII.,  ii.,  p.  55. 
30 


466  DEVELOPMENT   OF   PERCEPTIOlSr. 

The  problem  of  comparing  tlie  judgments  of  linear  extension 
made  by  the  eye,  the  hand,  and  the  arm,  and  of  determining  their 
relative  accuracy,  has  recently  been  examined,  experimentally,  at 
considerable  length  by  J.  Jastrow.'  His  method  was  to  present  a 
definite  length,  varying  from  5  mm.  to  120  mm.,  to  the  retina,  the 
skin  (by  application  of  a  pair  of  points,  or  by  motion  of  a  single 
point),  to  the  forefinger  and  thumb  (by  being  held  between  the 
two),  or  to  the  arm  when  in  free  movement  and  guiding  a  pencil  to 
express  its  estimate.  The  subject  of  experiment  was  required  to 
get  a  clear  perception  of  the  given  distance  by  one  of  these  organs 
(called,  in  such  case,  the  "  receiving  sense  "),  and  then  either  si- 
multaneously or  successively  exj)ress  this  perception  through  the 
same  or  some  other  one  of  these  organs  (the  "  expressing  sense  "). 
In  this  manner  it  was  discovered  that,  if  the  eye  is  both  receiving 
and  expressing  sense,  small  lengths  will  be  under-estimated  and 
large  lengths  exaggerated,  the  point  where  no  error  is  made  being 
at  about  38  mm. ;  whereas,  if  the  hand  is  both  receiving  and  ex- 
pressing, small  lengths  will  be  exaggerated  and  large  lengths  un- 
der-estimated, the  "indifference-point"  being  at  about  50  mm.  ; 
but  the  arm  exaggerates  all  lengths  within  the  limits  of  the  experi- 
ments. When,  however,  the  eye  expresses  and  the  other  organs 
receive  the  impression,  all  lengths  are  greatly  under-estimated  ;  but 
if  the  hand  is  the  expressing  sense,  all  lengths  are  greatly  exagger- 
ated. The  arm  as  expressing  sense  exaggerates  all  lengths  received 
by  the  eye,  and  under-estimates  all  received  by  the  hand. 

The  relative  accuracy  of  the  three  senses,  whether  receiving  or 
expressing,  or  both,  stands  in  the  order  of  eye,  hand,  arm — the  hand 
being  only  slightly  better  than  the  arm.  The  degree  of  confidence 
felt  in  the  estimate  made  is  naturally  greatest  where  the  accuracy 
is  greatest.  Inasmuch  as  "  the  expressing  sense  gives  the  charac- 
teristic properties  to  the  curve  of  error, '"^  the  question  arises 
whether  all  the  phenomena  cannot  be  accounted  for  by  a  special 
application  of  the  law  of  habit  in  connection  with  the  normal  action 
of  the  sensory  apparatus.  Each  sense,  when  expressing  the  esti- 
mate, tends  to  approximate  it  in  size  toward  those  dimensions  which 
it  is  most  accustomed  to  judge  accurately. 

All  the  foregoing  results  show  plainly  that  the  interpretation  of 
visual  distance  in  terms  of  the  tactual  and  muscular  sense  is  a  mat- 
ter of  complex  experience,  and  is  not  usually  more  than  very  im- 
perfectly attained.     It  bears  little  comparison  with  the  nicety  of 

'  Art.  on  The  Perception  of  Space  by  Disparate  Senses,  in  Mind,  October, 
1886.  pp.  539-554. 
=  Ibid.,  p.  549. 


MIND   AS   PSYCHICAL   SUBJECT.  467 

the  spatial  perceptions  belonging  to  each  one  of  the  two  senses 
concerned  when  interpreting  its  own  specific  data  in  corresponding 
terms,  as  it  were. 

§  38.  In  closing  this  subject,  the  one  psychological  truth  of  pre- 
eminent value  which  has  been  most  obviously  demonstrated  should 
be  stated  again.  Perception  is  the  result  of  an  extremely  complex 
activity  of  the  psychical  subject,  Mind;  it  involves  the  synthesis  of 
a  number  of  sense-data  according  to  laws  that  are  not  deducible 
from  the  nature  of  the  external  objects,  or  of  the  physiological  ac- 
tion of  the  end-organs  and  central  organs  of  sense.  An  analysis  of 
these  data  themselves  is  not  sufficient  to  explain  perception.  The 
descriptions  of  Physiological  Psychology  can  do  no  more  than 
enumerate  these  data,  show  their  dependence  on  external  stimuli, 
and  the  value  which  they  have  as  motifs  for  the  perceiving  subject ; 
and  then  understand  the  laws  of  this  synthesis  as  the  permanent 
modes  of  the  behavior  of  the  psychical  subject.  The  object  of 
sense-perception,  the  presentation  of  sense,  is  not  an  extra-VLXQnisl 
entity  made  up  outside  of  the  mind  and  borne  into  or  impressed 
upon  it  thi'ough  the  avenues  of  sense.  It  is  a  mental  construction. 
The  field  of  vision  is  a  subjective  affair,  and  so  is  the  field  of  touch. 
The  same  psychical  subject  which  reacts  upon  the  stimulation  of 
the  nervous  organs  of  sense  in  the  form  of  sensations,  by  its  activity 
in'  synthesizing  these  sensations,  constructs  the  objects  of  sense. 
The  fundamental  fact  is  the  presence  and  activity  of  the  subject, 
known  as  Mind. 


CHAPTER  VIII. 

TIME-EELATIONS   OF  MENTAL  PHENOMENA. 

§  1.  "  Pkesentations  of  sense  "  appear  in  consciousness,  not  only 
as  having  spatial  qualities  and  relations,  but  also  as  occurring  either 
simultaneously  or  successively  as  respects  Time-form.  The  clear- 
est expeiience  of  the  manner  in  which  our  sensations  are  located  in 
this  framework  of  time,  as  it  were,  is  gained  by  attention  to  the 
successive  notes  of  a  melody,  or  to  the  rhythm  of  visual  or  mus- 
cular impressions  which  accompanies  a  regularly  recurrent  motion 
of  some  member  of  the  body.  What  is  true  of  the  presentations 
of  sense  is  also  true  of  all  mental  phenomena,  of  the  reproduced 
images  of  sense,  of  pure  creations  of  fancy,  and  of  thoughts.  All 
have  that  form  of  occurrence  and  relation  which  we  call  "  Time." 

Physiological  Psychology,  however,  can  no  more  give  an  ultimate 
explanation  of  this  time-form  which  belongs  to  all  mental  phenom- 
ena than  of  the  space-form  which  objects  of  sense  acquire  as  the 
result  of  a  mental  synthesis.  Experimental  science  cannot  explain 
"time."  Nothing  is  accomplished  toward  comprehending  the  ori- 
gin of  the  mental  representation  of  time  by  indicating  the  speed, 
number,  and  order  of  the  various  series  of  conscious  experiences. 
Successive  presentations  of  sense  or  successive  ideas  do  not  of 
themselves  constitute  a  mental  presentation  or  idea  of  succession. 
The  idea  that  a  follows  or  precedes  h  is  not  the  idea  of  a  nor  the 
idea  of  h  ;  neither  is  it  the  idea  of  a  -f  6  or  of  a  —  h.  Experimental 
science  can  explain  the  order  of  succession ;  but  in  doing  this  it 
imphes  the  idea  of  succession,  and  this  idea  is  not  itself  a  succes- 
sion, or  an  order  of  succession,  or  a  compound  of  successive  ideas.' 

Many  thousands  of  experiments  have  been  made  (since  the  work 
of  Donders  in  1868),  with  the  use  of  the  most  comiDlicated  and  deli- 
cate machinery,  in  order  to  fix  the  amount  of  time  required  for  the 
various  processes,  both  nervous  and  mental,  which  are  the  condi- 
tions of  our  conscious  life.  These  experiments  have  succeeded  in 
bringing  many  interesting  facts  to  light.  But  the  laws  thus  estab- 
lished beyond  all  reasonable  question  are  remarkably  few  ;  more- 
'  Comp.  Volkmann  von  Volkmar,  Lelirb.  d.  Psychologic,  II.,  p.  11  f. 


METHODS   OF   MEASUEEMENT.  469 

over,  they  are  nearly  all  merely  restatements  in  more  definite  form 
of  familiar  generalizations.  That  a  kind  of  sluggishness  or  inertia, 
which  the  stimulus  must  overcome,  belongs  to  all  the  senses,  and 
that  they  often  continue  to  act,  when  once  roused,  after  the  excit- 
ing cause  is  withdrawn ;  that  different  sensations  following  each 
other  too  quickly  tend  to  confuse  or  destroy  each  other ;  that  no 
one  can  see  or  think  more  than  about  so  rapidly,  but  that  this  rate 
varies  with  different  individuals  and  with  the  same  individual  at 
different  times  ;  that  it  takes  more  time  to  perceive  or  think  where 
the  objects  are  complex,  and  are  either  too  small  or  too  large  or 
too  closely  alike  ;  that  it  takes  time  to  will  or  choose,  less  time  to 
act  when  we  know  what  to  expect,  and  more  time  to  move,  in  re- 
sponse to  a  particular  sensation,  some  part  of  the  body  which  we 
are  not  accustomed  to  connect  with  that  sensation  ;  that  practice 
increases  the  speed  of  our  mental  and  bodily  action,  and  that  fatigue 
and  certain  drugs  diminish  it>— ail  these  statements  are  matters  of 
common  observation. 

§  2.  It  is  not  necessary  to  describe  the  construction  of  the 
machines  which  have  been  used  in  experimenting  upon  the  time- 
relations  of  mental  phenomena,  or  the  methods  of  using  them  em- 
ployed and  commended  by  different  observers.  The  general  prob- 
lem is  in  all  cases  essentially  the  same — namely,  to  produce  certain 
definite  impressions  upon  the  organs  of  sense,  to  secure  a  definite 
result  in  the  form  of  motion  of  some  part  of  the  body  as  a  sign 
that  the  impressions  have  been  received  (aud,  perhaps,  interpreted 
and  mentally  combined),  and  to  measure  with  extreme  accuracy  the 
interval  between  peripheral  stimulation  and  resulting  motion. 

The  electrical  current  is  ordinarily  used  to  mark  both  the  in- 
stant when  the  external  sense-stimulus  acts  on  the  organ  and  that 
when  the  resulting  motion  occurs.  The  stimulus  may  consist  in 
the  flash  or  crackle  of  an  electric  spark,  the  appearance  of  one 
or  more  colors  or  figures,  or  letters  or  words,  the  sounding  of  a 
bell  or  a  falhng  ball,  etc.  ;  the  motion  may  be  with  the  finger 
pressing  a  key,  or  the  foot  or  hand  closing  or  breaking  a  circuit, 
or  the  vocal  organs  calling  into  a  tube,  etc.  The  one  difficult 
matter  which  marks  the  success  or  the  comparative  failure  of  any 
series  of  observations  is  the  arrangement  of  the  experiments  and 
their  tabulated  results  so  as  to  analyze  the  difterent  elements  of  the 
complex  process  involved.  Such  experiments  need  to  be  repeated 
many  times  upon  the  same  individual,  so  as  to  eliminate  the  vari- 
able factors  of  bodily  condition,  attention  or  distraction  of  mind, 
practice,  etc.  ;  they  need  also  to  be  repeated  vdth.  many  individuals, 
so  as  to  calculate  upon  the  so-called  personal  equation. 


470  THE  FIXING    OF   EEACTION-TIME. 

§  3.  The  interval  between  the  instant  when  the  external  stimulus 
begins  to  act  ujDon  the  end-organ  of  sense  and  the  resulting  move- 
ment of  some  member  of  the  body  has  been  called  "  physiological 
time"  by  Hirsch  and  others,  and  "reaction-time"  by  Exner.  The 
latter  term  is  preferable.  Reaction- time  is  "  simple  "  when  all  the 
elements  which  tend  to  complicate  the  processes  involved  in  the  re- 
action, and  so  to  lengthen  the  time  required  by  it,  have  been  as  far 
as  possible  ehminated.  Reaction  obtained  in  response  to  a  single 
sensation  of  known  quality,  the  instant  of  whose  appearance  is  ex- 
pected, by  executing  a  single  natui-al  and  easy  motion,  best  fulfils 
the  conditions  of  simphcity.  It  is  therefore  requisite,  for  all  ex- 
periments of  this  sort,  that  the  average  simple  reaction-time  of  each 
individual  experimented  upon  shall  be  determined  ;  and  also  the 
effect  of  practice,  exhaustion,  and  other  influences  ujDon  this  inter- 
val. But  even  the  simplest  reaction-time  is,  of  course,  a  very  com- 
plex affair. 

Donders  '  distinguished  no  less  than  twelve  different  processes 
as  entering  into  "physiological  time"  (or  simple  reaction-time)— 
and  this  without  interpolating  any  purel}^  psychical  elements,  as 
occupying  separate  periods,  into  the  entire  interval.  The  analysis 
of  Exner  '^  is  more  pertinent  to  our  purpose.  Exner  finds  seven 
elements  in  all  reaction-time  :  (1)  An  action  of  the  stimulus  on  the 
end-organ  of  sense  preparatory  to  excitation  of  the  sensory  nerve  ; 
(2)  centripetal  conduction  in  this  nerve  ;  (3)  centripetal  conduction 
in  the  spinal  cord  or  lower  parts  of  the  brain  ;  (4)  transformation 
of  the  sensory  into  the  motor  impulse ;  (5)  centrifugal  conduction 
of  the  impulse  in  the  spinal  cord  ;  (6)  centrifugal  conduction  in 
the  motor  nerve  ;  (7)  setting-free  of  the  muscular  motion.  Of 
these  seven  factors,  however,  the  fourth  is  most  interesting  to  psy- 
chology. It  may  properly  be  called  "  psycho-physical  "  as  distin- 
guished from  more  purely  physiological  time.  The  other  six  ele- 
ments (with  the  exception  of  the  first,  on  account  of  difficulties 
inherent  in  the  experiments)  have  been  determined  with  some  de- 
gree of  definiteness  (see  Part  I.,  chap,  iii.,  on  the  speed  of  nervous 
processes).  It  is,  then,  theoretically  possible  to  ascertain  the  amount 
of  these  six  and  subtract  them  from  the  entire  reaction-time  ;  the 
remainder  would  be  the  interval  occupied  by  the  central  cerebral 
processes  (that  is,  by  No.  4).  Thus  Exner  ^  assumes  62  meters 
per  second  as  the  probable  rate  of  conduction  in  both  sensory 
and  motor  nerves  ;  and  in  the  spinal  cord,  8  for  the  sensory  and 

'  Archiv  f.  Anat. ,  Physiol.,  etc.,  1868,  p.  664. 

^  See  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  271. 

3  Ibid.,  p.  272  f. 


ELEMENTS   OF   PSYCHO-PHYSICAL   TIME.  471 

11-12  for  the  motor  process.  He  thus  calculates  that  about  0.0828 
sec.  is  the  "reduced  reaction-time,"  or  interval  occupied  within 
the  cerebral  centres  in  transforming  the  sensoiy  into  motor  im- 
pulses— in  the  special  case  of  reaction  from  hand  to  hand,  where 
the  whole  reaction-time  is  0.1337  sec.  The  uncertainties  of  all 
such  calculation,  however,  occasion  the  demand  for  other  methods 
of  determining  the  strictly  "  psycho-physical  "  portion  of  reaction- 
time. 

§  4.  "Psycho-physical  time"  (No.  4  of  Exner's  seven  processes) 
is  analyzed  by  Wundt '  into  three  psycho-physical  processes  :  (1) 
Entrance  into  the  y'lsnal  field  of  consciousness,  or  simple  perception ; 
(2)  entrance  into  the  point  of  clear  vision  with  attention,  or  apper- 
ception (attentive  and  discerning  perception) ;  (3)  the  excitation  of 
the  will,  which  sets  free  in  the  central  organ  the  registrating  mo- 
tion. Obviously,  the  mental  processes  are  here  all  conceived  of 
after  the  analogy  of  sight.  Consciousness  is  regarded  as  a  field  of 
vision  ;  objects  enter  it  and  are  at  first  only  obscurely  and  indefi- 
nitety  perceived,  as  are  those  visual  objects  whose  images  enter  the 
field  of  the  eye  at  the  sides  of  the  retina.  Time  is  required  for  the 
objects  to  arrive  at  the  spot  of  clear  vision — the  fovea  centraliH  of 
consciousuess  [Blickpunkt) — where  discerning  attention  is  bestowed 
upon  them  and  they  are  opperceived.  "When  they  are  apperceived, 
further  time  is  required  to  get  up  the  corresponding  molecular  mo- 
tion in  the  motor  areas  of  the  brain.  All  three  foregoing  processes 
are  psj'cho-physical — that  is,  they  comprise  physiological  processes 
in  the  central  organs  and  simultaneous  corresponding  changes  of 
consciousness  occurring  in  time-form.  There  is  no  good  reason  to 
suppose  that  the  mind  occupies  time  for  its  own  processes  which  is 
separate  from  and — as  it  were — thrown  in  between  the  physio- 
logical processes.  Indeed,  all  the  evidence  is  contrary  to  such  an 
hypothesis. 

Wundt  has  made  an  elaborate  defence  of  his  positions  with  re- 
gard to  the  nature  of  psycho-physical  time.  He  and  his  pupils 
have  attempted  more  definitely  to  characterize  the  cerebral  changes 
which  correspond  to  each  of  the  mental  elements  of  (1)  perception, 
(2)  apperception,  and  (3)  wall.  His  figure  of  speech,  which  likens 
all  changes  of  conscious  states  to  those  produced  by  moving  an 
image  over  the  retina  to  the  spot  of  clear  vision,  may  be  accepted 
as  helpful  to  the  imagination  ;  it  must  not  be  forgotten,  however, 
that  it  is  still  a  figure  of  speech.  The  fact  of  which  it  takes  account 
is,  that  all  changes  of  consciousness  require  tim.e  in  order  to  define 
themselves  with  their  maximum  of  clearness  and  intensity.  The 
'  Physiolog.  Psychologie,  ii.,  pp.  330  fE. 


472  THE   FIXIIS^G   OF   EEACTIOIST-TIME. 

position  that  the  mental  forms  of  perception,  apperception,  and 
will,  are  exactly  simultaneous  with  corresjooncling  cerebral  processes, 
and  that  mental  states  are  not  to  be  regarded  as  forming  them- 
selves in  a  separate  time,  as  it  were,  on  top  of  these  processes,  may 
also  be  admitted  in  a  provisional  way.  It  is  probable  theory,  how- 
ever, rather  than  demonstrated  fact.  Accordingly,  the  first  problem 
of  psychometry  is,  to  determine  the  simple  reaction-time,  and  from 
it  to  find  the  three  factors  of  psycho-physical  time — namely,  per- 
ception-time, apperception-time  (or  discernment-time),  and  will- 
time. 

§  5.  Any  psycho-physical  theory  of  the  time-relations  of  mental 
phenomena  requires  that  account  should  be  taken  of  the  inertia 
of  the  nervous  system.  As  composed  of  moving  molecules,  it  ne- 
cessarily requires  some  time  to  be  started  by  the  action  of  a  given 
stimulus,  then  reach  its  maximum  of  activity  in  a  particular  direc- 
tion, then  subside  into  a  negative  condition  with  respect  to  this 
direction  (called  "Anklingen"  and  "Abklingen"  of  the  nervous 
excitement,  by  the  German  investigators).  This  statement  follows 
as  a  necessary  assumption  from  the  physical  nature  of  the  nerve- 
fibres  and  nerve-cells,  since  iuertia  is  a  propei-ty  of  every  material 
mechanism.  It  is  difficult,  however,  to  justify  the  assumption 
experimentally,  or  to  fix  the  exact  amount  of  time  consumed  by 
the  inertia  of  different  parts  of  the  nervous  system.  Experiment 
demonstrates  no  stadium  of  latent  excitation  for  the  motor  nerve, 
such  as  is  about  yig-  sec.  for  the  muscle  when  electricity  is  used. 
The  case  is  different,  however,  Avith  the  end-organs  of  sense.  They 
do  exhibit  a  certain  sluggishness,  and  this  is  one  reason  why  only 
so  many  sensations  in  a  given  unit  of  time  can  be  produced  by 
their  successive  irritation. 

The  result  of  the  inertia  of  the  end-organs,  as  determining  the 
number  of  separate  excitations  of  which  they  are  capable  in  a 
second,  varies  for  the  different  senses.  The  nerve-endings  of  touch 
probably  exceed  all  others  in  the  promptness  with  vdiich  they  re- 
sjiond  to  stimulus  and  then  return  to  a  relative  equilibrium.  But 
the  number  of  separate  sensations  of  this  sense  which  can  be  pro- 
duced during  a  given  interval  depends  in  a  remarkable  way  upon 
the  quality  and  intensity  of  the  stimulus,  the  place  where  it  is  ap- 
plied, etc.  The' results  of  different  experimenters  therefore  differ 
widely.  Preyer  thought  that  27.6-36.8  nervous  shocks  (per  sec- 
ond) of  the  skin  fused  into  one  continuous  sensation  ;  but  Valentin 
put  the  limit  at  480-640,  and  von  Wittich '  succeeded  in  distinguish- 

'  For  his  remarks  on  Preyer' s  experiments,  see  tlie  article  in  Pfliiger's  Archiv, 
ii.,  pp.  329  ff. 


STATEMENT   OF  TALBOT'S   PRINCIPLE.  473 

ing  about  1,000  separate  excitations  in  this  unit  of  time.  Hearing 
can  receive  nearly  as  many  separate  sensations  in  a  second  as  can 
touch.  The  noise  of  the  electric  spark  has  been  heard  with  one  ear 
only,  as  separate  sensations,  at  intervals  of  0.00205  sec;  but  hardly 
or  not  at  all  at  intervals  of  0.00198  sec.  The  number  of  possible 
sensations  of  sound  may  then  be  placed  at  about  500  per  second. 
Mach, '  however,  by  using  the  click  from  a  revolving  toothed- wheel, 
claims  to  have  reduced  the  interval  to  0.016  sec.  The  interval 
is  increased  to  about  0.064  sec.  when  the  same  auditory  impres- 
sions are  heard  by  both  ears.  E.  H.  Weber  noticed  that  we  can 
tell  whether  two  watches  are  ticking  exactly  together  mucli  better 
when  both  are  held  near  the  same  ear  than  when  one  is  held  at 
each  ear.  Far  fewer  musical  tones  than  noises  can  be  heard  in  a 
second  ;  and,  indeed,  a  number  of  vibi'ations,  occupying  a  consider- 
able fraction  of  a  second,  must  be  secured  before  the  sensation  of 
tone  is  established,  as  it  were. 

The  smallest  interval  for  sensations  of  sight,  when  the  two  stimuli 
act  on  the  same  place  of  the  retina,  is  still  greater.  In  ordinary 
daylight,  rotating  disks  whose  surface  is  part  white  and  part  black 
become  gray  (that  is,  the  sensations  fuse)  when  they  attain  a  motion 
of  about  24  per  second.  It  can  be  told  which  of  two  images  of  elec- 
tric sparks  that  are  0.011  mm.  apart  on  the  retina  occurs  first,  if 
the  difference  in  the  time  of  their  occurrence  is  0.044  sec.  If  the 
two  sparks  are  seen  as  one  with  an  apparent  motion,  its  direction 
can  be  distinguished  when  the  two  ends  of  the  Une  of  motion  are 
only  0.014-0.015  sec.  apart.  But  if  one  stimulus  strikes  the  fovea 
centralis  and  the  other  a  point  of  the  retina  6  mm.  off,  the  smallest 
interval  for  distinct  perception  is  increased  to  0.076  sec."  Within 
certain  limits  these  intervals  are  independent  of  the  intensity  of  the 
light,  when  it  falls  on  the  retina  near  its  centime  ;  but  (comp.  p.  334) 
the  intensity  and  quality  of  the  sensations  are  connected  with  the 
time  during  which  the  stimulus  acts.  The  law  for  the  "  time- 
course  "  of  such  retinal  excitations  has  been  stated  and  defended  by 
Fick,^  as  known  by  the  name  of  "  Talbot's  principle  :"  If  any  place 
of  the  retina  is  periodically  excited  with  light  of  given  intensity,  for 
a  certain  time  a,  and  then  left  unexcited  for  a  time  h,  and  if  the 
time  (2  -f  6  is  less  than  about  0.04  sec,  then  the  sensation  becomes 

continuous,  with  a  strength  corresponding  to  the  excitation  — — -7- 

'  Sitzgsber.  d.  Wiener  Acad.,  LI.,  p.  142. 

^  Comp.  Exner,  in  Hermann's  Handb.  d.  Physiol.,  II.,  ii. ,  p.  256  f. ;  and 
Sitzgsber.  d.  Wiener  Acad.,  LXXII.,  fi.  156  f. 

2  Archiv  f.  Anat.,  Physiol.,  1863,  p.  739  f. ;  and  Hermann's  Handb.  d.  Pby 
siol.,  IIL,  i.,  p.  212  f. 


474  THE   FIXING   OF   EEACTION-TIME. 

If  the  inertia  of  the  eye  for  the  different  color-sensations  were 
greatly  different,  we  would  see  objects  differently  colored  accord- 
ing to  the  time  that  the  rays  from  them  were  acting  on  the  retina. 
That  the  different  parts  of  the  spectrum  do  actually  require  slightly 
different  intervals  of  time  to  reach  the  maximum  of  their  excitation 
has  been  shown  by  Kunkel. '  Equally  bright  light,  as  before  stated 
(p.  334),  attains  its  maximum  effect,  for  red  rays  in  about  0.0573 
sec,  for  green  in  0.133  sec,  for  blue  in  0.0916  sec.  With  the  same 
color-tone,  the  greater  the  brightness  the  quicker  the  maximum 
effect  is  reached.  Thus  for  three  degrees  of  brightness  the  time  for 
red  rays  is  0.0573-0.071  sec  ;  for  green,  0.0699-0.133  sec  ;  for  blue, 
0.0916-0.102  sec.  Accordingly,  the  spectrum  may  be  reduced  in 
size  and  number  of  color-tones  by  diminishing  the  duration  of  the 
action  of  the  light  which  forms  it. 

The  measurement  of  the  smallest  intei'val  for  sensations  of  smell 
and  taste  cannot  be  made  with  satisfactory  exactness  on  account  of 
the  nature  of  the  stimuli  of  these  senses.  Little  is  known  which 
goes  beyond  ordinary  experience  concerning  after-tastes  analogous 
to  the  after-images  of  the  eye.  One  experimenter  (Bidder)  thought 
that  the  sensation  continued  after  the  tongue  had  been  so  carefully 
dried  off  that  no  particles  of  thetastable  substance  were  left  remain- 
ing ;  but  of  this  we  can  scarcely  be  sure.  It  may  be  that  certain 
substances  leave  their  after-taste  because  their  tastable  particles  are 
dissolved  later ;  or  because  their  effect,  being  weaker,  is  at  first 
suppressed  by  particles  of  stronger  quality.^ 

§  6.  When  the  successive  sensations  are  of  different  senses,  the 
"  smallest  interval  "  between  them,  and  so  the  number  j^ossible  in 
a  second,  varies  still  more.  The  following  table  ^  exhibits  the  re- 
sults obtained  by  several  different  observers  : 

Sec. 
Between  two  sensations  of  sound  (electrical  sparks) 0.002 

Between  two  sensations  of  liglit  (direct  electrical  excitation  of  same 

retinal  spot) 0.017 

Between  two  sensations  of  toucli  (impact  on  finger — Macli) 0.0277 

Between  two  sensations  of  light  {a,i fovea  centralis,  by  optical  images). .  0.044 
Between  two  sensations  of  light  (at  periphery  of  retina,  by  optical  images)  0. 049 
Between  sensation  of  sight  and  sensation  of  touch  (sight  following)   . . .   0.05 
Between  sensation  of  sight  and  sensation  of  hearing  (sight  following). .   0.06 

Between  two  sensations  of  noises  (each  heard  by  one  ear) 0.064 

Between  sensation  of  sight  and  sensation  of  touch  (sight  preceding) . . .   0.071 
Between  two  sensations  of  light,  one  at  the  periphery  and  the  other  at 

the  centre  of  retina 0. 076 

Between  sensation  of  sight  and  sensation  of  hearing  (sight  preceding) ...  0. 16 

^  Pflliger's  Archiv,  ix. ,  p.  206  f. 

^  Comp.  von  Vintschga>i,  in  Hermann's Handb.  d.  Physiol.,  III.,  ii. ,  p.  221 

^  By  Exner,  in  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  262. 


EEACTION  FROM   HAND   TO   HAND. 


475 


Fig.  114. — Curves  showing  the  Rise  and  Fall  of 
the  Intensity  of  Sensations  of  Light — ihe  ab- 
cissas  measured  along  a-d  representing  the 
time. 


§  7.  The  way  that  the  intensity  of  sensations  of  light  rises  to  a 
maximum,  continues  there,  and  then  falls  off  through  exhaustion 
of  the  retina,  in  time,  has  been 
represented  by  Fick '  with  the 
use  of  the  accompanying  figure 
(No.  114). 

§  8.  The  point  of  starting  for 
determining  experimentally  all 
the  jDroblems  which  concern  the 
durations  and  relations  in  time 
of  mental  phenomena  is  gained 
by  fixing  the  "  simple  reaction- 
time.  "  This  is  found  to  vary  for 
different  persons,  for  the  differ- 
ent senses,  and  under  different  conditions  of  expectation,  attention, 
habit,  etc.  In  its  very  simplest  form,  the  question  may  be  stated  as 
follows  :  How  long  an  interval  will  elapse,  under  the  most  favorable 
cu'cumstances,  between  the  instant  when  some  end-organ  of  sense  is 
stimulated  and  the  instant  when  motion  follows  as  the  result  of  rec- 
ognizing the  fact,  in  consciousness,  that  such  stimulation  has  taken 
place  ?  In  this  form  the  three  elements  of  psycho-physical  time 
(perception,  discernment  or  apperception,  and  choice)  are  sup- 
posed to  be  reducible  to  one — namely,  to  simple  perception.  This 
supposition  is,  of  course,  true  only  in  case  that,  by  practice  in  react- 
ing upon  an  expected  sensation  in  one  definite  way,  the  cerebral 
sensory-motor  processes  have  attained  the  highest  possible  rate  of 
speed,  and  the  time  ordinarily  occupied  in  deciding  what  to  do,  and 
in  starting  the  voluntary  motor  mechanism,  has  been  reduced  al- 
most, or  quite,  to  zero.^  The  entire  process  then  becomes  reflex, 
simply  the  sensory  central  part  of  it  being  represented  by  a  con- 
scious act  of  perception.  To  shorten  the  reaction-time  as  much 
as  possible,  the  subject  of  the  experiment  must  know  what  place  of 
the  sensory  organism  is  to  be  hit  by  the  stimulus,  and  about  when 
to  look  out  for  it ;  he  must  also  be  called  upon  to  react,  in  one  and 
the  same  easy  and  natural  way,  in  aU  cases,  as  soon  as  he  knows 
that  he  is  hit  at  all. 

The  following  table '  gives  the  mean  values  of  the  reaction-time 
"from  hand  to  hand  "  (one  hand  being  hit  by  the  electrical  cui-rent 

I  Hermann's  Haudb.  d.  Physiol.  HI.,  i.,  p.  216. 

^  Comp.  Wundt,  Physiolog.  Psychologie,  ii.,  p.  226  f. 

3  Taken  from  Exner,  in  Hermann's  Handb.  d.  Physiol.,  II.,  11.,  p  263;  the 
two  sets  of  numbers  indicate  values  which  were  found  iu  two  series  of  exper- 
iments. 


476  THE   FIXING   OF   EEACTIOlSr-TIME. 

and  the  other  reacting,  for  example,  to  press  a  key),  as  determined 
by  various  observers  : 

,^.      ,  ^  ,  ,  .  Von  Ti  Von       Von  Kries  and 

Helmholtz.  Hirsch.        Kohlrausch.       -^ittich.  ^^^ier.         vintschgau.     Auerbach. 

0.12776  sec.  I  0.1733  sec.  )  n  ifiQ7  =«^   I  0-153  sec.  )  0.1376  sec.  )  0. 1087  sec.  I  0.117  sec. 
0.12495  sec.  \  0.1911  sec.  \  "-^"^'  ^^°-  f  0.166  sec.  J  0.1283  sec.  (  0.1860  sec.  j  0.146  sec. 

The  last  two  experimenters  developed  certain  interesting  results. 
They  found  the  reaction-time,  when  the  stimulus  was  applied  to 
the  middle  finger,  to  be  for  Kries  0.117  sec.  and  for  Auerbach  0.146 
sec.  ;  but  when  applied  to  the  back  of  the  hand,  to  be  for  Kries 
0.119  sec.  and  for  Auerbach  0.147  sec.  But  the  hand  being  about 
16  ctm.  nearer  the  brain  than  the  middle  finger,  its  reaction-time 
should  have  been  some  0.004  sec.  shorter  instead  of  longer,  as  a 
matter  of  physiological  time.  Esner  found  that  the  reaction-time, 
when  the  forehead  is  stimulated,  is  greater  than  when  the  stimulus 
is  applied  to  the  hand.  Bloch  found  the  same  thing  true  when  the 
nose  is  stimulated.  The  intercerehral  relations,  taken  in  connection 
with  the  law  of  habit,  probably  account  for  the  foregoing  facts. 

The  value  of  the  reaction-time  also  changes  when  the  character 
of  the  stimulus  is  changed  on  which  the  subject  of  experiment  re- 
acts.    This  fact  is  made  apparent  by  the  following  table  : ' 

Observer.  Optical  stimulus.    Acoustic  stimulus.     Stimulus  of  touch. 

Sec.  Sec.  Sec. 

Hirscli  0.200  0.149  0.182  (hand). 

Hankel 0.225  0.151  0.155 

Bonders 0.188  0.180  0.154  (neck). 

Von  Wittich 0.194  0.182  0.130  (forehead). 

Wuudt 0.175  0.128  0.188 

Exner 0.1506  0.1360  0.1276  (hand). 

Auerbach 0.191  0.122  0.146 

VonKries 0.193  0.120  0.117 

We  conclude,  then,  that  under  the  most  favorable  circumstances 
the  reaction-time  can  scarcely  be  reduced  to  y^o"  o^  ^  second,  while 
it  rarely  rises  much  above  y\  of  a  second. 

§  9.  It  has  been  argued  that  the  apparent  difference  in  the  reac- 
tion-times of  different  senses  is  due  to  difference  in  the  intensity  of 
the  stimuli  applied.  Increasing  the  strength  of  the  stimulus  de- 
creases the  reaction-time  in  all  the  senses  ;  but  we  have  no  veiy 
good  means  of  measuring  stimuli  of  one  sense  in  terms  of  another 
sense.  It  has  been  proposed  ^  to  reduce  them  to  a  common  standard 
by  referring  the  sensations  to  the  point  where  they  barely  reach 
the  "  threshold  of  excitation "  (Heizschivelle)  ;  that  is,   where  they 

'  Taken  from  the  article  of  von  Kries  and  Auerbach,  Archiv  f.  Anat.  u.  Phy- 
siol., Physiol og.  Abth.,  1877,  p.  359  f. 

'^  By  Wundt,  Physiolog.  Psychologic,  ii.,  p.  223  f. 


EFFECT   OF   INCliEASED   INTENSITY. 


477 


are  just  perceptible  in  consciousness.  In  this  way  the  mean  result 
for  sound  (0.337),  light  (0.381),  and  touch  (0.327)  are  found  to  be 
almost  exactly  the  same.  It  has  further  been  argued  that  the 
speed  of  perception  and  the  duration  of  psycho-physical  time  are 
the  same  for  all  the  senses.  On  the  contrary,  there  seems  good 
reason  to  suppose  that  the  reaction-time  of  sight  is  necessarily 
longer  than  that  of  hearing  or  touch,  on  account  of  the  photo- 
chemical natui'e  of  its  more  immediate  stimulus.  One  observer 
(von  Wittich)  has  even  gone  so  far  as  to  conjecture  that  the  speed 
of  conduction  in  the  optic  nerve  is  less  than  that  of  the  other 
nerves  of  sense  ;  it  is  rather  to  be  concluded,  however,  that  the  la- 
tent time  of  the  sensory  end -apparatus,  and  of  the  cerebral  pro- 
cesses by  which  sensory  impulses  pass  over  into  motor  impulses,* 
is  different. 

§  10.  The  effect  of  increasing  the  intensity  of  the  stimulus,  in  di- 
minishing the  reaction-time,  has  been  studied  by  Wundt  for  sen- 
sations of  sound  occasioned  by  the  fall  of  a  hammer  or  ball — with 
the  following'  result  : 


Height  of  hammer.  Reaction-time. 

Sec. 

1   millimeter 0.217 

4  millimeters 0.146 

8  millimeters 0.132 

16  millimeters 0.135 


Height  of  ball.  Eeaction-time. 

Sec. 

2  centimeters 0. 161 

5  centimeters 0.176 

25  centimeters 0.159 

55  centimeters 0.094 


This  effect  is  obtained,  of  course,  only  within  certain  limits  ;  for 
the  sound  must  not  be  so  loud  as  to  startle  and  confuse.  Thus, 
also,  when  the  length  of  the  electric  spark  which  stimulates  the 
retina  is  increased  the  reaction-time  is  diminished.  Exner "  found 
that,  while  it  was  0.1581-0.1502  sec.  for  sparks  0.5-1  mm.  in  length, 
it  was  0.1479-0.1384  sec.  for  those  2-5  mm.  long,  and  diminished 
to  0.1229  sec.  for  those  of  7  mm. 

The  reaction-time  is  also  diminished  by  indicating  the  instant 
at  about  which  the  sensation  may  be  expected,  through  some  pre- 
ceding signal.  The  interval  for  the  sound  caused  by  a  ball  falling 
25  ctm.,  which  without  signal  was  0.253  sec,  was  reduced  by  a 
signal  to  0.076  sec.  ;  and  when  the  fall  was  5  ctm.  the  interval  was 
reduced  by  the  signal  from  0.266-0.175  sec.°  In  order  to  secure 
this  effect,  however,  the  interval  between  signal  and  impression 
should  be  nearly  constant,  and  not  so  long  as  to  overstrain  atten- 

'  Comp.  von  Kries  and  Auerbach,  Arcliiv  f.  Anat.  u.  Physiol.,  Physiolog. 
Abth. .  1877,  p.  359  f. 

-  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  269  f. 
3 See  Wundt,  Pliysiolog.  Physiol.,  ii.,  p.  238. 


478 


THE   FIXIKG   OF   EEACTION-TIME. 


tion  or  prevent  the  carrying  of  a  definite  mental  image  of  this  in- 
terval. 

The  detailed  investigations  of  Berger,'  recently  published,  an- 
nounce the  following  conclusions :  (1)  The  reaction-time  increases 
in  inverse  ratio  to  the  intensity  of  the  stimulus,  and  so  much  the 
faster  the  nearer  we  approach  the  "  threshold  "  (or  lower  limit)  of 
the  stimulus  ;  (2)  discernment-time  is  related  to  alterations  in  the 
intensity  of  the  stimulus  in  the  same  way  as  simple  reaction-time  ; 
and  (3)  will-time  is  independent  of  the  intensity  of  the  stimulus. 

§  11.  When  the  quality  of  the  impression  to  be  expected  is 
known,  but  its  intensity  is  unknown,  the  reaction-time  is  increased. 
The  increase  is  greater  if  the  alternation  of  intensities  is  very  irreg- 
ular.    This  fact  is  exhibited  by  the  following  table :  ^ 


I.  Uniform  change  of  intensity. 

Sec. 

Loud  sound 0. 116 

Feeble  sound 0.127 


II.  Irregular  change  of  intensity. 

Sec. 

Loud  sound 0.189 

Feeble  sound 0.298 


By  suddenly  intercalating  a  feeble  sound  in  a  series  of  loud  noises 
the  reaction-time  may  be  prolonged  to  0.4  or  0.5  sec.  It  is  also 
greatly  lengthened  when  the  impression  is  wholly  unexpected  by 
the  subject  of  the  experiment  being  taken  off  guard,  as  it  were  ;  in 
such  a  case,  also,  it  may  reach  0.5  sec.  As  might  be  expected,  it 
takes  longer  to  react  in  an  unnatural  and  unaccustomed  way.  It 
requires  more  time  to  react  with  the  foot  than  with  the  hand  ;  a 
mean  reaction-time  from  eye  to  foot  was  found  by  Exner  to  be 
0.1840  sec. 

§  12.  The  reaction-time  for  the  sense  of  taste  varies  in  depend- 
ence upon  the  part  of  the  tongue  to  which  the  stimulus  is  applied, 
and  upon  the  character  of  the  gustable  substance.  It  also  varies 
greatly  with  different  persons.  Von  Wittich  fixed  it  at  0.167  sec. 
from  tongue  to  hand,  by  using  the  sour  taste  which  the  electrical 
current  excites.  The  reaction-time  for  sugar  on  the  tip  of  the 
tongue  varied,  for  three  different  persons,  from  0.1639  to  0.3502 
sec.  ;  and  for  quinine,  for  two  persons,  from  0.2196  to  0.993  sec. 
For  the  root  of  the  tongue,  it  was  found  to  be  0.552  sec.  for  sugar, 
and  0.502  sec.  for  quinine.^  Little  has  been  done  to  determine  the 
reaction-time  of  smell.  Some  have  maintained  that  it  must  be  much 
longer  than  the  reaction-time  of  sight  and  hearing,  and  even  reach 
several  seconds  ;  others  have  held  that,  although  slower  than  these 

»  Wundt's  Philosoph.  Studien,  1885,  III.,  heft  i.,  pp.  38  fE. 
'^  Wundt,  Physiolog.  Psychologie,  ii.,  p.  241  f. 

3  Von  Vintschgau  and  Honigschmied,  in  Pfliiger's  Arcliiv,  x.,  1;  xii.,  2; 
xiv.,  3. 


THE   METHOD    OF  DON'DERS.  479 

senses,  smell  lias  probably  a  reaction-time  of  only  a  fraction  of  a 
second.  The  latter  view  seems  more  recently  to  have  been  con- 
firmed by  the  experiments  of  Moldenhauer/  who  obtained  the  fol- 
lowing among  other  figures  :  Oil  of  mentha,  0.203-0.362  sec.  ;  oil 
of  bergamot,  0.212-0.374  sec.  ;  camphor,  0.226-0.492  sec.  ;  musk, 
0.319  sec.  Taste  and  smell  are  much  more  subject  to  change  in 
the  length  of  the  reaction-time  through  individual  peculiarities 
of  the  exciting  substances  and  of  the  subjects  of  experiment,  than 
are  the  senses  of  hearing,  sight,  and  touch. 

§  13.  Having  obtained  the  mean  reaction-time  for  the  different 
senses  under  varying  circumstances,  the  method  of  investigation 
requires  that  it  should  be  determined  how  much  the  reaction-time 
is  increased  by  increasing  and  complicating  the  psycho-physical 
elements.  One  principal  question  to  be  answered  by  this  method 
is  the  following  :  How  much  time  is  required  for  "  apperception"  ov 
clear  discernment  of  perceived  objects  in  the  central  point  of  con- 
sciousness under  different  conditions  ?  This  question  has  been  veiy 
patiently  and  fully  investigated,  at  first  by  Donders,  and  since  by 
many  observers,  especially  by  von  Kries  and  Auerbach." 

Donders  ^  and  his  pupils  were  the  first  to  examine  in  detail  the 
speed  of  psychical  processes,  with  a  view  to  determine  how  long  it 
takes  to  recognize  one  of  two  or  more  different  presentations  of 
sense  ;  and  also  how  long  to  solve  the  dilemma  of  choosing  one 
of  two  means  for  making  the  reaction.  For  example,  in  one  series 
of  exj)eriments  the  eye  was  suddenly  stimulated  with  either  red  or 
white  light  (the  subject  of  the  experiment  not  knowing  which  to 
expect),  the  signal  for  the  former  to  be  given  with  the  right  hand, 
the  signal  for  the  latter  with  the  left.  In  another  series  of  experi- 
ments, the  quality  of  the  light  or  sound  was  to  be  recognized  before 
reaction,  but  reaction  was  to  take  place  only  in  case  a  particular 
one  of  the  two  sensations  was  recognized  ;  in  case  the  other  sensa- 
tion appeared  in  consciousness,  no  reaction  was  to  take  place.  In 
other  words,  discernment  of  the  presentation  of  sense  was  to  be 
followed  by  the  choice  between  reacting  in  a  prescribed  way  and  re- 
fraining from  reacting  at  all.  In  still  other  experiments  the  stimulus 
consisted  of  a  "vocal  clang  "called  into  a  "phonautograph"  by  one 
person,  and  the  reaction  consisted  of  the  same  clang  repeated  by 
another  person  ;  or,  again,  the  recognition  of  one  or  more  letters 
seen  was  signalled  by  a  movement  of  the  hand.     By  such  methods 

'  Wundt's  Philosoph.  Studien,  I.,  heft  iv.,  p.  606  f. 

2  See  their  article  in  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth.,  1877,  pp. 
297-378. 

3  Archiv  f.  Auat,  Physiol.,  etc.,  1868,  pp.  657-675. 


480  APPEKCEPTION   AND   WILL   TIME. 

Donders  made  the  mean  reaction-time  of  five  persons,  for  dis- 
cernment between  red  and  white  Hght,  with  choice  of  the  hand  by 
which  to  react,  to  be  0.154  sec;  the  minimum,  0.122  sec;  the 
maximum,  0.184.  The  mean  reaction-time  for  two  letters,  with 
discernment  and  signal  by  calUng  them  out,  was  found  to  be  0.166 
sec;  when  the  number  of  letters  was  increased  to  five,  the  mean 
reaction-time  rose  to  0.170.  It  took  0.180  sec.  to  discern  and 
repeat  a  vocal  clang  when  known,  0.268  sec.  when  unknown.  With 
the  method  of  reacting  only  on  one  clang  and  keeping  silent  when 
others  were  heard,  the  mean  I'eaction-time  varied  from  0.201  to 
0.284  sec.  The  investigations  of  Donders  made  obvious  the  fact 
already  stated  (p.  475  f.),  that  the  natural  connection  between  the 
sensation  and  the  peculiar  means  chosen  for  reaction  is  of  in- 
fluence in  detei-mining  the  interval.  Donders  assigned  0.039  sec. 
to  the  psychical  process  of  the  development  of  a  presentation  of 
sound  in  his  own  case,  and  a  little  less  to  the  formation  of  a 
decision  of  will. 

§  14.  Another  and  ingenious  method  of  determining  the  time 
required  for  "  apperception  "  was  proi^osed  by  Baxt ;'  it  was  based 
upon  the  principle  of  the  inei'tia  of  the  senses,  especially  of  sight. 
Suppose  the  question  raised,  How  long  must  an  image  act  on  the 
optical  apparatus  in  order  to  occasion  a  clear  presentation  of  sense  ? 
It  may  be  answered  by  discovering  how  quickly  after  a  given  im- 
pression another  stronger  one  must  follow  in  order  that  the  latter 
may  overtake  the  former,  and  quench  it — as  it  were — before  it 
reaches  the  focus  of  apperception.  Let  then  some  image  which 
requires  discernment  to  interpret  it — as  the  image  of  several  letters, 
or  of  a  simple  geometrical  figure — be  thrown  upon  the  retina,  and 
let  this  image  be  succeeded  after  a  brief  interval  by  the  image  of  a 
bright  white  disk  ;  then,  if  the  interval  be  less  than  a  certain  time, 
apperception  (or  clear  vision,  with  discernment  of  the  significance  of 
the  image)  will  not  take  place  at  all.  Baxt  found  that  the  time  ne- 
cessary under  these  circumstances  for  a  presentation  of  visual  sense 
depends  upon  the  intensity  of  the  second  excitation  ;  it  increases 
as  this  intensity  increases.  It  depends  also  upon  the  complexity  of 
the  apperception  required  ;  to  recognize  three  letters  required  only 
about  half  the  time  necessary  to  recognize  five  or  six.  With  an 
interval  of  0.0048  sec.  between  the  two  excitations,  the  first  ap- 
peared as  scarcely  a  trace  of  a  weak  shimmer  ;  with  an  interval  of 
0.0096  sec,  letters  appeared  in  the  shimmer — one  or  two  of  which 
could  be  partially  recognized  when  the  interval  increased  to  0.0144 
sec.  When  the  interval  was  made  0.0192  sec,  the  objects  were  a 
'  See  Pfliiger's  Archiv,  iv. ,  pp.  325  ff. 


CONCLUSION'S   OF   KRIES   AND   AUERBACH. 


481 


little  more  clearly  discerned;  at  0.0336  sec.  four  letters  could  be 
well  recognized  ;  at  0.04:32  sec,  five  letters  ;  and  at  0.0528  sec.  all 
the  letters  could  be  read. 

§  15.  The  method  of  Baxt  was  rejected  by  von  Kries  and  Auer- 
bach'  as  unsuitable  to  answer  the  question  most  interesting  to 
psycho-physical  researches  ;  because  it  includes  as  an  inextricable 
factor  the  time  used  ujd  in  the  peripheral  nerves.  Besides,  we 
have  no  means  of  estimating  just  to  what  stadium  a  psycho-physi- 
cal process  must  have  advanced  when  it  becomes  impossible  for  a 
strong  succeeding  sensation  to  overwhelm  it.  These  observers  pre- 
ferred, therefore,  the  method  employed  by  Donders,  and  especially 
in  the  form  (called  "  Danders'  G-method  ")  in  which  the  subject  of  ex- 
periment reacts  in  one  prescribed  way  or  else  refrains  from  reacting 
at  all.  By  this  method  they  endeavored  to  answer  the  questions  : 
"  How  long  time  passes  after  the  occurrence  of  a  stimulus  of  sight 
before  I  know  what  color  it  has  ;  and  how  long  before  I  know  at 
what  place  in  the  field  of  sight  I  experience  it,"  etc.  ?  Their  results 
may  be  summed  up  in  the  following  table.^  [The  numbers  give 
the  time  assigned  by  them  to  the  discernment  involved  in  the  va- 
rious processes  performed — that  is,  the  psycho-physical  time  exclu- 
sive of  all  solution  of  a  dilemma  by  the  will.  This  time  is  found 
by  subtracting  the  simple  reaction-time,  or  time  necessary  for  re- 
acting when  no  discernment  is  required,  from  the  whole  time  re- 
quired for  the  process  including  such  discernment.] 


Discernment  of  the  direction  of  light 

Discernment  between  two  colors 

Localization  of  sound  (minimum) 

Discernment  of  tone  when  higher 

Localization  of  sensations  of  touch 

Localization  of  distance  by  sight 

Discernment  between  tone  and  noise 

Judgment  of  intensity  of  sensations  of  touch  (strong) 

Discernment  of  tone  when  lower 

Judgment  of  intensity  of  sensations  of  touch  (weak). 
Localization  of  sound  (maximum) 


Auerbach. 

Von  Kries. 

Sec. 

Sec. 

0.011 

0.017 

0.012 

0  034 

0.015 

0.032 

0.019 

0.049 

0  021 

0.036 

0.022 

0.030 

0.022 

0.046 

0.023 

0.061 

0.034 

0.054 

0.053 

0.105 

0.062 

0.077 

§  16.  Various  interesting  discoveries  were  made  during  the  course 
of  the  experiments  which  resulted  in  preparing  the  foi-egoing  table. 
For  example,  it  was  found  that  the  simple  reaction-time  for  A. 
(Auerbach),  when  stimulus  was  applied  to  the  middle  finger  or 

1  See  Archiv  f.  Anat.  u.  Physiol.,  1877,  Physiolog.  Abth.,  p.  298. 
5  Ibid. ,  p.  346  f . 
31 


482  APPERCEPTIOlSr   AND   WILL   TIME. 

back  of  tlie  hand,  was  0.146-0.147  sec;  and  for  K  (Kries\ 
0.117-0.119  sec.  But,  as  the  table  shows,  when  discerament  wag 
required  of  the  two  observers,  the  reaction-time  of  K.  was  relative- 
ly so  much  increased  as  to  make  his  discernment-time  greater  than 
that  of  A.  The  result  of  practice  in  discernment  was  found  to  hold 
good  for  other  areas  of  the  skin  than  those  in  experimenting  upon 
which  the  practice  was  gained.  For  discernment  among  three 
places  (middle  finger,  back  of  hand,  and  middle  of  lower  arm),  the 
order  being  unknown  and  only  one  to  be  reacted  on — the  mean  in- 
terval required  was  for  A.  0.028  sec,  and  for  K.  0.050  sec.  ;  fur- 
ther practice,  however,  reduced  this  interval  to  about  the  same  as 
that  required  for  two  places. 

Discernment  between  two  intensities  of  the  sensation  of  touch  was 
found  to  be  very  uncertain  and  difficult.  Many  more  false  reactions 
followed  the  attempt  to  tell  whether  the  dorsal  side  of  the  last  of 
the  phalanges  of  the  middle  finger  was  being  hit  with  the  weaker 
or  the  stronger  of  two  stimuli  than  occurred  in  the  attempts  to 
localize  tactile  sensations.  The  discernment-time,  when  reaction 
followed  the  stronger  stimulus,  was  0.016-0.034  sec.  for  A,  and 
0.05-0.07  for  K. ;  when  reaction  followed  the  weaker  stimulus,  the 
discernment-time  was  0.035-0.069  sec.  for  A,  and  0.089-0.114  forK. 
The  character  of  our  judgments  of  intensity  is,  perhaps,  dependent 
on  the  steepness,  as  it  were,  with  which  the  curve  rises  in  consci- 
ousness ;  but,  however  this  may  be,  it  appears  that  we  discern  how 
and  where  we  are  affected  with  a  sensation  more  promptly  than 
about  how  much  we  are  affected. 

When  discernment  between  two  simple  tones  of  different  pitch  is 
required,  the  reaction  follows  the  one  of  higher  pitch  more  promptly. 
Thus  the  discernment-time,  under  such  circumstances,  was  for  A, 
0.015-0.044  sec,  and  for  K,  0,043-0,11 ;  but,  if  reaction  followed 
the  tone  of  lower  pitch,  the  discernment-time  for  A,  was  0.03-0.059 
sec,  and  for  K,  0.045-0,092.  To  discern  tone  from  noise,  when  re- 
action followed  the  tone,  A.  required  0.015-0.023  sec,  and  K  0.036 
-0.055  ;  when  reaction  followed  the  noise,  A's  discernment-time  was 
0.017-0.025  sec,  and  K's,  0.045-0,047.  The  reaction-time  dimin- 
ishes as  the  pitch  rises  ;  for  very  high  notes  it  nearly  reaches  the 
limit  required  for  hearing  the  noise  of  the  electric  spark.  The  ex- 
planation for  these  experiences  requires  reference  again  to  the  fact 
that  some  15-20  vibrations  are  necessary  to  start  the  organ  so  that 
the  sensation  of  musical  tone  can  be  received  at  all. 

The  simple  reaction-time  for  sensations  of  sound  remains  nearly 
the  same  for  all  changes  in  the  angle  by  which  the  locality  of  the 
sound  diverges  from  the  median  plane  between  the  two  ears.     But 


THE   EXPERIMENTS   OF   WUNDT. 


483 


the  time  required  for  discerning  the  locality  of  the  sound  varies 
greatly  for  the  different  sizes  of  this  angle.  Thus  the  discernment- 
time  for  locality,  as  to  right  or  left,  varied  for  Auerbach  and  Kries 
as  follows : 


Angle  ISC-SS". 

Angle  35°-2G<'. 

Angle  26°-ll». 

A 

Sec. 
0.020 
0.013 

Sec. 

0.033 

0.122 

Sec. 

0  120 

K 

0  153 

The  discernment-time  required  for  localizing  the  direction  of  a 
spark  by  direct  vision  varied  for  A.  from  0.005  to  0.025  sec,  and  for 
K.  from  0.006  to  0.029  sec.  ;  by  indirect  vision,  for  A.  from  0.008 
to  0.028  sec,  and  for  K  from  0.007  to  0.028  sec  For  locaUzing 
distance,  A.  required  0.019  to  0.027  sec.  of  discernment-time,  when 
the  object  arose  in  front  of  the  fixation-point,  and  K.  0.027  to  0.035 
sec  ;  but  A.  required  0.019  to  0.029  sec,  and  K.  0.021  to  0.036  sec, 
when  the  object  arose  behind  this  point. 

§  17,  Various  strong  objections  have  been  raised  to  the  validity 
of  the  results  reached  by  the  observers  last  mentioned.  For  ex- 
ample, Richet'  thinks  that  an  interval  so  small  as  their  "  discern- 
ment-time" (about  0.03  sec.)  is  below  the  limit  of  the  experimental 
error.  But  the  constancy  of  the  results  obtained  by  such  a  large 
number  of  experiments  with  reference  to  the  mental  peculiarities 
of  the  two  subjects  of  experiment,  and  to  the  different  kinds  of  men- 
tal processes  involved  (discernment  of  locality,  quaUty,  quantity, 
etc.),  is  too  great  to  allow  of  the  results  being  summarily  rejected. 
The  criticism  of  "Wundt  ^  as  applied  to  the  method  employed  (the 
so-called  "Bonders'  C-method")  is  much  more  pertinent.  This 
veteran  experimenter  considers  that  the  psycho-physical  time  re- 
quired to  discriminate  between  two  or  more  possible  presentations 
of  sense,  and  then  react  only  in  case  one  of  them  is  apperceived, 
cannot  all  be  allotted  to  discernment-time.  For  an  element  of  vo- 
lition, or  will -time,  is  as  truly  involved  in  the  decision  whether  to  react 
or  not  to  react  as  in  the  decision  between  two  modes  of  reaction. 

With  a  view,  then,  to  analj'ze  these  elements  more  perfectly,  and 
so  determine  the  exact  duration  of  "apperception,"  in  the  sense 
in  which  the  word  is  used  by  Wundt,  another  method  of  experiment 
has  been  employed  by  Friedrich.^  In  this  method  the  subject  of 
experiment  is  warned  ichen  to  expect  one  of  two  or  more  colors 

'  See  Revue  philosophique,  VI.,  p.  395. 

^  Physiolog.  Psycliologie,  ii. ,  p.  251  f. 

3  See  Wundt's  Philosoph.  Studien,  II.,  heft  i.,  pp.  39  S. 


484 


APPERCEPTION   AND   WILL   TIME. 


to  be  discerned,  but  does  not  know  which  one  to  expect ;  only  one 
way  of  reaction  is  employed  for  all  cases ;  and  the  judgment  of  the 
subject  is  left  to  determine  just  when  he  clearly  discerns,  or  "  apper- 
ceives,"  the  object.  The  time  of  apperception  is  then  found  by  sub- 
tracting the  simple  reaction-time  (or  time  necessary  to  announce  the 
sensation  without  discernment)  from  the  entu'e  reaction-time  thus 
obtained.  In  this  way  the  interval  for  apperception  was  fixed  at 
0.030  to  0.185  sec.  for  white,  in  the  case  of  Wundt,  and  0.044  to 
0.146  for  black  ;  in  the  case  of  Tischer,  0.046  to  0.112  sec.  for  white, 
and  0.021  to  0.061  for  black  ;  and  in  the  case  of  Friedrich  himself, 
0.042  to  0.084  sec.  for  white,  and  0.019  to  0.064  for  black.  The  mean 
duration  o:^  apperception,  as  derived  from  all  the  experiments  with 
two  color-sensations,  was  0.086  sec.  for  W.,  0.047  for  T.,  0.050  for  F. 
§  18.  The  time  required  for  discernment  increases,  of  course, 
when  the  other  conditions  are  kept  as  nearly  as  possible  the  same, 
but  the  number  of  objects  is  increased  among  which  the  discern- 
ment is  required.  For  example,  Friedi'ich  found  that  when  four 
(instead  of  two)  colors — black,  white,  green,  and  red — were  inter- 
changed in  an  unknown  order,  both  the  reaction-time  as  a  whole 
and  the  duration  of  apperception  were  increased.  The  latter  for 
black  as  one  of  four  colors  was,  when  averaged  for  several  series  of 
experiments,  0.081  to  0.141  in  Wundt's  case,  0.021  to  0.105  in  Tisch- 
er's,  0.076  to  0.197  in  his  own.  With  red  as  one  of  four  colors  the 
duration  of  apperception  was  0.049  to  0.247  for  W.,  0.024  to  0.124  for 
T.,  and  0.066  to  0.234  for  F.  Experiments  were  also  instituted  with 
a  view  to  determine  how  long  it  takes  to  discern  composite  percep- 
tions of  sight.'  For  this  purpose  printed  figures  of  6  mm.  high 
and  3.8  mm.  broad  were  employed,  ranging  from  one  to  six  places — 
the  reaction  being  in  the  form  of  calling  the  number  constituted  by 
the  figures  as  arranged  when  displayed.  The  mean  time  required 
for  apperception  by  the  three  subjects  of  experiment  is  shown  by 
the  following  table  :  [The  figures  at  the  head  of  the  columns  indi- 
cate the  number  of  places  which  the  numbers  had  in  the  different 
series  of  experiments  ;  the  letters,  the  subjects  of  experiment  ;  the 
figures  under  the  head,  the  seconds  of  apperception-time.] 


1. 

2. 

3. 

4. 

5. 

6. 

w 

Sec. 

0.344 
0.290 
0.820 

Sec. 
0.361 
0.380 
0.346 

Sec. 

0.354 
0.493 
0.344 

Sec. 

0.459 
0.709 
0.481 

Sec. 

0.573 
0.849 
0.670 

Sec. 

0.817 

T 

1.197 

F 

1.043 

'  Wuudt's  Philosopli.  Studieu,  I.,  lieft  i. ,  p.  53  f. 


THE    HEADING    OF   NUMBEilS.  485 

It  will  be  noticed  that  the  reaction  time  for  numbers  of  three 
places  is  not  much  greater  than  that  for  numbers  of  one  place ;  but 
when  the  complexity  is  increased  to  four  places,  the  reaction-time 
is  suddenly  and  largely  increased.  This  fact  is  probably  due  in 
part  to  the  habit  of  grasping  numbers  mentally  in  periods  of  three 
places  each.  It  is  not  certain,  however,  that  the  apperception-time 
as  calculated  by  this  method  is  trustworthy  ;  for,  although  the  sub- 
ject of  experiment  reacts,  and  then  notifies  the  number  discerned, 
the  act  of  discernment  may  really  be  completed  after  the  reaction 
has  taken  place.  Moreover,  a  certain  time  for  accommodating  the 
eye  must  be  allowed  ;  especially  in  the  case  of  numbers  of  five  or 
six  figures  each.  This  time,  in  the  opinion  of  one  critic,  may  be 
placed  at  0.166  to  0.186  sec.  A  more  recent  investigator^  concludes 
that  the  true  discernment-time  in  a  composite  perception  is  possibly 
so  short  as  to  occupy  only  a  few  hundredths  of  a  second.  For 
numbers  of  one  to  three  places  the  interval  between  perception  and 
apperception  is  0.015  to  0.035  sec.  This  conclusion  accords  with 
and  enforces  that  arrived  at  by  the  careful  experiments  of  von  Kries 
and  Auerbach. 

Cattell  ° — by  assuming  that  perception-time  and  will-time  are 
about  equal,  and  thus  dividing  into  two  parts  the  remainder  ob- 
tained by  subtracting  the  simple  reaction-time  from  the  whole  time 
including  both  discernment  and  choice — estimated  the  perception- 
time  for  light,  of  B.  at  0.030  sec,  and  of  himself  at  0.050.  It  took 
longer,  of  course,  to  discern  between  two  colors.  Between  red  and 
blue  discernment  required  about  0.038  sec.  for  B.,  and  0.054  for  C. 
If  one  color  among  ten  was  to  be  discerned,  the  time  rose  to  0. 105 
for  B.,  and  0.117  for  C.  The  time  required  to  discern  one  letter 
from  all  the  others  was  found  to  vary  somewhat  for  the  different 
letters  ;  but  the  legibility,  or  comparative  accuracy  of  the  quick 
discernment,  varied  still  more.  In  this  sense  the  letter  W  is  about 
four  times  as  "  legible  "  as  E.  The  discernment-time  for  a  simple 
picture  of  a  familiar  object  was  found  to  be  about  the  same  as  that 
for  a  color,  and  shorter  than  that  for  a  letter  or  a  word. 

§  19.  We  have  already  seen  (p.  480)  that  Donders  assigned  a 
little  less  time  (0.036  sec.)  to  the  operation  of  will  in  setting  free 
the  required  impulse  when  a  dilemma  was  presented  to  it  than  is 
required  for  discernment  between  two  objects  of  the  visual  sense. 
The  duration  of  "  ivill-time"  (the  third  element  of  psycho-physical 
time)  has  since  been  investigated  at  greater  length  by  Friedrich. 
Buccola,    Merkel,  and   others.     The  first  of   these   experimenters 

1  Tigerstedt,  in  Zeitsclirift  f.  Biologie,  1883,  XIX.,  p.  43  f. 

2  See  Mind,  July,  1886. 


4SG  APPEllCEPTION   AND    WILL   TIME. 

determiued  the  time  required  for  simple  choice  by  finding  how 
much  the  reaction-time  is  increased  when  the  subject  of  experiment 
must  decide  whether  to  react  or  not. '  For  example,  let  the  sensa- 
tions of  black  and  white  follow  each  other  in  unknown  order,  it  be- 
ing understood  that  only  white  is  to  be  followed  by  reaction.  The 
interval  for  simple  choice  was  thus  found  by  Friedrich  to  have  a 
mean  value  of  0.152  sec.  for  W.,  0.184  for  T.,  and  0.183  for  him- 
self ;  it  lay,  therefore,  between  \  and  \  sec.  If  choice  was  re- 
quired, however,  between  the  two  hands — reaction  with  one  hand 
being  the  sequence  of  the  appearance  of  one  color,  and  with  the 
other  hand  of  the  appearance  of  the  other  color — the  interval 
assigned  to  this  element  of  psycho-physical  time  increased  to  0.188 
sec.  for  W.,  0.330  for  T.,  and  0.287  for  F.^ 

Merkel '  has  perhaps  investigated  most  thoroughly  the  time- 
relations  of  activities  of  the  Avill.  The  question  he  proposes  for 
answer  is  the  following :  How  long  does  it  take,  under  different 
circumstances,  to  set  free  a  voluntary  impulse?  He  assumes  that, 
in  all  cases  where  reaction  follows  disceinment  between  two  or 
more  impressions,  some  "will-time"  is  present,  although  the 
amount  of  this  time  may  become  so  minute  as  to  escape  detection. 
The  method  of  Merkel  was  suggested  by  Wundt.  The  simple 
reaction-time  (E),  or  time  requii'ed  when  the  nature  of  the  stimulus 
is  known  and  the  mode  of  reaction  fixed  the  same  for  all  cases,  is 
first  found.  The  reaction-time  x*equired  to  discern  clearly  one  of 
two  or  more  impressions,  and  announce  the  fact  in  some  one  way 
previously  determined  upon  (R  d),  is  next  found.  Finally,  the  I'e- 
action-time  is  found  for  cases  where  there  is  involved,  in  addition 
to  discernment,  a  choice  between  one  or  more  ways  of  reacting,  or 
between  reacting  and  not  reacting  [R  d  w).  The  difference  lid— li  is 
then  held  to  give  the  "  discernment-time ; "  the  difference  II  d  iv — li  d 
is  held  to  give  the  "  will-time."  It  is  with  the  latter  that  we  are 
now  concerned.  For  his  experiments  Merkel  used  figui'es  of  about 
13  mm.  altitude  placed  250  mm.  distant  from  the  eye.  To  deter- 
mine the  reaction-time,  including  discernment  (R  d),  but  not  includ- 
ing choice,  reaction  is  ordered  invariably  with  the  same  finger.  To 
determine  reaction-time,  including  choice  {R  d  ?o),  reaction  is  ordered 
with  some  one  finger  of  either  hand  previously  assigned  to  each 
number.  Will-time  is  then  found  by  subtracting  the  reaction- 
time  in  the  former  case  from  that  in  tbe  latter  (R  dio—JR  d).     The 

'  Friedrich,  in  Wundt's  Philosoph.  Studien,  I.,  heft  1. ,  p.  57  f. 
'^  Only  a  few  experiments  of  this  kind   were  tried ;  the  numhers  are  those 
given  by  Merkel  in  his  article. 

^  Article  in  Wundt's  Philosoph.  Studien,  II.,  heft  i. ,  pp.  73-127. 


DIFFEREXGES    OF   INDIVIDUALS.  487 

results  showed  that  ^vhile  the  simple  reaction-time  for  the  different 
fingers  of  both  hands  does  not  differ  gi'eatly,  the  difference  in  will- 
time  for  the  different  fingers  is  much  more  marked.  The  latter 
difterence  is  greater  among  the  fingers  of  the  right  than  of  the  left 
hand.  For  ten  persons  experimented  upon,  the  mean  inteiTal 
required  for  setting  free  a  definite  reaction,  ^vith  a  choice  between 
two  possible  courses,  varied  from  0.02-t  to  0.155  sec.  This  inter- 
val increases  for  every  additional  course  possible  until,  in  case  the 
subject  of  the  experiment  is  required  to  select  one  of  his  ten  fingers 
with  which  to  react  on  receiving  an  impression  corresponding  to 
that  fiDger,  the  will-time  becomes  0.298  to  0.448  sec. 

Yery  interesting  individual  differences  in  the  speed  of  decision 
attained  under  different  conditions  of  complexity  are  brought  out 
by  Merkel's  experiments.  This  fact  may  be  shown  by  plotting  the 
curve  of  the  will-time  of  each  individual.  In  general,  it  was  found 
that  the  individual  differences  increased  as  the  complexity  of  the 
choice  required  was  increased  from  one  to  five  places,  and  that  they 
then  fell  off",  being  least  at  nine  or  ten  places.  That  is  to  say,  different 
individuals  differ  much  more  markedly  in  the  speed  with  which  they 
can  choose  one  of  two  or  five  than  one  of  nine  or  ten  different  pos- 
sible ways  of  reaction.  Merkel's  value  for  will-time  when  the  choice 
lies  between  two  courses  [R  2r=0.024:  to  0.155  sec.)  may  profitably  be 
compared  with  that  given  by  Buccola  for  choice  between  motion  and 
rest  with  discernment  of  color-tone  and  locality  (0.028  sec.  and  0.066 
see.  respectively),  or  Avith  that  given  by  Tischer  '  for  choice  between 
motion  and  rest  (for  nine  persons,  0.052  to  0.179  sec.)  or  for  choice 
between  two  symmetrical  motions  (0.033  to  0.179  sec). 

§  20.  A  careful  survey  of  the  statistics  and  discussions  furnished 
by  different  exj)erimenters  shows  that  it  is  not  as  yet  possible  to 
analyze  with  perfect  confidence  the  different  elements  of  psycho- 
physical time.  Wundt  seems  justified  in  holding  that  will-tin:e  is 
necessarily  involved  in  the  choice  between  motion  and  rest.  But, 
on  the  other  hand,  von  Kries  and  Auerbach  appear  to  have  reduced 
this  time  almost  or  quite  to  zero,  by  practice  and  by  arranging 
their  experiments  under  the  most  favorable  conditions.  By  elimi- 
nating will-time  they  have,  perhaps,  found  about  what  is  the  least 
possible  interval  required  for  simjDle  acts  of  discernment.  There  is 
other  evidence  (fi'om  the  phenomena  of  rhythm,  etc.),  however,  to 
indicate  that  successive  acts  of  discernment  may  attain  a  higher 
rate  of  speed  than  is  possible  for  successive  acts  of  will. 

§  21.  Investigation  has  also  been  dii'ected  toward  determining 
how  far  series  of  events  in  consciousness  correspond,  as  regai'ds 
'  See  Wuudt's  Pliilosopli.  Studien,  I.,  heft  iv. ,  p.  533  f. 


488  APPEECEPTIOlSr   AND   WILL   TIME. 

time,  to  the  series  of  excitations  which  occasion  them.  Something 
may  thus  be  accomphshed  toward  fixing  the  time-rate  of  conscious- 
ness, as  well  as  the  interval  which  it  is  possible  for  the  mind  to  ap- 
preciate with  the  nearest  approach  to  perfect  accuracy.  In  all  the 
preceding  experiments  the  subject  of  them  is  uniformly  aware  that 
a  pause,  as  it  were,  takes  place  between  the  excitation  and  the  re- 
action ;  this  pause  he  is  able  to  estimate  with  much  accuracy,  and 
so  to  tell  whether  his  effort  to  react  promptly  has  been  more  or  less 
successful.  Exner '  states  that  in  39  cases  of  reaction  from  eye  to 
foot,  which  had  a  mean  of  0.184  sec,  the  reaction  was  always  felt 
(with  a  single  exception)  to  be  "  too  slow  "  when  it  reached  0.1994 
sec,  and  pronounced  "  very  good  "  when  it  fell  below  0.1781  sec; 
its  time  was  therefore  estimated  Avithin  about  0.01  sec.  There  is 
abundant  proof,  however,  that  the  speed  and  duration  of  our  sensa- 
tions, as  estimated  in  consciousness,  do  not  precisely  correspond 
with  the  series  of  stimulations  of  the  organ  of  sense.  Indeed, 
under  certain  circumstances  very  remarkable  errors  may  occur  in 
our  estimate  of  both  the  rate  and  the  interval  of  our  mental  acts. 

To  show  the  fact  and  amount  of  the  error  which  takes  place  when 
we  are  called  to  intercalate  an  excitation  of  any  kind  in  a  series  of 
impressions,  Wundt  *  devised  the  following  exj)eriment :  An  indi- 
cator is  kept  moving  at  a  uniform  rate  over  a  graduated  scale,  and 
so  situated  that  the  place  of  the  needle  can  be  clearly  seen  at  each 
instant  of  time.  The  action  of  the  same  clock  which  moves  the 
needle  causes  a  sound  at  any  moment,  but  in  such  a  way  that  the 
subject  of  experiment  does  not  know  when  to  expect  it.  With 
what  position  of  the  needle,  now,  will  the  sensation  of  sound  be 
combined?  Will  the  sound  be  heard  exactly  when  it  occurs  as 
indicated  by  the  needle;  or  later  than  its  real  time  ("  positive  " 
lengthening)  ;  or  earlier  than  its  real  time  ("  negative  "  lengthen- 
ing) ?  The  result  shows  that  one  rarely  hears  the  sound  without 
either  positive  or  negative  displacement  of  it ;  but  most  frequently 
the  lengthening  is  negative — that  is,  one  believes  one  hears  the 
sound  before  it  really  occurs  as  measured  by  the  indicator. 

§  22.  Vierordt,^  after  experimenting  upon  our  power  to  repro- 
duce the  interval  as  heard  between  two  sensations  of  noise,  con- 
cluded that  very  small  intervals  are  regularly  overestimated  and 
greater  ones  underestimated.  The  minimum  of  error  in  estimating 
intervals — the  duration  that  corresponds  most  perfectly  in  our  con- 
sciousness to  the  real  duration  as  measured  by  objective  methods 

!  Hermann's Handb.  d.  Physiol.,  II.,  ii.,  p.  273  f. 
^  Physiolog.  Psychologie,  ii.,  p.  264  f. 
^  Der  Zeitsinn.     Tiibiugen,  1868. 


INTERVAL   OF   MINIMUM   ERROE.  489 

— he  placed  at  1-1.5  sec.  More  recently  (1881)  KoUert '  published 
the  results  of  experiments  instituted  with  a  view  to  determine  the 
accuracy  of  our  sense  of  time.  Suppose  that  one  metronome  is 
marking  off  time,  by  the  sound  it  makes,  with  a  normal  interval 
=  t.  Another  metronome  is  at  the  same  time  at  work  with  an  in- 
terval =  S,  that  may  be  made  to  vary  with  different  experiments, 
and  that  is  set  as  either  equal  to  or  sUghtly  greater  or  less  than  t. 
Let  T  =  the  time  in  our  consciousness  which  is  equivalent  to  t,  and 
A  —  a  constant  representing  the  mean  error  which  is  made  in  es- 
timating the  relations  of  the  two  intervals  (t  and  3) ;  that  is,  A  = 
t  —  ^.  Let  3^  =  the  intervals  of  consciousness  just  observably 
smaller,  and  3^  =  those  just  observably  greater,  than  the  normal 
time  (t).  Then  the  following  table  shows  how  A  varies  as  t  varies; 
dj  giving  the  experiments  in  which  the  interval  of  the  variable 
metronome  was  smaller,  and  d^  those  in  which  it  was  greater,  than 
t  (^^  -  t  =  d,,  and  »,  -  t  =  dj. 


t= 

d,= 

d,= 

A= 

0.4 

-0.018 

+0.090 

+0.036 

0.5 

0.044 

0.098 

0.026 

0.7 

0.044  • 

0.055 

0.005 

0.8 

0.073 

0.060 

-0.006 

1.0 

0.107 

0.063 

0.022 

1.2 

0.206 

0.074 

0.066 

It  will  be  noticed  that,  according  to  these  results,  our  sensitive- 
ness to  minute  differences  of  time  varies  for  different  intervals  so 
that  it  is  greatest  at  0.7-0.8  sec.  (A  =  o  at  about  0.755  sec.) ;  while 
it  falls  off  quickly  for  intervals  less  than  this,  and  more  slowly  for 
intervals  longer  than  this.  Kollert  confirms  Vierordt's  statement 
that  times  above  this  most  favorable  time  are  estimated  too  small, 
and  those  below  too  large.  He  also  concludes  that,  as  the  normal 
time  increases,  our  sensitiveness  to  minute  differences  of  diminution 
is  lessened,  while  our  sensitiveness  to  minute  differences  of  increase 
grows  greater. 

The  same  method  as  that  employed  by  Kollert  has  been  applied 
by  another  observer  ^  to  intervals  longer  than  0.4-1.5  sec.  Using 
intervals  of  1.8-8.0  sec.  for  the  normal  time,  the  sensitiveness  of 
our  estimate  of  minute  differences  was  still  found  to  diminish  as 
the  normal  time  increases ;  thus  the  mean  error  of  all  the  individ- 
uals engaged  in  the  experiments  (A  m)  increased  from  0.0792- 
0.0879  sec.  for  intervals  of  1.8-2.0  sec.  to  0.5988  sec.  for  intervals 

'  Wundt's  Philosoph.  Studien,  I.,  heft  i,  pp.  78  ff. 

«  Estel,  iu  Wundt's  Philosopli.  Studien,  II.,  heft  i.,  pp.  37  ff. 


490  COMPLEX   EEACTIOE"   TIME. 

of  8.0  sec.''  Estel  reaches  the  conclusion  that  "our  ideas  of  time, 
like  our  other  sensations  and  ideas,  are  essentially  conditioned  upon 
past  impressions  belonging  to  the  same  domain  of  sense  ;  and  a 
short  time  makes  the  one  next  succeeding  appear  longer,  while  a 
long  time  shortens  still  more  the  succeeding  shorter  time."  A 
more  recent  investigator  ^  places  the  interval  which  can  be  repro- 
duced with  greatest  accuracy  at  0.53-0.87  sec. ;  but  reaches  the 
conclusion  that,  with  all  other  intervals,  an  error  is  made  which  is 
plus  for  those  above,  and  minus  for  those  below,  this  so-called  in- 
difference-point. This  conclusion  would  seem  to  need  re-examina- 
tion, since  it  is  exactly  the  opposite  of  that  of  preceding  investi- 
gators. The  difference  in  result  may,  however,  be  due  to  difference 
in  the  method  of  experiment,  which  in  the  one  case  consisted  in 
noticing  the  least  observable  difference  in  two  series  of  intervals, 
and  in  the  other  consisted  in  catching,  mentally,  a  given  interval, 
retaining  and  reproducing  it. 

§  23.  In  this  connection  should  be  mentioned  the  results  of  in- 
teresting "  studies  of  rhythm  "  undertaken  by  G.  Stanley  Hall  and 
J.  Jastrow.^  These  observers  experimented  to  find  the  degree  of 
accuracy  with  which  successive  clicks  having  a  constant  interval 
can  be  counted.  It  was  found  that  persons  most  successful  were 
able  to  count  2-4  clicks  with  perfect  accuracy,  when  the  interval  be- 
tween them  was  0.0895  sec;  but  if  this  interval  was  diminished  to 
0.0523  sec,  they  could  not  be  sure  of  more  than  two  clicks.  When 
the  number  of  clicks  was  increased  to  45,  with  the  longer  of  these 
intervals,  the  most  successful  estimates  were  42  and  43  ;  with  the 
shorter  interval,  for  the  same  actual  number,  the  best  estimate  was 
32  and  the  worst  was  17.  The  conclusion  is  thus  reached  that  "  count- 
ing requires  a  series  of  innervations,  if  not  of  actual  muscular 
contractions,"  and  that  "  attention  discriminates  sensation  much 
more  rapidly  than  the  will  can  generate  impulses."  If,  then,  the 
interval  between  the  acoustic  sensations  is  less  than  the  reduced 
reaction-interval  (or  time  necessary  for  starting  successive  impulses 
of  innervation)  between  ear  and  tongue,  some  of  the  sensations  will 
drop  out  of  consciousness  as  a  result  of  the  blending,  as  it  were, 
of  the  later  afferent  with  the  earlier  efferent  stage  of  the  complex 
process.  The  time-sense  for  series  of  mental  phenomena  is  then 
different  for  different  classes  of  these  phenomena.  The  rate  of 
sensation  may  considerably  surpass  the  rate  of  motor  impulses  ; 
"  we  do  not  realize  how  far  the  fastest  counting  falls  short  of  the 

1  Estel,  in  Wundt's  Philosoph.  Studien,  II.,  heft  i.,  p.  43. 
«  L.  T.  Stevens,  in  Mind,  October,  1886,  pp.  393-408. 

2  Mind,  January,  1880,  pp.  55  fE. 


eeproductiojST  of  compositp:  images.  491 

fastest  hearing."  The  same  observers  found  that  the  most  rapid 
possible  rate  of  pronouncing  the  names  of  letters  was  gi'eater  than 
that  of  counting  them  ;  the  former  being  0.248  sec.  per  letter  for 
50  letters,  and  the  latter  0.283  sec.  The  reasons  for  this  dif- 
ference are  apparently  to  be  found  in  the  fact  that  counting  in- 
volves a  severer  sti-ain  on  the  attention  and  more  complex  processes 
of  association  and  discernment  in  order  to  give  to  each  number  its 
right  name  and  place  in  a  series  of  numbers. 

§  24.  We  are  thus  led  to  consider  certain  researches  for  deter- 
mining the  reaction-time  of  yet  more  complex  mental  processes, 
such  as  involve  reproduction  of  composite  images  of  memory  and 
the  association  of  ideas.  The  mean  duration  of  association — that 
is,  "  of  the  time  which  is  required  for  the  reproduction  of  an  image 
of  memory  by  some  apperceived  presentation  of  sense  " — has  been 
investigated  at  great  length  by  Trautscholdt  ^  under  the  direction 
of  Wundt.  For  purposes  of  experiment  the  following  elaborate 
classification  of  the  possible  kinds  of  association  was  adopted.  All 
associations  are  either  (I.)  External  or  indirect,  or  else  (11.)  Inter- 
nal or  direct.  The  former  are  such  as  are  induced  by  the  habit 
of  perceiving  objects  together— simultaneously  or  successively — in 
space  or  time,  without  any  interior  relation  between  them  ;  the 
latter  are  such  as  imply  kinship  in  common  properties  or  other  in- 
herent relations.  External  associations  may,  then,  be  either  simul- 
taneous, as  in  the  case  of  the  parts  of  a  single  presentation  of  sense 
or  of  the  coexistence  of  independent  presentations  ;  or  they  may  be 
successive,  as  in  the  case  of  repeated  impressions  of  sound,  of  sight, 
and  of  the  other  senses.  Internal  associations  may  either  be  such 
as  involve  the  relation  of  ranking  one  mental  object  below  or  above 
another  in  terms  of  genus  and  species  ;  or  they  may  follow  relations 
of  co-ordination,  as  similar  or  contrasted  ;  or  they  may  follow  rela- 
tions of  dependence,  as  of  cause  and  effect,  means  and  end.  To  de- 
termine the  time  required  for  a  "  word-reaction  "  ( Wr),  the  experi- 
menter spoke  aloud  some  word  at  the  instant  that  he  pressed  down 
his  key  ;  and  the  person  reacting  indicated  the  instant  at  which  he 
apprehended  the  word.  The  time  required  for  such  reaction  was 
found  to  have  the  following  mean  value  for  the  four  persons  ex- 
perimented upon  :  For  W.,  0.303  sec;  for  B.,  0.285  ;  for  H.,  0  280  ; 
and  for  T.,  0.173.^  The  time  required  for  the  discernment  of  a  single 
word  is  obtained  by  subtracting  from  these  numbers  the  simple 
reaction-time  {R)  for  each  individual  {Wr—R).     The  result  obtained 

^  Experimentelle  Untersuchungen  iiber  d.  Association  d.  Vorstellungen,  in 
Wundt's  Philosoph.  Studien,  I.,  heft  ii..  pp.  213-250. 
■^  Philosopli.  Studien,  I.,  heft  ii. ,  p.  236. 


492 


COMPLEX   REACTION-TIME. 


gave,  for  W.,  a  "discernment-time"  of  0. 107  sec; for B.,  of  0.177;  for 
H.,  of  0,137 ;  and  for  T.,  of  0.057.  In  experiments  to  determine  the 
duration  of  association,  the  person  reacting  does  not  pi-ess  his  key 
until  the  instant  when  the  reproduction  of  some  idea  called  forth 
by  liearing  the  word  spoken  has  fully  taken  place.  For  example, 
on  hearing  the  word  "zero"  the  idea  of  "infinity"  may  arise  in 
the  mind  ;  or  "market-place"  as  associated  with  "market/'  "port- 
folio "  with  "  letter,"  etc.  The  mean  reaction-time  for  such  as- 
sociation, both  before  and  after  subtracting  the  time  for  word- 
reaction  alone,  was  as  follows  : 


Association-reaction  (Ar). . . 
Association- time  {Ar—  Wr). . 


W. 


Sec. 

1.009 
0.706 


Sec. 
1.037 
0.753 


H. 


Sec. 

1.154 
0.874 


Sec. 

0.896 
0.723 


The  mean  duration  of  association  for  all  the  subjects  of  experi- 
ment (excluding  one  for  special  reasons)  is,  therefore,  placed  at 
0.727  sec.  It  takes,  that  is  to  say,  about  f  of  a  second  of  psycho- 
physical time  to  recall  a  familiar  idea  associated  with  a  word  we 
hear.  This  association-time  was  most  prolonged  in  certain  cases 
where  the  result  may  be  looked  upon  as  odd  and  unexpected,  or 
where  a  pause  would  seem  to  have  taken  place  through  hesitation 
between  several  ideas  simultaneously  suggested.  For  example,  the 
association-time  which  elapsed  between  the  word  "pious"  and  the 
idea  "  God-fearing  "  was  1.132  sec;  between  "  throne  "  and  "  king," 
1.437  ;  between  the  German  word  "  Sieg  "  and  "  a  person  of  this 
name,"  1.626  ;  between  "Karl  "and  "August,"  1.662.  The  mini- 
mum of  association-time  was  reached  with  ordinary  words  where 
the  associated  ideas  were  such  as  all  individuals  are  likely  to  have  in 
common.  Thus,  from  "  gold  "  to  "  silver"  required  only  0.402  sec; 
from  "storm"  to  "wind,"  0.368  ;  from  "clear"  to  "dark,"  0.507; 
from  "north"to  "south,"  0.502;  from"duty"to  "right,"  0.415;  etc 

§  25.  Trautscholdt '  also  found — as  we  should  expect — that 
judgments  involving  subsumption,  or  the  definition  of  the  word 
heard,  required  moi"e  time  than  mere  association,  when  they  were 
at  all  complex.  But  when  very  simple,  the  minimum  time  for  such 
judgments  was  about  that  of  association  ;  and  the  mean  value  of 
"  subsumption-time  "  (0.766)  differed  but  very  little  from  the  mean 
value  of  "association-time."  Thus  it  required  1.403  sec.  to  judge 
that  a  "  ray  "  is  a  "form  of  the  motion  of  light  ;  "  2.023  to  judge 

■  Philosoph.  Studien,  I.,  heft  ii.,  p.  345  f. 


MCJLTIPLIC AXIOMS'   OF   TWO   ^STUMBERS.  493 

that  "  fame  "  is  a  "  form  of  the  ascription  of  praise  ;  "  and  1.899  to 
judge  that  "  art  "  is  an  "  aesthetic  activity  "  of  man  ;  but  only  0.391 
sec.  to  recognize  a  "mast  "as  a  "part  of  a  ship,"  and  0.469  to 
identify  "egg"  and  "cell." 

The  time  necessary  for  multiplying,  in  the  head,  tioo  numbers  of 
one  figure  each  has  also  been  investigated  by  von  Vintschgau. ' 
The  psycho-physical  processes  involved  in  this  achievement  are 
necessarily  somewhat  complex.  The  influence  of  association  must 
vary  largely,  according  to  the  number  of  times  we  have  previously 
made  the  same  or  any  very  similar  calculation.  For  example,  the 
whole  process  involved  in  answering  the  question,  How  much  is 
1x1?  is  different  from  that  involved  when  the  numbers  are  8x12; 
much  more  different  when  they  are  quite  unfamiliar— as,  e.g., 
76  X  89.  The  order  of  the  numbers  is  not  indifferent ;  as  a  rule, 
reaction  is  quicker  and  more  correct  when  the  smaller  number  pre- 
cedes. The  mean  reaction-time  for  multiplying  two  numbers  (1  to 
10)  was  0.211  sec.  for  L.,  0.207  for  P.,  and  0.259  for  V.,  when  repro- 
duction was  with  the  finger;  and  0.200  for  L.,  0.252  for  P.,  0.248 
for  v.,  when  reproduction  was  with  the  lip.  Of  this,  0.049  for  L. 
reproducing  with  the  finger,  and  0.096  with  the  lip  ;  0.051  for  P. 
with  the  finger,  and  0.082  with  the  lip  ;  and  0.098  for  V.  with  the 
finger,  and  0.087  with  the  lip — are  calculated  to  have  been  due  to 
the  cerebral  processes  involved  in  the  calculation.  As  might  be 
expected,  any  great  increase  in  the  speed  was  found  to  be  accom- 
panied by  an  increase  in  the  number  of  mistakes. 

Cattell,'^  after  objecting  on  good  grounds  that  the  results  of 
the  laboratory  are  always  too  artificial  and  often  too  incorrect  to 
"  give  the  time  it  takes  a  man  to  perceive,  to  will,  and  to  think," 
attempted  to  do  away  with  "involved  methods  and  complicated 
apparatus,"  and  in  simpler  fashion  determine  the  time  Ave  usually 
require  to  see  and  name  an  object,  such  as  a  letter  or  a  color.  He 
concludes  that  to  see  and  name  letters  requires  from  ^  to  \  sec. 
for  each  letter,  and  to  see  and  name  words  that  do  not  make  sen- 
tences requires  \io  ^  sec.  When  the  words  are  connected  into  sen- 
tences it  requires  only  about  one-half  as  much  time  to  name  them 
— the  rate  at  which  one  can  read  varying  from  0.138  to  0.484  sec. 
for  each  word,  according  to  one's  degree  of  familiarity  with  the 
language.  Single  letters  can  be  named  more  rapidly  when  several 
are  in  view  at  the  same  time  ;  nearly  all  persons  are  helped  by  hav- 
ing as  many  as  three,  and  most  persons  by  having  as  many  as  four 

^  See  Pfliiger's  Archiv,  xxxvii.,  pp.  127  ff. 

'  See  Mind,  January,  1886,  p.  63  f.;  and  Wundt's  Philosoph.  Studien,  II., 
heft  iv.,  pp.  635  fE. 


494:  COMPLEX   REACTIOISr-TIME. 

or  five,  letters  in  view  at  the  same  time.  That  is  to  say  (using 
Wundt's  figure  of  speech),  the  time  of  perception,  or  field  of  con- 
sciousness, covers  the  time  of  apperception,  or  clear  spot  of  con- 
sciousness ;  while  one  presentation  of  sense  is  at  the  focus  of 
consciousness,  several  others  may  be  coming  toward  the  focus 
from  the  background  of  consciousness.  The  second  letter  in  view 
shortens  the  time  of  apperception  about  j^g ;  the  third,  gJ^ ;  the  fourth, 
Y-^u  ;  the  fifth,  ^^-^  sec. 

§  26.  Finally,  the  closing  remark  of  the  foregoing  paragraph  in- 
troduces the  inquiry  into  the  "circuit  of  consciousness" — that  is, 
the  number  of  impressions  which  can  exist  within  the  field  of  con- 
scious perception  at  any  one  time  ?  This  question  has  been  much 
debated  on  abstract  or  metaphysical  grounds  touching  the  nature 
of  the  soul.  Since  the  soul  is  one  and  simjDle — it  has  been  claimed — 
there  can  be  before  it  but  one  object  at  the  same  instant  of  time  ; 
but  since  all  its  knowledge  is  relative,  the  claim  has  also  been 
made  that  at  least  two  impressions  are  always  contemporaneous  in 
consciousness.  Hamilton,'  on  the  contrary,  concluded,  from  ob- 
serving his  own  mental  activities,  that  the  circuit  of  consciousness 
could  embrace  as  many  as  six  or  seven  distinct  simultaneous  im- 
pressions. It  is  evident  that  only  an  appeal  to  facts  can  decide 
such  a  dispute  ;  it  is  also  evident  that  the  manner  of  appeal  should 
be  more  precise  and  scientific  than  the  one  proposed  by  Hamilton. 

Experiments  have  therefore  been  instituted  to  determine  the 
"  circuit  of  consciousness,'"'  by  finding  how  many  regularly'recurrent 
successive  impressions  of  sound,  for  example,  can  be  so  far  united 
into  one  mental  image  as  to  have  their  likeness  or  unlikeness  to 
another  similar  series  clearly  discerned.  The  method  of  experi- 
ment employed  by  Dietze "  was  the  following  :  The  stroke  of  a  pen- 
dulum, heard  at  regular  iuteiwals,  was  employed  as  the  stimulus. 
After  a  single  stroke  as  a  warning,  a  series  of  successive  strokes 
was  given,  which  was  begun  and  ended  by  the  sounding  of  a  clock- 
bell  simultaneously  with  a  stroke  of  the  pendulum.  Another  series 
of  strokes  of  the  pendulum  followed  immediately  upon  the  sound 
which  announced  that  the  first  series  was  closed.  The  second  se- 
ries was  ended  by  simply  stopping  the  pendulum.  A  fixed  number 
of  strokes  constituted  the  first  series  ;  a  variable  number  (either  one 
more  or  one  less  than  the  first  series)  constituted  the  second.  The 
question  projDosed  for  answer  Avas  :  How  man}'  impressions  of  sound 
can  be  received  in  the  first  series  and  the  relation  of  the  second 
series  to  the  first  (as  equal,  greater,  or  less)  be  accurately  discerned 

'  Lectures  on  Metaphysics,  p.  165.  f. ,  and  elsewhere      Boston,  I860, 
^  Article  in  Philosoph.,  Studien,  II.,  heft  iii.,  pp.  362  fE. 


'effects    of   practice   and   ATTENTION".  495 

without  counting  ?  The  effect  upon  the  subject  of  such  an  experi- 
ment may  be  described  as  that  of  sending  through  the  focus  of  con- 
sciousness a  train  of  impressions,  in  regular  succession,  from  the 
obscure  regions  of  perception  at  which  they  enter  to  the  obscure 
regions  at  which  they  depart  from  the  field  of  consciousness.  An 
image  of  the  whole  field  of  consciousness,  with  the  line  of  march  of 
the  impressions,  must  be  formed  in  order  accurately  to  compare  two 
series  like  those  described.  The  result  of  such  experiments  showed 
that  the  number  of  successive  impressions  which  can  be  comprised 
within  the  circuit  of  consciousness  depends  upon  the  rate  with 
which  they  succeed  each  other.  The  most  favorable  interval  was 
found  to  be  0.2-0.3  sec.  ;  with  this  interval  most  of  the  subjects  of 
experiment  attained  a  high  degree  of  accuracy  for  even  as  many  as 
ten  or  twelve  impressions.'  Individual  difierences  were  marked, 
however;  thus,  for  one  subject,  the  time  of  0.21  sec.  interval  was 
too  great  for  the  maximum  of  accuracy,  and  2.0  sec.  was  so  lai'ge 
as  to  prevent  his  having  any  satisfactory  apperception  of  even  a 
single  impression.  The  manner  of  uniting  the  impressions  was 
also  found  to  have  a  great  effect  upon  the  circuit  of  consciousness. 
When  the  process  of  apprehension  was  allowed  to  have  a  rhythmic 
form  of  grouping  the  impressions,  the  number  possible  in  a  single 
field  of  consciousness  was  increased.  Without  grouping,  16  was 
the  maximum  even  number,  15  the  maximum  odd  number,  at- 
tained. Rhythmic  grouping  raised  this  number  to  40,  or  a  little 
more,  as  the  maximum  even  number,  and  to  35;  37,  and  39  as  the 
maximum  odd  numbers.  It  is  possible,  then,  to  apprehend  a  larger 
even  number  than  odd  number  of  impressions  in  a  siugie  circuit 
of  consciousness.  Certain  numbers,  perhaps  those  most  familiarly 
grouped  in  experience,  seem  also  to  have  the  jDreference  over 
others. 

§  27.  In  all  experiments  to  determine  the  time-relations  of  mental 
phenomena,  the  effects  of  practice  and  attention  in  diminishing 
psycho-physical,  time,  and  oi  fatigue  to  increase  it,  are  made  ap- 
parent. Certain  special  experiments  have  also  been  instituted  to 
show  how  illness,  old  age,  and  drugs  operate  upon  the  speed  of 
psycho-physical  time.  Thus  MerkeP  found  that  the  will-time  ne- 
cessary- for  choice  between  two  motions  was  reduced  by  practice,  for 
three  subjects  of  experiment,  from  0.080  sec.  to  0.050,  from  0.097 
to  0.0535,  and  from  0.098  to  0.062,  respectively.    For  choice  among 

'  See  Dietze's  statement.  Pliilosopli.  Stiidien,  III.,  lieftiii.,  p.  386,  and  a 
note,  p.  384,  correcting  the  erronous  conclusion  drawn  by  M.  Ribot  (German 
Psychology  of  To-day,  p.  278,  New  York.  1886 j. 

■'  Wuudt's  Philosoph.  Studien,  II.,  heft  i.,  p.  110  f. 


496  COMPLEX   EEACTION-TIME. 

five  and  ten  possible  motions,  the  effect  of  practice  was  yet  more 
marked  :  thus,  with  five  possible  choices,  the  will-time  of  one  per- 
son was  reduced  by  practice  from  0.239  sec.  to  0.083  ;  and  of  an- 
other, with  ten  possible  choices,  fi'om  0.358  to  0.094.  For  each 
single  day's  series  of  experiments,  the  time  diminished  faster  at  first 
than  subsequently ;  but,  in  many  cases,  more  distinctly  on  the  second 
than  on  the  first  day  of  experiment.  Ivries  and  Auerbach '  discov- 
ered that,  after  a  short  time,  further  practice  has  no  influence  on  sim- 
ple reaction-time  ;  but  some  practice  is  necessary  to  give  any  reliable 
value  to  such  time.  The  effect  of  practice  on  discernment- time  is 
very  different.  In  the  experiments  upon  the  localization  of  tactile  sen- 
sations, the  discernment-time  for  A.  was  at  first  as  great  as  0.064  sec, 
or  even  0.117,  but  afterwai-d  fell  to  a  mean  of  0.021.  Discernment- 
time  continues  to  decrease  by  practice,  after  all  diminution  of  sim- 
ple reaction-time  has  ceased  ;  it  is  also  transferable  to  other  regions 
of  the  same  sense.  Trautscholdt  ^  found  that  practice  for  fourteen 
days  reduced  the  "word-reaction-time"  of  one  subject  from  0.309 
sec.  to  0.149  ;  association-time  was  found  to  be  sensitive  to  practice 
in  a  much  smaller  degree.  The  effect  of  attention  must  also  al- 
ways be  taken  into  account.  It  was,  ajDparently,  by  guarding  this 
carefully,  and  by  practice,  that  Kries  and  Auerbach  succeeded  in 
obtaining  such  small  values  for  discernment-time.  The  effect  of 
distracting  the  attention  was  observed  by  Wundt,^  who  introduced 
disturbing  sensations  of  the  same  or  of  a  different  sense  into  series 
of  regularly  recurring  impressions.  Thus,  the  mean  reaction-time 
for  a  weak  impression  of  sound  was  lengthened  from  0.189  to  0.313 
sec,  by  a  disturbing  noise  ;  and  for  a  strong  impression  of  sound, 
from  0,158  to  0.203  sec.  The  mean  reaction-time  for  sight  of  an 
electric  spark  was  increased  from  0.222  to  0.300  by  a  disturbing 
noise  occurring  simultaneously. 

All  the  experiments  also  make  obvious  the  great  influence  of 
individual  peculiarities.  But  this  influence  may  not  be  in  the  di- 
rection in  which  it  would  most  readily  be  supposed  to  lie.  For 
example,  Exner "  found  that,  of  two  young  men,  one  of  whom  had  a 
very  lively  temperament  and  the  other  not,  the  former  had  much  the 
longer  simple  reaction-time  (0.3311  sec.  as  compared  with  0.1337). 
The  reaction-time  of  a  man  of  seventy-seven,  taken  from  the  alms- 
house, was  at  first  0.9952  sec. ;  this  was,  however,  reduced  by  practice 
to  0.1866  sec.     The  enervation  produced  by  a  hot  summer's  day,  or 

'  Archiv  f.  Anat.  u.  Physiol.,  Physiolog.  Abth.,  1877,  p  361  f. 

*  Wundt's  Philosoph.  Studien,  I.,  heft  ii.,  p   237  f. 
^  Physiolog.  Psychologie,  ii. ,  p.  243. 

*  Hermanri's  Handb.  d,  Physiol.,  II.,  ii.,  p.  268. 


THE   RESULTS   OF   EXPERIMENT.  497 

the  exhaustion  of  a  sleepless  night,  or  bad  news,  etc.,  increases  the 
reaction-time.  A  small  quantity  of  wine,  slowly  drunk,  decreased 
the  reaction-time  ;  but  a  larger  quantity  increased  it  from  0. 1904 
sec.  to  0.2969,  although  the  subject  of  the  experiment  considered 
himself  to  be  reacting  more  promptly  than  usual.  Coffee  begins  to 
decrease  the  reaction-time  at  20-25  minutes  after  it  is  taken,  and 
continues  this  effect  for  about  2  hours.  Subcutaneous  injections 
of  morphine  delay '  it ;  but  this  effect  does  not  last  long  unless  the 
injection  is  repeated.  Obersteiner  found  that  a  subject  whose  re- 
action-time in  the  first  stage  of  paralysis  was  0.166  sec,  gradually 
lost  control  of  himself  until,  in  the  last  stages  when  experiment  was 
possible,  the  interval  was  0.281-0.753.  Buccola,  who  has  experi- 
mented upon  idiots,  imbeciles,  epileptics,  etc.,  finds  that  the  dura- 
tion of  perception  is  lengthened  in  all  these  cases,  with  the  exception 
of  some  forms  of  abnormal  excitement. 

§  28.  On  summing  up  the  results  of  all  the  experiments  hitherto 
made  in  psychometry,  we  can  only  reiterate  what  we  began  by  say- 
ing:  Experimental  research  does  not  explain  the  origin  or  nature 
of  our  idea  of  time  and  its  relations,  nor  has  it  succeeded  in  estab- 
lishing many  new  principles  of  great  moment  for  psychology.  It 
is,  however,  a  vigorous  and  promising  branch  of  psycho-physical 
study.  It  has  placed  upoii  a  scientific  basis,  and  defined  in  accurate 
mathematical  terms,  many  of  our  ordinary  impressions  as  to  the 
time-relations  of  mental  phenomena.  The  attempt  to  analyze  psy- 
cho-physical time  seems  to  show  thai  its  various  elements  of  simple 
perception,  apperception,  or  clear  discernment,  and  volition,  occur  in 
the  order  named,  and  yet  ordinarily  overlap  each  other,  as  it  were. 
Practice  and  attention,  under  the  most  favorable  circumstances,  may 
reduce  either  one  nearly  to  zero.  In  this  way,  simple  reaction-time 
becomes  most  nearly  equal  to  purely  physiological  or  reflex  time  ; 
reaction-time,  with  discernment,  is  almost  reduced  to  simple  per- 
ception-time ;  and  the  duration  required  by  will-time  for  solving  a 
dilemma  is  wellnigh  eliminated. 

Conclusions  as  to  the  existence  and  intercerebral  relations  of 
nervous  centres  of  apperception  and  volition  would  be  premature, 
and  probablj''  misleading,  in  the  present  state  of  this  science.  Nor 
have  we  as  large  hopes  as  to  its  ability  "  to  solve  many  of  the  old 
problems  "  in  the  future  as  have  been  expressed  by  some  of  its 
enthusiastic  students. 

'  See  von  Vintschgau  and  Dietl,  in  Pfliiger's  Archiv,  xvL,  pp.  316  ff  ;  and 
Exner,  in  Hermann's  Handb.  d.  Physiol.,  XL,  ii.,  p.  270  f. 

32 


CHAPTEE  IX. 
FEELINGS    AND    MOTIONS. 

§  1.  From  tliis  point  onward  the  study  of  Physiological  Psychol* 
ogy  is  compelled  to  content  itself  with  opinions  much  more  in- 
definite and  uncertain  even  than  those  to  which  we  have  already 
become  accustomed.  Theories  of  the  localization  of  cerebral  func- 
tion, of  the  quantity  and  quality  of  sensations  and  their  combina- 
tion into  presentations  of  sense,  and  of  the  time-relations  of  mental 
phenomena,  admit  to  a  considei'able  extent  of  experimental  tests. 
But  the  feehngs  and  their  physical  basis  elude  the  efforts  made  to 
subject  them  to  the  conditions  of  a  strictly  scientific  investigation. 
The  same  complaint  may  be  justified  concerning  all  opinions  as 
to  the  physical  basis  of  the  higher  intellectual  operations,  and  as 
to  the  effect  of  age,  temperament,  sex,  and  race,  upon  the  character 
and  development  of  the  mind.  No  attempt  whatever  will  be  made 
to  conceal  the  meagre,  obscure,  and  doubtful  character  of  the  evi- 
dence upon  which  our  conjectures  must  be  based.  Indeed,  on 
these  matters  nothing  but  the  greatest  caution  is  fitted  to  inspire 
confidence  ;  the  supreme  wisdom  is  not  infrequently  a  frank  con- 
fession of  ignorance  or  uncertainty. 

About  our  "Feelings"  so-called — their  nature,  origin,  relation 
to  a  physical  basis  and  to  sensations  and  ideas — we  know  remark- 
ably little.  Nor  has  any  classification  of  the  feelings  hitherto  been 
made  which  is  entitled  to  command  general  assent.  The  reason 
for  this  fact  is  not  difficult  to  discover.  By  their  very  nature,  the 
phenomena  are  obscure,  indefinite,  and  3'et  extremely  variable  and 
multiform.  They  are  also  connected  with  our  sensations  and  ideas 
in  such  a  way  as  to  make  all  separation  in  fact  quite  impossible. 
The  psychology  of  the  feelings,  as  studied  from  the  introspective 
point  of  view,  has  therefore  always  been  peculiarly  unproductive 
of  assured  results.  The  fact  that  their  physiological  conditions 
are  laid  so  largely  in  obscure,  rapid,  and  infinitely  varied  changes 
within  the  central  organs,  such  as  cannot  be  either  directly  ob- 
served or  indirectly  subjected  to  experimentation,  increases  the 
difficulties  of  the  subject.     What  is  the  nature  of  feeling  ?     How  do 


DIFFERENT   THEORIES   OF   FEELING.  499 

the  different  feelings  differ,  and  what  elements  have  they  in  com- 
mon ?  Under  what  conditions  do  we  have  sensiious  feelings  ;  and 
tinder  what  conditions  are  these  feelings  pleasant  or  unpleasant  ? 
Is  feeling  ever  perfectly  indifferent  ;  is  there  a  zero-point  of  feel- 
ing ?  How  are  the  feelings  related  to  the  quality  and  intensity  of 
physical  stimuli  ?  What  is  the  physiological  basis  (if  any  exist)  of 
the  higher  sesthetic,  moral,  and  religious  feelings  ?  '  These  and 
other  similar  questions  may  be  asked  of  psycho-physical  science 
with  little  satisfactory  result, 

§  2.  Many  diverse  views  have  been  held  as  to  the  essential  na- 
ture of.  feeling.  These  views  may,  for  the  most  part,  however,  be 
classified  under  two  heads :  They  are  either  such  as  emphasize  the 
dependence  of  the  feelings  on  bodily  conditions,  and  so  resort  to 
physiological  explanation  of  their  origin  and  nature  ;  or  else  they 
are  such  as  emphasize  their  dependence  upon  relations  that  obtain 
among  the  so-called  "  ideas,"  or  purely  mental  states  and  products 
of  the  mind.  The  extreme  form  of  one  of  these  two  theories  holds 
that  feeling  is  always  merely  a  consciousness  of  a  certain  condition 
of  the  nervous  elements.  The  extreme  form  of  the  other  leads  to 
the  position  from  which  all  feeling  is  regarded  as  a  sort  of  sec- 
ondary consciousness  of  the  "  furtherance  "or  "  hindrance  "  of  one 
idea  by  another.  The  principal  real  ground  for  the  former  theory 
lies  in  the  fact  that  certain  conditions  of  the  nervous  elements  under 
stimulation  are,  as  a  rule,  followed  by  painful,  and  certain  others  by 
pleasurable,  feeling.  The  latter  theory  is  based  solely  upon  the  truth 
that  certain  mental  states  called  "ideas  "  are,  as  a  rule,  accompanied 
or  followed  by  corresponding  modes  of  being  affected  which  have 
the  characteristic  tone  of  all  feeling — that  is,  are  either  agreeable  or 
disagreeable.  Neither  of  these  views,  however,  serves  to  define  the 
essential  nature  of  feeling,  since  to  feel  is  as  simple  and  funda- 
mental an  operation  of  mind  as  it  is  to  know.  Feeling  can  never 
be  stated  in  terms  of  knowledge.  Inasmuch,  then,  as  all  definition 
is  only  the  expression  of  an  elaborate  and  complex  form  of  knowl- 
edge, the  nature  of  feeling  is  not  capable  of  being  defined  ;  it 
must  he  felt.  When,  then,  this  nature  is  defined  as  consisting  in 
some  relation  to  physical  sensation  or  to  mental  images,  it  is  de- 
prived of  the  very  characteristic  which  makes  it  to  he  feeling  rather 
than  sensation  or  idea.  Both  theories,  however,  have  succeeded  in 
stating  certain  conditions  or  antecedents  of  the  reaction  of  mind  in 
the  way  of  feeling. 

§  3.  The  foundations  for  a  physiological  theory  of  the  feelings 

'  Comp.  Horwicz,  Psycliologische  Analysen,  i. ,  p.  21  f. 


500  NATUKE   AISTD   KINDS   OF   FEELING. 

were  laid  by  Lotze, '  with  that  blending  of  scientific  caution  and  psy- 
chological insight  which  characterize  most  of  his  work.  ■  He  distin- 
guished the  feelings,  as  mental  conditions  of  pain  or  pleasure,  from 
sensations  as  indifferent  elements  of  our  percejDts  of  things.  Yet, 
in  fact,  sensations  are  always,  or  usually,  colored  wdth  feeling  ;  and 
analysis  is  therefore  obliged  here  to  distinguish  in  theory  what  co- 
exists in  fact.  Feelings  are  of  two  hinds  :  "  sensuous,"  as  coming 
from  bodily  impressions  ;  and  "  intellectual,"  as  flowing  from  the 
relations  of  ideas.  Pleasurable  feelings  always  arise  from  the  co- 
incidence, and  painful  from  the  opposition,  between  the  effects  of 
the  stimulus  and  any  one  of  those  conditions  to  which  the  regular 
expression  of  the  bodily  or  spiritual  life  is  attached.  Yet  even  this 
statement  is  not  true  without  making  further  explanations  and 
Umitations.  For  something  bitter  may  be  harmless,  or  even  bene- 
ficial ;  and  acetate  of  lead  may  be  sweet  and  pleasant,  but  deadly. 
More  precisely,  then,  "feeling  is,  in  general,  only  the  measure  of 
the  partial  and  momentary  concord  between  the  effect  of  the  stimu- 
lus and  the  conditions  of  vital  activity.""  Lotze  was  far  too  keen 
a  psychologist,  however,  to  suppose  that  in  laying  down  this  law 
he  was  explaining  the  nature  of  feeling  as  a  secondary  and  derived 
form  of  consciousness.  He  has  himself  vindicated  its  right  to  be 
regarded  as  primitive,  and  not  deducible  from  either  sensations  or 
ideas.^  But  even  in  the  way  in  which  he  understood  his  own 
theory,  much  doubt  may  be  thrown  upon  its  truth. 

It  is  admitted  by  all  that  certain  intensities  of  nearly  all  forms  of 
stimuli  are  both  productive  of  painful  feeling  and  also  antagonistic 
to  the  vital  conditions  of  the  organism.  Undoubtedly,  also,  suffering 
is  both  an  indication  and  a  cause  of  abnormal  and  injurious  action  of 
the  nervous  mechanism.  But  that  the  feeling  of  jDain  measures  the 
degree  of  this  antagonism,  or  that  everything  found  at  the  time  dis- 
agreeable is  in  any  degree  demonstrably  opposed  to  the  vital  wel- 
fare of  the  organism,  cannot  be  assumed;  and  the  alleged  law  even 
seems  incompatible  with  the  individual  peculiarities  which  charac- 
tex'ize  what  is  agreeable  or  disagreeable  to  the  senses  of  different 
persons.  The  excessive  stimulus  of  the  surgeon's  knife  is  not  .ren- 
dered any  more  really  in  accord  with  the  conditions  of  the  vital 
activity  of  the  organ  to  which  it  is  applied  by  the  fact  that  anaes- 
thetics prevent  the  pain  which  would  otherwise  result.  An  exces- 
sive and  immediately  injurious  stimulation  of  considerable  portions 
of  the  body  may  be  accompanied  by  a  large  amount  of  positive 

'  Medicin.  Psychologie,  pp.  233  ff.  -  Ibid. 

•'See  Metaphysic,  p.  474,  Oxford,  1884;  and  Microcosmus,  i.  p.  177  1, 
Edinburgh,  1885. 


PHYSIOLOGICAL   LAW   OF   FEELING.  501 

pleasure  or,  at  most,  with  very  little  pain,  wliile  a  small  and  quite 
harmless  degree  of  another  kind  of  stimulation  may  result  in  great 
discomfort.  Attention,  association,  and  control  of  the  "will  have 
also  much  to  do  with  determining  the  subjective  state  which  is  con- 
nected with  any  given  relation  between  the  effect  of  the  stimulus 
and  the  conditions  of  vital  activity. 

§  4.  More  recent  attempts  to  give  a  general  physiological  law  for 
the  phenomena  of  pleasurable  and  painful  feeling  can  scarcely  be 
said  to  be  any  more  satisfactory.  It  is  true,  as  Bain '  declares,  that 
"a  very  considerable  number  of  the  facts  maybe  brought  under 
the  following  principle,  namely,  that  states  of  pleasure  are  connected 
iviih  an  increase,  and  states  of  pain  with  an  abatement,  of  some,  or  all, 
of  the  vital  functions."  But  other  facts  in  no  small  number  cannot 
be  brought  under  this  principle.  It  is  not  a  difficult  task  for  the 
physician  to  abate  all  the  vital  functions  of  the  patient,  even  down 
to  or  beyond  the  line  of  danger,  with  the  immediate  result  of  pro- 
ducing pleasure  rather  than  pain.  After  objecting  to  Bain's  state- 
ment as  being  "too  vague,"  etc.,  Grant  Allen ^  declares  the  true 
principle  of  connection  to  be  the  following  :  "  Pleasure  is  the  con- 
comitant of  the  healthy  action  of  any  or  all  of  the  organs  or  mem- 
bers supplied  with  afferent  cerebro-spinal  nerves,  to  an  extent  not 
exceeding  the  ordinary  powers  of  repai-ation  possessed  by  the  sys- 
tem." Esthetic  pleasure  he  provisionally  defines  as  "the  subjec- 
tive concomitant  of  the  normal  amount  of  activity,  not  directly 
connected  with  life-serving  function,  in  the  peripheral  end-organs 
of  the  cerebro-spinal  nervous  system."  ^  Now,  that  pleasure  is  the 
reflex  of  healthy  and  unimj)eded  activity  is  an  old  psychological 
truism  ;  and  that  we  are  dependent  upon  impulses  propagated  in 
the  sensory  nerves  of  the  cerebro-spinal  system  for  sensations, 
pleasureable  or  painful,  of  muscular,  organic,  or  more  special  sort, 
scarcely  needs  statement  as  a  newly  discovered  law  of  "physiolooi- 
cal  sesthetics."  Nothing,  however,  could  well  be  more  "vague" 
than  the  limit  fixed  by  the  words  "  to  an  extent  not  exceeding  the 
ordinary  powers  of  reparation  possessed  by  the  system."  Does  the 
man  whose  powers  of  nervous  reparation  are  extraordinarily  great 
necessarily  find  his  quinine  any  the  pleasanter?  The  statement 
that  pain  is  a  warning  of  danger  from  excessive  or  abnormal  activ- 
ity of  the  nervous  system  must,  of  course,  be  accepted  as  summing 
up  a  large  number  of  facts ;  but  there  are  other  facts  not  easily 
brought  under  such  statement.    Moreover,  until  we  have  some  objec- 

'  The  Senses  and  the  Intellect,  p.  281  f. 

^  Physiological  Esthetics,  London,  1877,  p.  31. 

3  Ibid.,  p.  34. 


502  KATURE   AND   KINDS    OF   FEELING. 

tive  means  of  determining  what  is  the  "  normal  amount"  of  function 
in  any  tissue,  the  alleged  law  that  pleasure  is  "  the  subjective  con- 
comitant "  of  such  amount  is  of  little  or  no  value.  The  whole  sub- 
ject is  left  in  that  indefinite  condition  which  invites  us,  on  the  one 
hand,  to  consider  pain  as  the  proof  that  the  function  of  the  nervous 
system  which  occasions  it  is  destructive  ;  and  then  tells  us,  on  the 
other  hand,  that  the  essence  of  the  pain  is  in  its  being  the  subjec- 
tive concomitant  of  such  function. 

§  5.  But  if  purely  physiological  theories  of  feeling  do  not  suc- 
ceed in  defining  its  nature,  or  in  stating  the  relation  between  the 
action  of  the  nerves  and  the  pleasureable  or  painful  tone  of  the 
feeling,  the  success  of  the  second  class  of  theories  is  no  greater. 
Of  this  class  the  views  of  Nahlowsky/  as  set  forth  in  his  interest- 
ing monogTaph,  are  perhaps  the  best  example.  This  author  begins 
by  drawing  a  sharp  distinction  between  sensation  and  feeling.  The 
"  tone  "  of  sensations  as  pleasant  or  unpleasant  he  would  not  call 
by  the  term  "feelwg ; "  such  tone  is  rather  that  which  gives  us 
"  the  how  "  ("  Wis  ")  of  the  sensation,  and  depends  for  its  pleasant, 
or  unpleasant  character  upon  whether  the  effect  of  the  stimulus 
furthers  or  inhibits  the  functions  of  the  vegetative  life.  Even  those 
states  of  consciousness  which  are  constituted  from  various  ele- 
ments due  to  stimulations  of  the  nerves  at  various  quarters  not  defi- 
nitely localized,  and  ordinarily  called  "  common  feeling,"  Nahlow- 
sky  would  define  as  "common  sensations."  Pain  also  is  a  sensation 
and  not  a  feeling.  But  feeling,  according  to  this  author,  is  neither 
tone  nor  quality  of  sensation  ;  though  it  may  be  an  elevation  or  de- 
pression of  mind  produced  indirectly  by  the  sensations.  FeelingSj 
properly  characterized,  comprise  all  the  conditions  resulting  from 
the  simultaneous  existence  of  ideas  in  the  mind,  which  either  sup- 
poi't  or  interfere  with  each  other.  In  the  former  case,  they  are 
agreeable  ;  in  the  latter,  disagreeable.  They  are,  then,  secondary 
conditions  of  mind,  dependent  on  ideas,  recognized  as  not  of  bodily 
origin,  but  as  having  a  content  of  a  mental  rather  than  physical  order. 
Hunger,  thirst,  weariness,  shivering,  etc.,  are  sensations  ;  sympathy 
love,  gratitude,  reverence,  admiration,  etc.,  are  feelings.  According- 
ly', feeling  is  defined  as  "  the  immediate  consciousness  of  the  momen- 
tary rising  or  depression  of  one's  own  psychical  activity  "  (that  is,  of 
the  movement  of  the  ideas) .  Even  to  the  affections  this  theory  would 
deny  a  place  among  the  kinds  of  feeling — for  the  former  spring 
from  the  latter  under  the  mediating  influence  of  organic  effects. 

The  foregoing  view  of  the  nature  of  feeling  is  adhered  to  sub- 

'  Das  Gefiililslebeii,  in  seiuer  wesentlichsten  Ersclieinungen  u.  Beziigen, 
2d  ed.     Leipzig,  1884. 


PSTCHOLOGICAL   THEORY    OF   FEELHSTG.  508 

stantially  by  many  others,  especially  by  the  followers  of  Herbart. 
Thus  Drbal '  holds  that  feelings  are  not  primitive  states  of  mind, 
but  result  from  the  reciprocal  action  of  ideas — if  this  ideating  ac- 
tivity is  one  of  reciprocal  inhibition,  the  feeling  which  is  the  be- 
coming conscious  of  the  inhibition  is  unpleasant ;  if  the  activity  is 
one  of  reciprocal  combination,  the  conscious  feeling  of  this  fact  is 
pleasant.  Feeling  in  general  is  therefore  the  immediate  conscious- 
ness of  the  rising  or  falling  of  one's  power  of  ideating,  as  it  were. 
Beneke,''  also,  considers  that  two  mental  images  excited  belong  to 
every  feeling  ;  of  these,  one  is  that  which  is  felt,  and  the  other  is 
one  "  against "  which  the  first  is  felt.  Feeling  and  no-feeling,  or 
this  or  that  feeling,  can  therefore  attach  itself  to  one  and  the  same 
image.  Volkmann  von  Volkmar,  in  his  great  work,'  considers  feeling 
as  the  consciousness  of  the  process  of  ideation  itself  as  distinguished 
from  consciousness  of  this  or  that  idea,  and  it  is  conditioned  upon 
some  resistance  being  offered  to  the  process.  Feeling  is,  then,  nft 
one  proper  idea,  to  be  placed  in  conjunction  or  classed  with  others. 
It  is  rather  a  becoming  conscious  of  the  degree  of  tension,  as  it  were, 
which  characterizes  the  process  of  ideation  at  each  particular  mo- 
ment. The  condition  of  the  origin  of  a  feeling  is,  then,  the  existence 
of  two  simultaneous  opposed  ideas.  Their  coexistence  occasions 
a  state  of  tension  ("  Spannung  "),  as  it  were,  and  this  state  gives 
way  as  one  idea  triumphs  over  the  other.  The  type  of  simple  feel- 
ing may  be  illustrated  by  the  condition  in  which  the  mind  finds 
itself  when  listening  to  harmonious  or  discordant  musical  sounds. 

§  6.  The  theory  which  makes  feeling  a  derived  consciousness  de- 
pendent upon  the  relations  of  the  ideas  as  furthering  or  checking 
each  other  is  unsatisfactory.  It  cannot  be  admitted,  to  begin  with, 
that  feeling  is  a  secondary  or  derived  form  of  consciousness.  No 
form  of  mental  activity  is  more  primitive  and  unanalyzable  than 
feeling  ;  none  is  earlier  in  the  development  of  mental  life.^  Be- 
fore the  infant  has  localized  the  different  sensations,  and  combined 
them  into  percepts  of  the  different  parts  of  its  own  organism, 
the  consciousness  of  being  affected  in  a  given  way,  either  pleasur- 
able or  not,  must  predominate.  Other  forms  of  feeling — of  desire, 
uneasiness,  comfort,  etc. — are  inseparably  connected  with  its  first 
states  of  consciousness  ;  they  belong  to  its  inherited  impulses  and 

'  Lehrbuch  d.  empirisclien  Psychologie,  2d  ed.,  pp.  200  ff.     Wien,  1875. 

^  Lehrbuch  d.  Psychologie  als  Naturwissenschaft,  pp.  170  ff.     Berlin,  1877. 

3  Lehrbuch  d.  Psychologie,  II.,  pp.  298  fif. 

*  This  view  of  the  feelings  is  maintained  by  Horwicz,  and  developed  at  length, 
polemically,  by  Lotze  (Horwicz,  Psychologische  Analysen,  i. ,  p.  168  f . ;  Lotze, 
Medicin.  Psychologie,  p.  235  f . ;  and  references  already  cited  in  note  p.  500), 


n04  JSTATUEE   AND   KINDS   OF   FEELING. 

instinctis,  and  are  only  later  definitely  related  to  the  appropriate 
ideas.  The  primary  formation  of  self-consciousness  is  quite  as 
truly  connected  with  self-feeling,  pleasurable  or  painful,  as  with 
the  process  of  ideation  in  constructing  the  concept  of  "me  "and 
"not-me." 

Moreover,  although  we  are  to  distinguish  sensation  from  feeling, 
we  must  regard  the  feeling  which  inseparably  accompanies  sensa' 
tion  as  feeling,  strictly  speaking,  and  not  as  tone  of  sensation  ;  or, 
in  other  words,  the  tone  of  every  sensation,  as  either  pleasurable 
or  painful,  is  given  to  it  by  the  feeling  which  accompanies  and 
blends  with  it.  The  sensation,  as  having  a  certain  quality,  quan- 
tity, and  locality,  is  capable  of  being  built  into  a  "Thing"  which 
the  mind  perceives  as  not-itself.  But  the  feeling,  the  pleasurable 
or  painful  tone  of  the  sensation,  is  always  recognized  as  purely  and 
simply  a  way  in  which  the  mind  is  affected.  To  refuse  to  speak  of 
sensations  and  emotions,  with  all  their  complicated  physical  basis, 
as  belonging  at  all  in  the  realm  of  "  feeling,"  is  to  restrict  the  use 
of  the  word  unwarrantably.  The  Herbartian  theory  commits  in 
this  matter  the  mistake  which  it  is  guilty  of  committing  repeatedly  ; 
it  regards  the  "  ideas  "  as  realities  that  have  in  some  sort  a  sub- 
stantial existence,  and  can  do  something  by  way  of  furthering  or 
hindering  each  other.  But  ideas  are  themselves  nothing  more  than 
mental  products  that  exist  only  when  and  so  long  as  the  mind  acts 
with  a  definite  degree  and  kind  of  energy.  In  determining  the 
kind  and  degree  of  this  ideating  energy,  the  previous  action  and 
habit  of  the  mind  by  way  of  feeling  is  quite  as  influential  upon  the 
mode  of  feeling  as  is  the  manner  of  its  ideating  energy.  Finally, 
this  theory  wrecks  itself  upon  the  denial  of  all  that  which  the  phys- 
iological theory  maintains  and  establishes.  The  two  theories,  then, 
supplement  and  correct  each  other  ;  but  even  when  combined  they 
only  tell  us  in  pai-t  what  are  the  physical  and  mental  conditions 
under  which  feeling  arises. 

§  7.  The  truth  appears  to  be  as  follows  :  Feeling  is  an  original 
and  under ived  form  of  consciousness,  or  mode  of  the  operation  of  con- 
scious mind.  It  can  neither  be  defined  by,  nor  deduced  from, 
sensation  or  ideation.  To  know  what  it  is  to  feel,  the  highest  in- 
telligence of  itself  would  be  incapable.  Such  knowledge  comes  only 
from  having  felt.  Feeling  accompanies  all  mental  experience,  both 
that  of  sensation  and  of  the  higher  intellectual  processes.  It  un- 
doubtedly has  a  certain  physical  basis  ;  and  certain  laws  may  be 
stated  which  discover  some  of  the  relations  that  hold  good  between 
conditions  of  the  nervous  system  and  resulting  conditions  of  feel- 
ing.    Certain  other  laws  may  be  laid  down  which  partially  define 


'  CLASSIFICATION   OF   THE   FEELINGS,  505 

the  relations  existing  between  the  purely  intellectual  and  the  feel- 
ing activities,  or  reactions,  of  mind.  These  two  sets  of  laws  give 
us  the  physical  and  the  intellectual  conditions  of  different  tones 
of  feeling  respectively.  But  no  one  law  has  yet  been  discovered 
which  covers  all  the  facts  of  relation,  either  between  feeling  and 
the  bodily  states  or  between  feeling  and  the  ideas.  Nor  is  it  likely 
that  any  such  law  exists  to  be  discovered.  Manifold  relations,  a3 
determined  by  heredity,  individual  peculiarities,  association,  atten- 
tion, etc.,  always  exist,  and  contribute  to  the  complex  result. 

§  8.  The  various  attempts  to  establish  fixed  classes  of  the  feelings 
can  scarcely  be  pronounced  more  satisfactory  than  the  attempts 
to  define  their  nature.  Very  great  difficulties  stand  in  the  way  of 
such  a  classification,  of  which  the  following  are  most  important : 
The  phenomena  are  themselves  very  obscure,  changeable,  and  multi- 
form ;  they  are  also  inextricably  associated  with  the  phenomena  of 
sensation  and  ideation.  Moreover,  the  theory  held  by  any  inquirer 
as  to  the  origin  and  nature  of  the  feelings  is  pretty  sure  to  deter- 
mine his  classification  of  them.  For  example,  two  before-men- 
tioned authorities  (Nahlowsky  '  and  Drbal  ^),  as  a  result  of  the 
"ideational"  theory',  divide  the  feelings  into  (1)  such  as  are  de- 
pendent on  the  forvi  of  the  course  of  ideas,  and  (2)  such  as  ai'O 
conditioned  by  the  content  of  the  ideas.  Besides  these  simple 
classes  of  feelings,  one  of  these  writers  speaks  of  certain  "  mixed 
feelings,"  that  are  feelings  of  oscillation  and  change.  Under  the 
"  formal "  feelings,  or  such  as  are  dependent  on  the  form  of  the 
course  of  representation,  the  other  writer  finds  four  classes — namely, 
(a)  feelings  of  expectation  and  impatience,  (b)  of  hope,  anxiety,  sur- 
prise, and  doubt,  (c)  of  tedium,  and  (d)  refreshment  and  work — all 
according  to  the  aspect  of  the  ideas  in  time-form.  Four  kinds  of 
"  qualitative  "  feelings  are  also  distinguished — these  are  the  intel- 
lectual, the  sesthetic,  the  moral,  and  the  religious — according  as 
the  ideas  exciting  the  feelings  refer  to  truth,  beauty,  morality,  or 
religion.  But  the  foregoing  attempts  and  all  similar  attempts  at 
classifying  the  feelings  lay  a  false  emphasis  upon  the  dependence  of 
certain  feelings  on  mental  representation  ;  they  thus  overlook  all 
those  considerations  on  which  the  physiological  theories  of  feeling 
rightfully  insist. 

But,  on  the  other  hand,  the  classifications  made  under  the  in- 
fluence of  the  physiological  theory  are  even  more  unsatisfactory. 
In  their  desire  to  reduce  all  the  phenomena  of  human  feeling  under 
some  one  physical  "  law,"  so  called,  they  bring  the  higher  forms  of 

'  Das  Gefiihlsleben,  p.  44  f. 

^  Lehrbucli  d.  empir.  Psychologie,  p.  205  f. 


506  NATURE   AND   KINDS    OF   FEELING. 

feeling  into  a  mucli  closer  and  more  complete  connection  with  the 
feelings  of  sensation  than  the  facts  will  warrant.  Thus,  with  Grant 
Allen,  the  aesthetic  feelings  are  "  the  cumulative  effect  of  many 
infinitesimal  physiological  factors,"  '  which  differ  from  the  pleasures 
and  pains  of  sensation  chiefly  in  the  fact  that  the  activity  of  the 
end -organs  in  them  is  "  not  directly  connected  with  life-serving 
function  ; "  °  all  the  different  tastes  of  different  individuals,  their 
varying  "perceptions  of  beauty  and  ugliness,"  are  then  boldly 
stated  to  be  "  depending  on  the  structural  variations  of  the  nervous 
system." 

Horwicz's  more  profound  theory  as  to  the  nature  of  feeling  leads 
him  to  a  more  satisfactory  classification  of  its  forms.  The  variety 
of  feeling,  he  holds,  is  dependent  on  the  natural  organic  variety  in 
the  activities  of  the  soul.'  Thus  we  derive  (1)  the  senswoit.s  feelings, 
or  such  as  depend  on  the  different  qualities  of  the  sensations  of  the 
special  senses  and  of  common  feeling  ;  (2)  the  cesthetic  feelings,  or 
those  agreeable  or  disagreeable  forms  of  consciousness  which  cor- 
respond to  the  mental  images  of  perception  and  imagination ;  (3) 
the  intellectual  feelings,  which  correspond  to  the  theoretic  interests 
called  out  by  the  higher  forms  of  thinking  ;  (4)  the  moral  feelings, 
or  those  which  correspond  to  the  relations  of  desire  and  will.  The 
development  of  these  feelings  in  varying  relations  to  each  other 
gives  rise  to  various  mixed  or  complex  forms.  Certain  moods  and 
characteristic  affections  result  from  the  combined  tone,  color,  and 
rhythm,  of  the  simple  feelings,  and  the  strength  with  which  the 
physical  organism  reacts.  Higher  feelings,  or  "feelings  of  feel- 
ings," unfold  themselves  ;  these  are  dependent  upon  the  complex 
relations  of  society  as  organized  in  its  several  existing  forms. 

A  recent  writer  in  Mind,^  after  criticising  all  previous  attempts 
at  classification  of  the  feelings,  proposes  an  exceedingly  elaborate 
substitute  for  them  all ;  but  this  substitute  is  so  burdened  Avith 
uncouth  terminology,  is  founded  on  so  many  false  or  doubtful  psy- 
chological assumptions,  and  involves  so  many  artificial  distinctions 
and  cross  divisions,  that  it  is  little  likely  to  meet  with  general  ac- 
ceptance. 

§  9.  Another  and  insuperable  difficulty  in  the  way  of  a  strict 
classification  of  the  feelings  is  the  fact  that  they  are  actually,  and 
as  peculiar  conditions  of  consciousness,  unclassifiable.  In  other 
words,  no  principle  of  classification  can  be  suggested  which  will 
undeniably  apply  to  them  all.     For  example,  if  we  classify  them 

'  Physiological  Esthetics,  p.  42.  "^  Ibid. ,  p.  34. 

^  Psychologisclie  Analyseii,  ii.,  p.  82  f. 

*  Mercier,  July  and  October,  1884,  and  January,  1885- 


t»RIMITIVE   CHAEACTEE   OF   FEELING.  507 

into  pleasurable  or  painful,  we  indicate  in  this  way  only  a  quality 
of  tone  which  itself  constantly  varies  in  dependence  on  more  per- 
manent characteristics.  Besides,  it  is  not  easy  to  demonstrate  that 
feelings  are  never  indifferent  (neither  agreeable  or  disagreeable)  in 
tone.  If  we  classify  according  to  the  anatomical  part  or  phys- 
iological function  of  the  nervous  system  which  chiefly  gives  con-, 
ditions  to  the  feelings,  we  can  carry  our  classification  only  a  little 
way  without  resorting  to  imwarrantable  assumptions.  Indeed, 
there  are  grounds  for  supposing  that  the  feelings  are  of  central 
origin — that  is,  have  their  physiological  basis  in  those  regions  of 
the  nervous  system  that  have  thus  far  almost  wholly  eluded  sci- 
entific research.  If  we  classify  according  to  the  relation  of  each 
feeling  to  other  activities  of  the  soul  (as  Horwicz  does),  we  en- 
counter the  facts  that  sense,  will,  and  intellect,  doubtless  all  enter 
into  all  the  aqtivities  connected  with  our  developed  feeHng ;  but 
that  the  measure  of  the  degree  in  Avhich  they  are  influential  upon 
feeling  is  so  uncertain  and  changeable  as  to  render  it  unfit  to  serve 
as  a  basis  for  classification. 

No  hard  and  fixed  line  can  be  drawn  about  the  different  so-called 
classes  of  feelings.  Feeling,  with  its  color-tone  of  pain  or  pleasure, 
enters  into  all  conscious  life.  The  aesthetic  feelings  cannot  be 
separated  from  the  sensuous  ;  for  example,  the  feeling  which 
accompanies  the  sensation  of  a  musical  chord,  or  of  the  color  pur- 
ple, may  be  classed  tmder  either  head.  Nor  can  the  intellectual 
feelings  be  separated  from  the  aesthetic  ;  the  perception  of  harmony 
of  colors  and  sound  is  inseparably  connected  with  sesthetic  and 
sensuous  feeling,  and  the  latter  is  intensified  or  otherwise  modified 
under  the  intellectual  laws  of  contrast,  change,  habit,  and  higher 
association.  Even  the  feelings  which  we  call  "  moral,"  on  account 
of  their  connection  with  will  and  desire,  often  have  an  indefinite 
part  of  them  so  combined  with  feelings  located  in  the  bodily 
organism,  or  so  dependent  on  its  functions  for  their  quantity  and 
quality,  that  a  strict  separation  becomes  impossible.  Love  is 
seldom  or  never  so  purely  ideal  as  not  plainly  to  involve  in  itself 
feeling  of  sensuous  and  sesthetic  sort ;  hate  not  mixed  with  anger, 
and  so  supported  on  some  elements  of  that  physical  basis  which 
underlies  the  latter,  is  hard  to  discover  in  real  life.  All  psycho- 
logical analysis  that  would  extend  to  the  point  of  establishing  fixed 
classes  of  the  psychical  activities  is  difficult ;  but  in  the  special 
case  of  the  feelings,  the  character  of  experience  is  such  as  to  make 
strict  classification  impossible. 

Accordingly,  in  treating  of  the  feelings  from  the  physiological 
point  of  view  we  shall  content  ourselves  with  selecting  certain  ex- 


508  NATURE  AIS^D   KHSTDS   OF   FEELIXG. 

amples  from  the  cuiTent  classes  which  admit  of  being  thus  treated 
most  successfully.  Such  are,  obviously,  the  so-called  sensuous  feel- 
ings, the  so-called  common  feeling,  certain  aesthetic  feelings,  certain 
of  the  feelings  known  as  emotions  or  affections,  and  certain  feelings 
connected  with  the  functions  of  will — especially  the  feeling  of  effort. 

§  10.  All  feelings  are  characterized  by  tone,  strength,  rhythm, 
and  content.'  Their  content  is  determined  by  the  ideating  activity 
with  which  they  are  directly  connected,  or  to  which  they  are  relat- 
ed ;  and  this  content  may  be  simple,  as  is  the  case  with  the  feeling 
connected  with  the  presentation  of  a  colored  surface  (for  example, 
purple  or  green),  or  complex,  as  is  the  case  with  the  sentiments  of 
patriotism,  loyalty,  and  religious  devotion. 

Feelings,  like  all  other  mental  jDlienomena,  occur  under  time- 
form;  they  are,  in  general,  rhythmic  in  character,  and  change  in  re- 
spect to  content,  tone,  and  intensity,  with  a  movement  marked  more 
or  less  distinctly  by  the  quality  of  periodicit}'.  Their  rhythm, 
with  respect  to  content,  is,  of  course,  determined  by  the  recur- 
rence of  changes  in  the  ideating  activity  as  dependent  especially 
upon  attention  and  the  laws  of  association.  Feelings  of  sadness  or 
joy,  comfort  or  discomfort,  may  come  around  again  in  conscious- 
ness, as  it  were,  according  to  the  rhythmic  movement  of  the  sensa- 
tions which  occasion  them.  Sometimes  an  alternation  of  tone  takes 
place,  which  carries  the  mind  back  and  forth  by  the  point  of  indif- 
ference (or  hypothetical  zero-point  of  feeling)  between  agreeable 
and  disagreeable  sensations,  or  ideas  of  the  same  kind.  Thus  we 
are  sometimes  forced  to  say  that  we  do  not  know  whether  a  certain 
combination  of  colors,  or  quality  of  taste  or  smell,  is  pleasing  to  us 
or  not  ;  in  such  a  case  feeling  seems  to  move  rhythmically  back  and 
forth  between  a  slightly  pronounced  tone  of  pleasure  and  a  slightly 
pronounced  tone  of  pain. 

The  intensitij,  too,  of  feelings  rises  and  falls  alternately  in  de- 
pendence upon  the  rhythmic  movement  of  the  nervous  processes 
and  of  the  train  of  ideas.  No  feeling  is  kept  at  a  long  continu- 
ous level  with  respect  to  its  vigor  and  pitch  of  strength.  The 
law  of  quickly  alternating  exhaustion  and  repair  of  the  nervous 
elements  underlies,  to  a  large  extent,  this  rhythmic  movement  of 
the  intensity  of  the  feelings.  This  is  one  of  many  proofs  which  go 
to  show  that  the  conditions  of  the  end-organs  and  of  the  central 
organs  (comp.  p.  108  f.)  are  determinative  of  the  tone  and  strength 
of  feeling.  Even  when  we  are  strictly  attending  to  our  painful 
feeling,  the  toothache  is  not  a  perfectly  uniform  and  steady  strain  ; 
even  when  we  are  doing  our  best  to  abstract  attention  from  the 
'  Conap.  Volkmann  vou  Volkmar,  Lehrb.  d.  Psychologie,  II.,  p.  311  f. 


THE   TONE   OF   ALL   FEELING.  509 

pain,  we  succeed  only  intermittently.  But  the  course  of  the  ideas 
must  also  be  taken  into  account  as  influencing  the  rhythm  of  feel- 
ing. As  our  sensations  or  mental  images  become  more  clear  and 
vivid,  the  feelings  attached  to  them  gather  strength ;  as  the  former 
become  more  obscure  and  feeble,  the  feehngs  also  die  away  in 
consciousness. 

§  11.  The  tone  of  all  feeling  is  either  one  of  pleasure  or  of  pain 
(using  these  words  in  their  widest  possible  meaning).  The  feeling  of- 
pleasure  and  pain  is  probably  the  most  general,  most  simple,  and 
earliest  psychical  process.  That  almost  all  feelings  are  characterized 
by  some  positive  tone — or,  in  other  words,  are  not  absolutely  in- 
different to  us — there  can  be  no  question.  Is  it  agreeable  or  dis- 
agreeable, at  least  in  some  slight  degree  and  in  some  more  or  less 
indefinite  manner  ?  is  an  inquiry  which  we  can  pretty  readily  an- 
swer with  respect  to  nearly  all  our  sensations  and  ideas.  The 
question  has  been  debated,  however,  whether  this  is  necessarily  true 
of  all  our  feelings.  Is  there  any  such  thing  as  completely  "neutral" 
feeling,  or  feeling  that  is  in  no  respect  or  degree  either  agreeable 
or  disagreeable  to  us  ?  Neutral  or  indifferent  feelings  were  recog- 
nized by  Reid,  but  disputed  by  Hamilton.'  Bain  asserts  it  as  un- 
doubted that  "  we  may  feel,  and  yet  be  neither  pleased  nor  pained," 
and  that  "almost  every  pleasurable  and  j)ainful  sensation  and  emo- 
tion passes  through  a  stage  or  moment  of  indifference."^  Wundt^ 
argues,  on  theoretical  grounds,  that  pleasure  and  pain,  as  tones 
of  feeling  belonging  to  sensation,  are  conditions  which  may  be 
regarded  as  on  different  sides  of  a  zero-point,  or  point  of  indif- 
ference l^'ing  between  them.  It  does  not  follow,  however,  that, 
because  the  mind  passes  in  time  from  feeling  of  one  positive  tone 
(pleasure)  to  feeling  of  the  opposite  tone  (pain),  it  must,  therefore, 
at  some  instant  be  in  a  state  of  feeling  that  has  no  tone  and  lies 
between  the  two.  The  curve  plotted  to  represent  the  rise  and  fall 
of  feeling  is  a  material  line  ;  it  cannot  be  at  one  time  below,  and  at 
another  above,  the  abscissa-line,  Avithout  at  some  single  point  (the 
zero-point)  coinciding  with  it.  But  it  does  not  follow  that,  because 
such  a  curve  is  a  picture  of  the  phenomena  of  feeling  in  one  respect, 
it  is  so  in  all  other  respects.  The  question  whether  there  is  any 
zero-point  to  the  tone  of  feeling  can  only  be  answered  by  an  aj^peal 
to  consciousness  ;  and  this  answer,  like  all  others  given  to  similar 
appeals,  is  likely  to  contain  dubious  and  conflicting  elements.  It 
is  quite  certain  that  one  can  pass  from  a  high  state  of  pleasure  to 

'  Hamilton's  Works  of  Thomas  Reid,  p.  311.     Edinburgh,  1854. 
'  The  Emotions  and  tlie  Will,  p.  13. 
^  Phjsiolog.  Psychologie,  i. ,  p.  465  f. 


510  NATURE   AT^D   KINDS    OF   FEELING. 

one  of  intense  pain  -without  any  interpolated  neutral  feeling.  For 
example,  if  while  one  is  viewing  a  beautiful  landscape  one  is  stung 
by  hornets,  the  condition  of  quiet  massive  pleasure  may  be  converted 
into  one  of  great  physical  suffering  without  any  intervening  feel- 
ing of  indifference.  We  incline,  then,  to  agree  with  Sully '  in  af- 
firming that  every  feeling  is  either  pleasurable  or  painful  in  some 
degree.  "  We  apply  the  name  'feelings,' "  says  Lotze,"  "  exclusively 
to  states  of  pleasure  and  pain,  in  contrast  with  sensations  as  indif- 
ferent perceptions  of  a  certain  content." 

§  12.  Various  questions  may  be  raised  as  to  the  physical  appar- 
atus, the  nervous  elements  and  processes,  for  pleasurable  or  pain- 
ful feeling,  which  cannot  be  answered  satisfactorily.  Are  there 
special  nervous  elements — whether  end-organs,  or  nerve-fibres,  or 
nerve-tracts  and  centres  in  the  central  organs — which  must  be  ex- 
cited in  order  to  give  rise  to  the  feeling  of  pain  ?  If  the  apparatus 
for  feeling  is  the  same  as  that  for  the  sensations  to  Avhich  the  feel- 
ing gives  its  color-tone,  do  the  feeling  and  the  sensations  imply 
different  processes  in  these  same  elements  as  the  physical  basis  on 
which  they  rest?  Is  not  pleasure,  rather,  the  result  of  a  normal 
and  moderate  amount  of  process  in  these  elements  ;  and  pain  the 
result  of  a  process  in  the  same  elements  whose  amount  has  been 
increased  so  as  to  be  destructive  or  injurious  to  the  tissue  involved  ? 
Lotze  ^  raised  these  questions,  and  answered  tliem  with  the  opinion, 
somewhat  doubtfully  expressed,  that  sensation  and  feeling  are  due 
to  two  forms  of  processes  in  the  same  nervous  elements,  and  that 
there  is  no  need  of  assuming  special  oi'gans  of  feeling,  whether 
peripheral  or  central  Probably  the  prevalent  view  hitherto  has 
been,  that  the  same  apparatus  of  end-organs,  conducting  nerve- 
tracts,  and  central  areas,  which  on  moderate  excitement  produces 
the  simple  sensations  of  pressure  or  of  temperature,  or  the  more 
complex  sensations  of  tickling,  shuddering,  etc.,  produces  the  feel- 
ing of  pain  when  irritated  with  increased  intensity.  Such  a  view 
would  apparently  have  also  to  hold  that  muscular  sensations  have 
the  same  physical  apparatus  as  do  feelings  of  muscular  weariness 
or  exhaustion  ;  and,  perhaps,  that  cardialgia  and  hunger  are  due  to 
modifications  of  the  action  of  the  same  nerves  of  the  stomach.  But 
from  the  losychological  point  of  view  it  is  as  certain  that  sensations 
of  pressure  or  mere  temperature  are  unlike  the  feeling  of  pleasure 
produced  by  gentle  rubbing  or  by  comfortable  warmth,  or  the  pain 

'  Outlines  of  Psychology,  p.  449,  New  York,  1884 ;  and  comp.  Volkmann 
von  Volkmar,  Lehrb.  d.  Psychologic,  II.,  p.  311  f. 
'■'  Outlines  of  Psychology,  p.  73.     Boston,  1886. 
^  See  Mediciu.  Psychologie,  pp.  245  fE. 


PHYSICAL  APPAKATUS    OF   FEELING.  511 

that  comes  from  heavy  pressure  or  burning,  as  it  is  that  sensations 
of  light  are  unlike  those  of  musical  tone. 

Besides  the  obvious  difference  which  the  results  of  exciting  it 
have  in  consciousness,  there  are  other  and  physiological  reasons 
for  doubting  the  complete  identity  of  the  nervous  apparatus  of 
pleasurable  and  painful  feeling  with  that  of  the  sensations  with 
which  the  feeling  is  allied.  The  facts  upon  which  Schiff  and  others 
support  the  view  that  nervous  impulses  resulting  in  pain  travel  by 
more  or  less  distinct  paths  along  the  spinal  cord  have  already  been 
stated  (Part  I.,  chap.  HI.,  §  32).  The  most  recent  experiments  seem 
to  show  that  the  end-organs  of  temperature,  j)ressure,  and  pain  are 
locally  separable  in  the  different  minute  areas  of  the  skin  (Part  11., 
chap.  rV.,  §  21  f.).  Pathological  results  indicating  the  same  separa- 
tion of  the  nervous  elements  of  feeling  also  deserve  a  brief  men- 
tion. In  certain  cases  the  sensibility  of  the  skin  to  pain  is  lost  (a 
condition  called  "analgesic  "  by  Beau,  and  "  analgie  "  by  Lotze), 
while  its  sensibility  to  touch  is  not  weakened  or  is  even  increased. 
The  reverse  condition  also  sometimes  occurs.  "  Analgie,"  as  occa- 
sioned by  pathological  states  of  the  spinal  cord  due  to  lead-poison- 
ing, was  noticed  in  many  cases  by  Beau.  This  loss  of  seusibility  to 
pain  can  hardly  be  explained  by  any  change  in  the  activity  of  cer- 
tain end-organs  co?n?7io;i  both  to  touch  and  to  painful  feeling.  What 
impairment  of  function  could  possibly  result  in  destroying  the  sen- 
sitiveness to  strong  mechanical  and  thermic  excitations,  such  as 
ordinarily  occasion  great  pain,  while  the  response  by  way  of  sensa- 
tions of  touch  to  much  feebler  excitations  remains  undiminished? 

The  same  argument  would  appear  decisive  against  identifying,  lo- 
cally, the  central  nervous  processes  which  result  in  sensation  with 
those  which  result  in  feeling.  In  certain  stages  of  narcosis,  produced 
by  ether  or  chloroform,  the  patient  is  able  to  perceive  the  slightest 
contact  with  the  skin,  but  feels  no  pain  even  when  the  same  area  is 
treated  severely.  Moreover,  in  some  cases  of  tabes  dorsahs,  a  con- 
stant difference  seems  to  exist  in  the  time  at  which  the  sensations  of 
pressure  and  the  feelings  of  pain,  simultaneously  excited  at  the  end- 
organ,  arise  in  the  mind.  If  the  patient  is  pricked  with  a  needle, 
he  will  instantly  feel  the  contact,  and  the  pain  only  one  to  two 
seconds  later.'  The  case  of  the  eye,  which  responds  with  sensations 
of  light  and  color  when  the  optic  nerve  is  moderately  excited,  and 
with  the  painful  feeling  of  being  blinded  when  the  stimulus  is  in- 
creased, is   not   perfectly  clear.     For   cases   of  amaurosis   are  on 

1  See  Funke,  in  Hermann's  Handb.  d.  Physiol.,  III.,  ii.,  p.  297  f . ;  such 
phenomena  have  been  especiallj'  discussed  by  Osthoff,  Die  Verlangsamung  d. 
Schmerzempfinduug  bei  Tabes  dorsalis,  Eiiaugeu,  1874. 


512  NATURE   AJSTD   KINDS   OF   FEELING. 

record  where  the  painful  feeling  persisted  after  the  eye  had  lost  all 
power  to  distinguish  light.  It  has  been  argued,  therefore,  that 
while  the  specific  sensations  of  light  and  color  are  due  to  the  irri- 
tation of  the  optic  nerve,  the  excitement  of  feeling  indicates  a  si- 
multaneous irritation  of  part  of  the  trigeminus. 

We  are  compelled,  then,  to  confess  that  the  localizing  of  the 
nervous  apparatus,  and  the  nature  of  the  physiological  processes 
which  form  the  physical  basis  of  painful  and  pleasurable  feeHng, 
require  fiu'ther  investigation.  The  tendency  of  the  evidence,  how- 
ever, is  toward  a  theory  which  assigns  to  feeling  a  more  or  less 
separate  mechanism  of  end-organs,  conducting  nerve-tracts,  and 
central  areas  (or  at  least  of  nervous  elements  in  the  central  areas). 
But  how  such  a  theory  will  reconcile  itself  with  the  other  familiar 
facts  which  appear,  obviously,  to  make  the  tone  of  feeling  depend 
upon  the  degree  of  intensity  which  the  nervous  processes  attain,  it 
is  impossible  to  predict. 

§  13.  One  kind  of  feeling,  which  has  the  tone  of  pleasure  or  pain 
belonging  to  all  feeling,  is  undoubtedly  of  central  nervous  origin  ; 
this  is  the  so-called  sensus  communis,  or  "common  feeling."'  Such 
feeling  may  have  more  or  less  of  content  of  one  kind  or  another, 
according  to  the  state  of  perception  and  ideation  with  which  it  is 
combined.  Nervous  impulses  of  indefinite  variety  and  the  most 
manifold  peripheral  origin  are  constantly  pouring  in,  as  it  were, 
upon  the  cerebral  centres — each  one  contributing  some  element  to 
the  characteristic  tone  of  consciousness.  The  resulting  feelings  are 
modes  of  our  being  affected  which  are  not  converted  into  definite 
presentations  of  sense,  or  referred  to  a  particular  part  of  our  own 
bodies.  The  effect  of  changes  in  the  minute  blood-vessels  and 
other  capillaries  about  the  nerve-endings,  the  presence  of  impuri- 
ties in  the  blood,  the  condition  of  the  lower  cerebral  centres,  the 
action  of  the  heart  and  lungs  and  other  internal  organs,  and  the 
connection  of  the  sympathetic  with  the  cerebro-spinal  nervous  sys- 
tem, are  all  felt  in  this  way.  Moreover,  inasmuch  as  few  (if  any) 
sensations  are  without  some  tone  of  feeling,  while  many  sensations 
are  exceedingly  heterogeneous  in  their  elements,  and  not  clearly 
referred  to  the  place  of  their  origin,  a  melange,  as  it  were,  of  ob- 
scure bodily  affections  is  readily  formed. 

Sensations  in  themselves  heterogeneous  may  also  be  brought 
into  a  temporary  relation  by  the  partial  identity  of  their  source  of 
excitation,  and  of  the  nervous  connections  in  the  central  organs. 
It  is  also  always  a  very  important  question,  how  the  more  obscure 

'  Comp.  Funke,  Der  Tastsiuii  u.  d.  Gemeiiigefiihle,  in  Hermann's  Handb.  d. 
Physiol.,  III.,  ii.,  pp.  2a9  ff. 


COMPOSITION   OF   COMMON   FEELING.  513 

and  mixed  bodily  feelings  stand  related  to  the  mind's  course  of  idea- 
tion, to  attention,  association,  etc.  This  relation  often  determines 
whether  such  obscure  impressions  shall  be  definitely  objectified  or 
not ;  whether  they  shall  not  rather  run  together  in  the  dark  stream 
of  common  feeling.  Let  anyone  suspend  for  an  instant  a  train  of 
interesting  thought,  which  has  up  to  the  moment  been  interrupted 
only  by  certain  obscure  feelings  of  uneasiness,  and  such  one  will  be 
able  instantly  to  select  and  localize  in  the  cramped  chest,  or  op- 
pressed limbs,  or  tired  organs  of  special  sense,  most  of  the  sensa- 
tions whose  painful  tone  has  thus  colored  the  stream  of  common 
feeling.  Separation  from  localized  sensations  is,  then,  the  chief 
negative  characteristic  of  common  feeling.'  Undei"  its  different 
principal  forms  we  may  distinguish  different  total  results,  according 
to  the  general  relation  in  which  the  being  aware  merely  that  we  are 
affected  in  an  agreeable  or  disagreeable  manner  stands  to  the  being 
aware  of  lohat  affects  us  in  this  manner.  Thus  we  sometimes  feel 
well  or  ill,  elevated  or  depressed,  without  ability  to  assign  these 
feelings  at  all  definitely  to  the  physical  organism,  either  as  perceived 
or  imaged,  or  to  any  reason  in  the  train  of  ideas.  At  other  times 
the  general  impression  of  being  in  the  body,  for  some  greater  or  less 
amount  of  either  weal  or  woe,  is  emphatic  ;  we  feel  ill  all  over,  or 
seem  to  enjoy  the  coursing  of  the  ,blood  through  every  artery  and 
vein,  as  though  mentally  present  in  the  extended  tissues. 

§  14.  According  to  Strickei',"  information  derived  from  the  pe- 
ripheral nerves  consists  of  either  sensations  or  feelings  ;  the  latter 
implies  self-reference,  which  may  be  of  two  kinds.  If  this  reference 
extends  to  the  whole  sensorium,  and  so  to  the  whole  organism,  the 
feelings  are  called  "common"  or  "collective;"  under  certain  cir- 
cumstances they  appear  as  fixing  the  mood  of  our  consciousness. 
Some  of  the  organs,  in  their  sound  condition,  have  no  organic  feel- 
ings ;  others  of  them  undoubtedly  largely  determine  the  character 
of  our  common  feeling  by  their  condition,  tension,  action,  etc.  If, 
now,  we  extend  the  sensations  of  touch  so  as  to  include  all  the  ob- 
scurely localized  organic  and  muscular  sensations,  we  feel  the  neces- 
sity of  distinguishing  such  sensations  from  what  we  have  called 
the  "common  feehng." 

One  characteristic  which  the  sensations  have  as  sensations,  strictly 
speaking,  concerns  the  method  of  their  excitation.  In  general,  the 
stimulus  must  affect  the  nerves  through  the  specific  end-organs  of 
sense,  in  order  to  give  rise  to  a  proper  sensation.  E.  H.  Weber 
sought  to  prove  that,  whenever  nerves  are  irritated,  not  through  the 

'  Comp.  Lotze,  Medicin.  Psycliologie,  p.  278  f. 
^  Studien  iiber  d.  Bewusstseiii,  p.  17  f.     Wien,  1879, 
33 


514  NATURE   AND   KINDS   OF   FEELING. 

end-organs,  btit  along  the  trunk,  the  irritation  gives  rise  to  feelings 
of  pain  instead  of  sensations.  One  experiment  for  this  purpose 
consisted  in  dipping  the  point  of  the  elbow  into  ice-cold  water  ; 
when  the  sensation  of  cold  is  at  once  located  in  the  skin,  and  the 
feeling  of  pain  arises  as  soon  as  the  stimulus  has  penetrated  to  the 
trunk  of  the  nerve  lying  beneath.  But  other  experiences  seem  to 
show  that  tones  of  common  feeling  may  be  indirectly  excited,  which 
are  characterized  by  the  massing  of  a  great  number  of  minute  and 
obscurely  localized  sensations  of  touch.  For  example,  the  prick  of 
a  needle  is  felt  at  a  given  j^oint  as  a  circumscribed  pain.  The  tick- 
ling from  a  feather,  confined  to  a  small  surface,  may  be  regarded 
as  consisting  of  complex  sensations  of  light  pressiu'e,  with  no  fixed 
locality  for  each  one,  but  localized  in  general  at  about  such  a  spot. 
But  the  tickling  may  be  continued  until  a  general  tone  of  painful 
feeling  is  developed,  which  quite  overwhelms  all  localized  sensa- 
tions. These  phenomena  may  be  considered  as  agreeing  with  the 
other  phenomena  to  show  that  common  feeling  is  due  to  widely 
extended  and  complex  conditions  of  the  central  areas,  in  which 
the  results  of  a  large  number  of  separate  peripheral  stimulations 
may  unite  so  as  to  lose  all  their  individual  character,  although  each 
one  contributes  something  to  the  common  result. 

§  15.  There  are  feelings  so  connected  with  the  operation  of  the 
organs  of  sense  as  to  be  called  feelings  of  sensation.  A  certain  tone 
of  feeling  (a  third  element,  as  distinguished  from  its  specific  quality 
and  intensity)  belongs  to  most  sensations.  We  are  scarcely  war- 
ranted, however,  in  asserting  that  every  sensation,  as  such,  possesses 
some  tone  of  feeling.'  The  question  whether  every  sensation  has 
some  feeling  must  be  distinguished  from  the  question  whether  every 
feeling  is  of  either  painful  or  pleasurable  tone.  The  tone  of  the 
feeling  of  sensations  is  the  agreeable  or  disagreeable  afi'ection  of 
consciousness  which  they  often  carry,  as  inseparably  connected  with 
them.  The  particular  tone  belonging  to  any  sensation  is,  to  a  large 
extent,  dependent  on  its  intensity.  The  laws  of  this  dependence 
have  been  ingeniously  conjectured  by  Wundf  Sensations  of  mod- 
erate intensity — that  is,  of  intensity  below  the  point  at  which  the 
minimum  of  painful  feeling  begins — are  usually  pleasurable.  The 
feeling  of  pain  rises  in  intensity,  from  the  point  where  it  begins,  as 
the  intensity  of  the  stimulus  increases.  The  curves  which  represent 
the  increase  of  feeling  and  the  increase  of  sensation  by  no  means 
correspond.  It  is  assumed  by  Wundt  that  the  maximum  point  of 
pleasure  lies  about  the  so-called  "cardinal  value"  of  the  sensation, 

'  As  Wundt  does,  for  example,  Physiolog.  Psychologie,  i.,  p.  465. 
*  Physiolog.  Psychologie,  i. ,  p.  469  ;  comp.  p.  360. 


TONE   DEPENDENT   ON   INTENSITY.  515 

or  place  where  the  sensation  ceases  to  increase  in  simple  proportion 
to  the  strength  of  the  stimulus.  The  amount  of  pleasurable  feeling 
is  also  dependent  on  the  element  of  time.  It  is  thought  to  reach  a 
maximum  at  about  the  point  where  the  strength  of  sensation  is  the 
most  favorable  for  accurate  discernment  of  the  objective  stimulus. 

As  to  the  dependence  of  the  tone  of  feeling  belonging  to  a  sen- 
sation upon  the  quality  of  the  latter,  it  has  been  held  '  that  no  sen- 
sation is  ahsolately  pleasant  or  unpleasant  irrespective  of  its  in- 
tensity. Even  then,  however,  it  would  have  to  be  admitted  that 
qualitatively  different  sensations  differ  greatly  in  the  amount  which 
is  consistent  with  an  agreeable  tone  of  feeling.  It  is,  of  course, 
with  regard  to  the  organic  sensations,  and  the  special  sensations  of 
touch,  smell,  and  taste,  that  the  relation  between  tone  of  feeling 
and  the  quality  of  sensation  is  most  apparent.  Doubtless  large  al- 
lowance must  be  made  in  all  cases  for  individual  peculiarities  of 
organism,  association,  etc.  Probably,  also,  the  disagreeable  tone  of 
feeling  which  almost  universally  attaches  itself  to  certain  qualities 
of  sensation,  however  moderate  or  unobtrusive  their  intensity,  is 
largely  explicable  on  the  principle  of  heredity.  But,  taking  matters 
as  they  stand  in  present  experience,  it  is  impossible  to  maintain 
that  the  tone  of  feeling  is  not  directly  dependent  on  the  quality  of 
sensation.  This  is  a  question  upon  which  only  consciousness  can 
pronounce.  All  degrees  of  some  tastes  and  smells  are  disagreeable 
to  most  persons.  Bitter  is  a  distinctive  species  of  the  quality  of 
gustatory  sensations ;  but  the  pleasure  which  some  persons  have 
in  greater  or  less  degrees  of  it  is,  as  a  rule,  acquired.  It  is  true 
that  some  substances,  whose  odor  in  large  quantity  is  disagreeable, 
become  tolerable,  or  even  pleasant,  when  the  smell  from  them  is 
faint.  But  this  faint  smell  is  not  the  same,  but  a  distinctly  differ- 
ent quality  ;  oftentimes  it  could  not  be  immediately  recognized  as 
coming  from  the  same  substance  as  that  which  emitted  the  stronjj 
odor.  Discordant  sounds  are,  in  all  degrees  of  intensity,  naturally 
unpleasant ;  and  so  most  witnesses  would  pronounce  certain  com- 
plex sensations  of  the  skin  (as  of  creeping,  prickling,  etc.). 

§  16.  Characteristic  mixtures  of  feeling — some  of  them  scarcely 
describable — seem  to  be  attached  inseparably  to  different  kinds  of 
sensations.  This  is  obvious  when  we  consider  the  marked  difference 
in  the  wa^'-  we  are  affected  by  major  and  minor  chords,  by  succes- 
sive tones  having  different  musical  intervals  (for  example,  the  di- 
minished third,  etc.),  and  by  the  characteristic  clangs  of  different 
musical  instruments.  Writers  upon  this  part  of  musical  theory 
may  disagi'ee  as  to  the  precise  significance  of  the  violin,  clarinet, 
'  So  Wundt,  Physiolog.  Psychologic,  i.,  p.  470. 


516  HIGHER   FORMS   OF   FEELIISTG. 

cornet,  or  hautboy,  with  respect  to  the  tone  of  feeling  belonging  to 
each  ;  but  they  can  scarcely  deny  the  fact  of  a  marked  difference. 
Goethe  '  called  attention  to  the  change  in  spiritual  tone,  as  it  were, 
which  harmonizes  with  what  the  eye  sees  when  looking  upon  the 
world  through  different-colored  glasses.  Here,  again,  the  precise 
equivalent,  or  value,  in  terms  of  feeling,  which  the  different  color- 
tones  possess,  may  be  a  matter  of  dispute  ;  but  the  fact  that  the 
tones  of  feeling  change  with  the  color-tones  is  beyond  dispute. 
That  feelings  of  soberness  or  gloom  go  with  black,  of  excitement 
with  red,  of  cheerfulness  with  light  green,  of  cool  quiet  with  dark 
blue,  of  intense  sensuous  pleasure  with  saturated  j)urple,  would 
probably  be  admitted  by  most  persons.  Fewer  would  agree  to  de- 
scribing the  tone  of  feeling  belonging  to  dark  yellow  or  spectral 
orange  as  one  of  "  suppressed  excitement,"  or  to  brown  as  one  of 
"  perfectly  neutral  mood."  ° 

§  17.  The  character  of  the  disagreeable  or  painful  feeling  belong- 
ing to  different  classes  of  sensations  also  differs  with  respect  to  the 
nature  of  its  attachment  to  a  recognized  physical  basis.  Unhar- 
monious  colors  produce  in  us  a  feeling  of  mild  dissatisfaction, 
which  appears  as  almost  wholly  of  a  spiritual  kind.  Discordant 
tones  cause  more  of  physical  suffering  ;  and  disagreeable  smells 
or  tastes  create  a  widespread  sense  of  organic  discomfort.  Pains 
in  the  skin  and  interior  organs,  however,  may  take  a  character  of 
intense  bodily  anguish,  which  is  distinctive  of  no  other  qualities  of 
sensation,  and  which  is  capable  of  submerging  all  sensation,  as  such, 
in  a  flood  of  painful  feeling.^ 

§  18.  The  tone  of  sensuous  feeling  is  also  dependent  upon  the 
total  condition  of  consciousness  as  determined  by  attention,  mental 
habit,  association  of  the  feelings  among  themselves  and  with  the 
ideas,  control  of  the  will,  etc.  Such  feeling  is,  therefore,  largely  a 
secondary  element  of  experience,  which  arises  through  certain  ac- 
quired effects  of  the  sensations  as  connected  with  previous  activities 
of  the  mind.  But  concerning  the  physical  basis  of  the  feehngs,  in 
this  aspect  of  them,  we  know  nothing  whatever  ;  and  the  subject 
is  not  as  yet  one  with  which  physiological  psychology  can  success- 
fully deal. 

§  19.  The  consideration  of  the  affections  and  the  emotions,  or 
passions,  involves  at  least  three  important  particulars  :  (1)  The 
characteristic  feeling  which  distinguishes  each  ;  (2)  its  relations  to 
the  train  of  ideas,  and  the  changes  induced  by  it  in  the  ideas  ;  (3) 

1  Farbenlelire,  §  763. 

'  Comp.  Wuiidt,  Physiolog.  Psycliologie,  i.,  p.  477. 

*  Comp.  Lotze,  Outlines  of  Psychology,  p.  75 f. 


BODILY   BASIS   OF   THE   EMOTIONS.  517 

the  relations  to  the  different  bodily  organs,  and  the  reflex  effect  of 
the  changes  in  these  organs  upon  both  the  feelings  and  the  ideas. 

Each  of  the  various  affections  or  passions  is  characterized  by  a 
peculiar  feeling,  whose  tone  is  either  agreeable  or  painful,  whose 
intensity  admits  of  various  degrees,  and  whose  content  is  determined 
by  the  mental  representations  to  which  it  has  become  attached. 
Each  may  be  considered  as  having  its  rise,  psychologically,  in  some 
form  of  blind,  instinctive  impulse  that  needs  to  be  connected  with 
a  mental  image  of  the  object  which  experience  has  related  to  it  as 
corresponding  to  the  impulse.  The  germ  of  the  impulse  is  the 
natural  susceptibility  of  having  desire  awakened  by  an  appropri- 
ate stimulus,  and  the  capacity  of  forming  by  experience  the  idea 
which  corresponds  to,  or  gratifies,  the  impulse.'  Impulses  may  be 
described  as  of  two  kinds — craving,  or  attraction,  and  repulsion. 
When  the  feeling,  which  as  mere  impulse  is  blind  with  respect  to 
the  object  of  gratification,  becomes  connected  in  experience  with 
appropriate  presentations  of  sense  or  mental  pictures,  the  basis  for 
an  affection  or  passion  has  been  laid.  Thus  the  germ  of  anger  and 
hate  is  found  in  that  instinctive  impulse  of  repulsion  which  is  pro- 
duced by  all  unpleasant  resistance  of  effort,  or  painful  excitement 
of  the  nervous  system.  Sudden  and  intense  irritations — as  the 
striking  of  one's  hand  against  the  table,  the  slamming  of  a  door  in 
one's  ea]' — tend  to  arouse  the  feeliug  of  resentment.  The  affection 
of  the  child  for  the  mother  ultimately  becomes  far  more  than  the 
feeling  of  comfort  it  has  in  her  arms  or  at  her  breast ;  but  the 
former  is  cradled  and  nursed  in  the  latter.  By  varied  associations, 
impulses  of  attraction  or  of  repulsion  become  developed  into  a 
great  variety  of  affections,  emotions,  and  passions,  characteristic  of 
the  different  manifold  relations  in  which  the  sentient  soul  finds  it- 
self standing  toward  things  and  persons. 

§  20.  All  emotional  forms  of  feeling  are  accompanied  by  abrupt 
and  marked  changes  in  the  character  and  time-course  of  the  mental 
train.  Such  changes  may  be  regarded  as  standing  in  the  relation 
both  of  cause  and  of  effect  to  these  feelings.  Some  impression 
with  which  strong  feeling  has  become  associated  is  made  upon  the 
mind ;  the  result  is  a  transitory  interruption  of  the  mental  equi- 
poise. This  constitutes  in  part  the  justification  for  the  saying  that 
from  mere  feeling  to  affection  is  a  "leap."  "  As  a  rule,  the  effect  of 
any  sudden  and  surprising  impression — perception  of  some  object 
of  sense,  or  remembered  image — is  to  start  the  flow  of  emotion. 
Thus  anger,  fear,  desire,  avarice,  take  men  "off  their  guard;"  the 

'  Comp.  Wnndt,  Pliysiolog.  Psycliologie,  ii. ,  p.  33  f . 
^  Comp.  NaLlowsky,  Das  Gefiililslebeu,  etc.,  Eiuleitung. 


518  HIGHER   FGKMS   OF   FEELING. 

feelings  of  sucli  kind  that  are  started  by  a  given  mental  impression 
themselves  produce  a  confusion  of  the  mental  train.  But,  on  the 
other  hand,  this  very  disturbance  of  the  mental  train  is  itself  pro- 
ductive of  a  new  phase  of  feehng,  such  as  is  associated  with  the 
particular  ideas  that  in  confused  and  hurried  throngs  rush  into 
consciousness,  as  well  as  with  the  general  state  of  consciousness 
considered  as  one  of  haste  and  confusion.  The  physical  basis  of 
this  state  is  laid  in  the  extraordinary  condition  of  excitation  that 
exists  within  the  central  organs — the  ideo-  and  sensory-motor  cen- 
tres of  the  cerebral  hemispheres. 

§  21.  But  the  wonderful,  characteristic  effect  which  these  forms 
of  feeling  produce  upon  certain  of  the  vital  oi'gans  is  the  most 
noteworthy  peculiarity  of  all  affections,  emotions,  and  passions. 
Upon  this  point  science  has  far  less  than  we  could  wish  of  informa- 
tion reaching  beyond  the  observations  of  ordinary  experience.  Of 
such  information,  perhaps  the  most  important  concerns  the  influ- 
ence exerted  through  many  groups  of  muscles,  from  the  central 
organs,  upon  the  vaso-motor  system.  The  effect  of  shame,  fear,  or 
anger,  for  example,  upon  the  circulation  of  the  blood  is  matter  of 
common  remark.  But  some  grow  pale  and  others  red,  when  angry. 
In  1854,  K.  Wagner  investigated  the  effect  of  fear  upon  the  heart 
of  a  rabbit.  A  blow  on  the  table  near  the  animal  was  found  to 
cause  its  heart  to  stand  still  a  short  time,  and  then  resume  beating 
with  accelerated  frequency  of  stroke.  Subsequent  investigations 
have  made  obvious  the  general  effect  of  emotion  upon  the  curve  in- 
dicating the  blood-pressure.  The  effect  produced  ujDon  the  pulse 
of  a  dog  by  hearing  the  sudden  cry  of  another  dog  depends  for  its 
character  upon  whether  the  vagus  nerves  are  cut  or  not ;  but  even 
after  their  severance  a  marked  effect  of  this  kind  is  still  manifest.^ 
The  great  influence  of  these  forms  of  feeling  upon  all  the  action  of 
the  capillary  vessels,  upon  the  secretions,  etc.,  and  upon  the  respira- 
tion to  retard,  or  accelerate,  or  make  it  irregular,  is  of  the  same 
order.  That  care  and  anxiety  disturb  nutrition,  that  pain  and  sor- 
row cause  the  tears  to  flow,  that  fear  and  love  and  anger  act  upon 
the  abdominal  organs,  is  generally  recognized.  The  effect  is  some- 
times seen  in  suddenly  innervating,  and  sometimes  in  depressing, 
one  or  more  of  the  bodily  organs  ;  or  in  both  innervating  and  then 
depressing  them,  in  certain  well-recognized  cases.  On  the  basis  of 
such  facts,  Kant  suggested  a  division  of  the  affections  into  "  sthenic  " 
and  '•  asthenic."     But  many  forms  of   feeling,  as  they  run  their 

'  This  subject  has  been  investigated  by  Conty  and  Charpentier,  by  Cyon, 
Heidenhaiu,  and  others;  comp.  Exner,  in  Hermann's  Handb.  d.  Physiol.,  II., 
ii.,  p.  289f. 


BODILY   BASIS   OF   THE   EMOTIOl^S.  519 

course,  become  by  turns  sthenic  and  asthenic.  Strong  emotions  or 
passions  of  all  kinds  tend  to  destroy  the  nervous  mechanism  ;  "  the 
sthenic  kill  by  apoplexy,  the  asthenic  by  laming  the  heart."  '  Un- 
usual tension  or  relaxation  of  certain  groups  of  muscles  characterizes 
all  these  forms  of  feeling. 

The  marked  effect  which  certain  feelings  have  upon  particular 
organs  of  the  body  is  complemented  by  the  fact  that  such  organic 
effect  has  in  turn  a  marked  effect  upon  the  feelings.  The  organic  dis- 
turbances advance  step  by  step  to  form  the  physical  basis  of  a  rising 
tide  of  emotion,  and  then  fall  off  with  equal  pace  as  the  tide  of  emo- 
tion subsides.  The  organic  changes  are  not  merely  an  expression 
of  the  mental ;  they  are  its  material  cause  and  support.  Professor 
James  has  emphasized  these  facts  with  great  skill  and  in  an  inter- 
esting way.^  The  effect  upon  the  emotions  and  passions  of  putting 
the  muscles  or  other  organs  of  the  body  into  certain  conditions, 
which  is  so  remarkable  in  all  cases  of  hypnotism,  is  also  undoubted 
in  what  we  ordinarily  consider  normal  states  of  body  and  mind. 
"What  kind  of  an  emotion  of  fear  would  be  left,  if  the  feelings  nei- 
ther of  quickened  heart-beats  nor  of  shallow  breathing,  neither  of 
trembling  lips  nor  of  weakened  limbs,  neither  of  goose-flesh  nor 
of  visceral  stirrings,  were  present,  it  is  quite  impossible  to  think. 
Can  one  fancy  the  state  of  rage  and  picture  no  ebullition  of  it  in 
the  chest,  no  flushing  of  the  face,  no  dilatation  of  the  nostrils,  no 
clinching  of  the  teeth,  no  impulse  to  vigorous  action,  but  in  their 
stead  limp  muscles,  calm  breathing,  and  a  placid  face  ?  "  In  view 
of  the  foregoing  facts.  Professor  James  propounds  the  thesis,  that 
the  "  bodily  changes  follow  directly  the  perception  of  the  exciting 
fact,  and  that  our  feeling  of  the  same  changes  as  they  occur  i'8  the 
emotion."  ' 

To  neglect,  however,  that  element  of  feeling  in  ever}''  emotion 
which  is  immediately  attached  to  certain  perceptions  and  ideas 
would  be  quite  as  faulty  as  to  neglect  the  elements  which  are  only 
reflexly  blended  with  the  coniplex  of  feeling  on  account  of  the  condi- 
tion into  which  the  bodily  organs  are  thrown.  The  relation  between 
perception  and  feeling  as  a  psychological  fact  is  as  certain  and  im- 
mediate as  any  relation  can  be.  What  the  physiological  basis  for 
this  connection  is  we  do  not  know  ;  but  there  is  every  reason  to 
suppose  that  it  is,  at  the  same  time,  direct  and  of  the  nature  of  re- 
ciprocal influence  between  the  nervous  elements  and  areas  of  the 

'  Wundt,  Physiolog.  Psycliologie,  ii.,  p.  330. 
^Mind,  1884,  IX.,  p.  188  1 

^  But  since  its  author  seems  scarcely  to  have  taken  this  thesis  seriously,  it 
may  be  thought  superfluous  even  to  object  in  brief  to  it  (see  p.  205). 


520  HIGHER  FORMS   OF   FEELING. 

cerebral  centres  ;  as  well  as  indirect,  through  disturbances  pro- 
duced by  perceptions  and  ideas  within  the  remote  bodily  organs. 
The  influence  of  perception  upon  the  feelings  in  the  form  of  strong 
emotion  is  partly,  but  not  wholly,  through  the  skin,  muscles,  blood- 
vessels, organs  of  respiration,  and  viscera.  At  the  same  time  the 
characteristic  tone  which  strong  emotions  have  is  largely  colored  by 
the  sensuous  and  common  feelings  occasioned  by  the  disturbance 
of  the  organs.  When  even  the  feelings  called  aesthetic,  or  intellect- 
ual, or  ethical  and  rehgious,  are  vehemently  aroused,  an  "emo- 
tional "  equality  is  imparted  to  them  from  the  same  source. 

§  22.  By  mental  "  moods  "  is  ordinarily  understood  those  collec- 
tive conditions  of  the  mind  which  are  characterized  by  some  funda- 
mental tone,  but  without  any  special  feelings  accompanied  by  clear 
consciousness  of  their  inducing  causes.  The  principal  elements  that 
enter  into  such  moods  consist  of  ill-locahzed  sensations  arising  from 
the  internal  organs — especially  due,  perhaps,  to  disturbed  or  de- 
pressed cerebral  function ' — and  a  throng  of  half-reproduced  feel- 
ings and  ideas,  or  of  vague  single  feelings,  such  as  undefined  fore- 
boding, anxiety,  fear,  etc.  Since  these  elements  belong  to  the  some- 
what permanent  equipment  of  the  mind  (at  least  until  a  marked 
and  lasting  change  in  cerebral  condition  and  the  train  of  ideas  is 
brought  about),  their  prevalent  tone  is  characteristic  of  different 
persons ;  whereas  the  emotions  and  j^assions  run  their  course 
quickly,  and  give  a  color  to  the  personality  rather  by  the  sudden- 
ness and  frequency  with  which  this  kind  or  that,  respectively,  is 
present  in  consciousness.  But  mental  moods  also  may  be  charac- 
terized by  emotions  or  affections  of  a  low  and  lingering  tone — pale 
and  faded  specimens  of  the  type,  as  it  were. 

§  23.  Of  all  the  so-called  "higher  feelings"  (aesthetic,  intellectual, 
ethical,  religious),  it  is  only  certain  elementary  forms  of  aesthetic 
feelijig  concerning  whose  peculiar  physical  basis  we  have  any  as- 
sured information.  All  these  feelings,  however,  when  they  reach 
a  certain  degree  of  intensity,  tend  to  assume  an  emotional  character. 
They  then  come  in  part  under  the  considerations  which  have  ah'eady 
been  urged  as  applying  to  the  emotions  in  general.  A  large  portion 
of  the  strong  feelings  of  admiration  for  scientific  objects,  discoveries, 
laws,  and  personalities,  or  of  religious  fervor,  aspiration,  and  devotion, 
or  depression,  is  reflex ;  it  rests  upon  the  jDhysical  basis  of  effects  that 
are  produced  in  the  muscles  and  vital  organs — especially  the  organs 
of  secretion,  respiration,  and  circulation.  But  these  facts  do  not 
explain  or  annul  the  other  class  of  facts,  which  leads  the  judicious 
investigator  also  to  emphasize  tlie  spiritual  oiigiii  of  such  feelings 
'  Comp.  Strieker,  Studien  i'.ber  d.  Bewusstseiu,  p.  63. 


'FEELING   OF   HAEMONY   AND   EHYTHM.  521 

considered  as  complex  reactions  of  the  mind  in  view  of  the  presence 
in  consciousness  of  certain  classes  of  ideas.  So  far  as  such  spiritual 
reactions  by  way  of  feeling  have  any  even  conjectural  physical  basis 
peculiar  to  them,  this  basis  must  be  sought  for  in  the  central 
organs  of  the  nervous  sj'stem.  How  far  such  a  basis  really  exists, 
and  in  what  it  consists,  we  have  as  yet  scarcely  a  right  to  imagine — 
so  complete  is  our  ignorance. 

§  24,  The  cesthetic  feelings  arise  and  develop  chiefly  in  connec- 
tion with  presentations  of  sense,  or  with  the  remembered  or  created 
mental  images  that  represent  objects  of  sense.  In  their  elementary 
form,  therefore,  they  plainly  have  a  physiological  side  which  admits 
of  scientific  treatment — although  they  have  received  such  treatment 
far  less  than  could  be  wished.  Many  interesting  facts  and  certain 
partial  generalizations  called  law^s — having  most  application  to  the 
lower  classes  of  pleasurable  feelings  through  the  organs  of  smell, 
taste,  and  the  skin,  when  viewed  in  the  light  of  the  hypothesis  of 
evolution — are  given  in  the  work  of  Grant  Allen  on  "  Physiological 
Esthetics."  '  But  even  the  most  elementary  aesthetic  feelings  can- 
not be  considered  as  on  a  par  with  the  sensuous  feelings,  or  as  mere 
aggregates  of  such  feelings.^  The  tone  of  feeling  which  characterizes 
the  sensations  furnishes  a  material,  as  it  were,  for  genuinely  aesthetic 
feeling  ;  but  the  latter  always  implies  also  the  working  of  certain  in- 
tellectual laws,  and  a  union  of  the  simple  feelings  of  sensation  under 
time-form  and  space-form.  Esthetic  feelings,  then,  may  be  said  to 
spring  from  the  manner  of  the  combination  of  sensuous  feelings ; 
time  and  space  furnish  the  framework  in  which  they  are  arranged. 
Hearing  is  the  principal  sense  for  combining  sensuous  feehngs  so 
as  to  produce  aesthetic  feelings  under  time-form,  and  sight  under 
space-form.  The  development  of  even  the  elementary  but  genuine 
cesthetic  feelings  by  other  senses  than  the  eye  and  ear  is  extreme- 
ly limited.  The  agi'eeable  and  disagreeable  feelings  which  come 
through  sensations  of  smell,  taste,  and  touch  are  for  the  most  part 
sensuous,  rather  than  strictly  aesthetic. 

Hearing,  as  pre-eminently  the  time-sense,  has  two  forms  of  aes- 
thetic feeling — harmony  and  rhythm.  The  nature  of  the  complex 
sensations  which  produce  the  feeling  of  consonance  and  dissonance 
has  already  been  discussed.  Harmony  is  determined  by  the  co- 
incidence of  certain  partial  tones  belonging  to  different  clangs  si- 
multaneously sounded.  The  feeling  of  harmony  is  colored  by  the 
peculiar  Avay  in  which  the  combination  of  the  clangs  occurs.  The 
princiijal  difference  of  this  sort  is  that  which  obtains  be  ween  major 

'  See  pp.  30  ff. 

^  Ou  this  point,  see  Wundt,  Pliysiolog.  Psychologie,  ii.,  p.  179  f- 


522  HIGHER  EORMS   OF   FEELING. 

chords  and  minor  chords  ;  in  the  former  the  different  clangs  are 
perceived  as  firmly  held  together  by  the  fundamental  clang,  while 
in  the  latter  the  coincident  overtone  performs  the  same  office  less 
obviously.  The  one  is  jDroductive  of  agreeable  aesthetic  feeling 
satisfied  ;  the  other  of  such  feeling  left  unsatisfied — a  feeling  of 
longing.  When,  then,  the  one  form  of  feeling  becomes  very  intense, 
it  may  involve  the  pain  of  over-excitement ;  the  other,  when  inten- 
sified, stirs  a  kind  of  agreeable  pain  of  nnrest.  In  musical  time  it  is 
the  periodic  nature  of  the  excitation,  with  a  change  in  the  individ- 
ual presentations  of  sense,  which  produces  the  pleasurable  sesthetic 
feeling. 

Two  or  three  regularly  recurring  impressions,  having  the  same 
or  a  different  content  of  musical  sound,  are  combined  into  a 
series  ;  certain  members  among  the  whole  number  are  then  ac- 
centuated, in  order  to  form  the  different  series  that  constitute  the 
various  kinds  of  musical  time.  All  musical  time,  fundamentally 
considered  as  respects  its  rhythm,  is  either  two-time  or  three-time. 
The  difference  in  the  feelings  which  respond  to  these  two  classes  of 
musical  rhythm  is  obvious  in  a  pronounced  form,  in  the  funeral 
march,  on  the  one  hand,  and  the  waltz,  on  the  other.  In  general,  it 
is  the  harmony  of  music  which  gives  du'ection  to  its  feeling,  and 
the  rhythm  which  determines  the  rise  and  fall  of  feeling.  Thus 
waves  of  different  kinds  of  feeling  are  made  by  music  to  pass  over 
the  soul.' 

The  elementary  aesthetic  feelings  which  come  through  sight  lead 
to  the  consideration  of  the  aesthetic  effect  of  visual  form.  Such  ef- 
fect can  be  considered  only  very  imperfectly  from  the  physiological 
point  of  view.  In  one  important  particular,  however,  pleasurable 
sesthetic  feeling  is  directly  dependent  upon  the  combination  of  the 
sensations,  with  their  accompanying  tone  of  feeling,  under  the  laws 
of  the  mechanism  of  vision  with  both  eyes  in  motion.  Beautiful 
form  is  detei-mined  by  the  course  of  the  limiting  lines  ;  and  limit- 
ing lines,  in  order  to  have  the  effect  of  arousing  agreeable  aesthetic 
feeling,  must  accommodate  themselves  to  the  physiological  and  psy- 
cho-physical necessities  of  the  eye  when  in  motion.  These  neces- 
sities thus  determine  both  the  direction  and  the  extent  of  the  limit- 
ing lines.  Lines  of  slight  curvature,  not  too  far  continued  in  one 
direction,  best  compl}'  with  such  necessities.  Lines  of  very  sharp 
cui-vature,  or  lines  continued  too  long  in  one  direction,  do  not  pro- 
duce a  pleasing  sesthetic  effect.  So  also  must  the  main  lines  of  a 
building  lie  in  horizontal  or  vertical  directions,  preferably  in  the 

'  For  a  treatment  of  sestlietic  feeling  in  music,  comp.  Wundt,  Phjsiolog. 
Psychologie,  ii.,  pp.  180  ff. 


THE   GOLDEN   DIAMETEE.  523 

former  direction.  But  long  oblique  lines — for  example,  from  a 
lower  rigiit-hand  to  an  upper  left-hand  corner  of  a  building — are 
scarcely  tolerable.  The  ease  with  which  the  eye  sweeps  the  lines, 
in  order  to  make  that  synthesis  of  successive  similar  presentations 
of  sense  in  which  every  perception  of  a  line  consists,  is  plainly  a 
determioing  factor  in  all  these  cases. 

The  aesthetic  effect  of  visual  form  is  also  determined  by  the  way 
in  which  the  form  is  constructed,  through  repeating  similar  or  un- 
like simple  shajDes  and  combining  them  into  a  totality.  By  this 
means  a  feeling  of  pleasure  akin  to  the  feeling  of  musical  rhythm 
is  excited  by  the  successive  impressions  which  occui"  periodically  as 
the  eye,  with  a  nearly  uniform  movement,  sweeps  the  entire  field. 
In  horizontal  directions,  the  law  for  the  arrangement  of  the  parts  is 
that  of  symmetry  of  the  simple  parts  ;  in  vertical,  rather  the  law 
of  asymmetry.  Certain  proportions  between  the  connected  parts, 
and  between  the  whole  and  the  parts,  are  favorable  to  the  develop- 
ment of  aesthetic  feeling.  The  rule,  that  the  whole  of  a  presentation 
of  sight  shall  be  to  the  larger  part  as  the  larger  part  is  to  the  small- 
er part,  has  been  called  "  the  golden  diameter  "  (x  +  1  :  x  :  :  x  :  1)  ; 
since  the  proportion  thus  determined  has  been  supposed  to  be  par- 
ticularly favorable  to  pleasurable  gesthetic  feeling.  Ease  of  the 
mental  apprehension  with  which  the  relations  in  proportion  of  the 
different  parts  are  presented  is  favorable  to  agreeable  aesthetic  feel- 

§  25.  But  all  the  foregoing  rules,  and  all  others  similar,  are  appli- 
cable to  the  aesthetic  feelings  of  form  rather  as  coming  under  the 
general  class  of  intellectual  feelwgs.  That  change  in  degree  or  kind 
of  activity,  recognition  of  similarity  or  contrast,  and  mental  appre- 
hension of  a  law  or  principle  as  expressed  in  the  presentations  of 
sense,  determine  the  agreeable  character  of  our  intellectual  feel- 
ings, is  recognized  by  psychologists  '  generally ;  but  as  to  the 
physical  basis  of  mental  facts  of  this  order  we  are  almost  completely 
ignorant.  It  is  not  unlikely,  however,  that  the  effects  of  monotony 
and  change  upon  the  feelings  of  an  intellectual  order  are  connected 
with  the  same  law  of  the  exhaustion  of  the  nervous  elements  as  ap- 
plied to  the  cerebral  areas  which  we  know  to  hold  good  in  other 
parts  of  the  nervous  system. 

§  26.  The  only  other  class  of  feelings  which  admit  of  considera- 
tion from  the  physiological  point  of  view  is  the  so-called  "feelings 
of  effort,  or  of  innervation."  These  feelings  are  especially  con- 
nected with  all  the  motions  of  the  body  considered  as  furnishing 

'  See  the  judicious  remarks  of  Sully,  Outlines  of  Psjchologj',  pp.  457  S. 
New  Yo:k,  1884. 


524  HIGHEE   FORMS   OF  FEELING. 

information  concerning  its  position  and  the  condition  of  tension  oi 
strain  to  which  its  parts  are  subject  ;  as  well  as  furnishing,  through 
revived  mental  images  of  such  feelings,  the  means  for  reproducing 
voluntarily  the  required  definite  modes  of  motion.  Such  feelings 
also  have  a  great  psychological  interest  on  account  of  their  obvious 
connection  with  the  development  and  consciousness  of  acts  of  will. 
The  dispute  as  to  whether  they  are  of  central  or  peripheral  origin, 
and  as  to  that  in  which  their  precise  nature  consists,  has  already 
been  alluded  to  (pp.  344  and  415). 

That  we  have  a  ' '  feeling  of  effort "  is  a  fact,  as  says  Professor 
James,'  "  consecrated  by  the  institution  of  the  word  effort,  and  its 
synonyms  exertion,  striving,  straining."  The  nervous  process  which 
occasions  this  feeling  the  great  physiologist  Miiller  ^  considered 
to  be  purely  central,  and  to  consist  in  the  discharge  from  a  motor 
centre  into  the  motor  nerves.  This  view  has  since  been  widely 
adopted  by  physiologists  ;  it  has  also  been  used — especially  by  Bain 
and  AVundt — as  an  essential  factor  in  a  theory  of  sense-perception, 
as  of  chief  importance  in  accounting  for  our  experience  of  solid  re- 
sisting objects  of  sense  and  of  whatever  belongs  to  the  inertia  of 
matter  in  general.  On  the  contrary,  it  has  been  maintained  that 
the  feeling  of  effort,  over  and  above  what  is  purely  "  moral"  (as  in 
the  effort  to  remember  to  make  a  decision,  etc.),  is  a  comjDlex  of 
afferent  sensations  "  coming  from  the  tense  muscles,  the  strained 
ligaments,  squeezed  joints,  fixed  chest,  closed  glottis,  contracted 
brow,  clinched  jaws,^  etc." 

Of  the  two  views  above  mentioned,  the  latter  has  by  far  the  most 
in  its  favor.  The  argument  from  the  consciousness  of  effort  which 
we  may  have  when  we  intensely  make  believe  use  any  limb,  but 
do  not  actually  move  it  (as,  for  example,  the  pulling  of  a  trigger 
with  the  forefinger  of  an  extended  hand),  has  been  answered  by 
Terrier.  ■*  This  observer  calls  attention  to  the  fact  that  the  feeling 
of  effort  in  such  cases  is  due  to  keeping  the  glottis  tightly  closed, 
and  actively  contracting  the  resjoiratory  muscles.  If  we  tr}',  how- 
ever, to  make  believe  exert  ourselves  without  actually  contract- 
ing the  muscles  of  the  limbs,  and  at  the  same  time  keep  breathing 
regularly,  we  shall  not  experience  the  slightest  trace  of  the  feeling 
of  effort,  no  matter  how  hard  we  try.  This  feeling,  then,  when  the 
glottis  is  closed  and  the  respiratory  muscles  are  tense,  is  due  to 
centripetal  impressions  coming  from  the  parts  thus  innervated. 

The  argument  from  the  feelings  of  effort  which  determine  our 

'  The  Feeling  of  Effort,  Anniversary  Memoirs  of  the  Boston  Soc.  of  Nat. 
Hist.,  1880,  last  monograph.  '^  Physiologie  A.  Menschen,  II.,  p.  500. 

^  See  James,  Feeling  of  Effort,  p.  4.     ^  The  Functions  of  the  Brain,  p.  222  f 


THE   FEELITSTG    OF   EFFORT.  525 

localization  of  objects  lias  been  presented  in  the  most  convincing 
way  possible  by  Helmlioltz  and  Wundt,  as  applied  to  the  case  of 
partial  paralysis  of  the  external  rectus  of  one  eye.  Inasmuch  as 
the  patient  feels  (so  von  Graefe  ^  showed)  that  he  has  moved  his 
lame  eye  much  farther  than  he  really  has,  the  inference  is  drawn 
that  this  exaggerated  feeling  of  effort  must  originate  in  central 
motor  impulses  Avhich  have  followed  ujDon  the  fiat  of  the  will.  This 
argument,  however,  neglects  to  notice  what  goes  on  in  the  other 
and  sound  eye.  Since  this  eye,  unlike  the  lame  one,  continues  its 
motion  until  the  limit  of  motion  and  its  corresponding  condition 
of  peripheral  strain  is  reached  ;  and  since,  as  Hering  "  has  shown 
(comp.  what  has  already  been  said,  p.  439  f .),  both  eyes  are  innervated 
by  one  common  act,  and  their  motor  apparatus  is  to  be  regarded  as 
functioning  as  one  organ — the  feeling  of  effort  is  probably  due  to 
afferent  sensory  impulses  occasioned  by  the  condition  of  the  sound 
eye  as  well  as  of  the  other  eye.^  Moreover,  the  more  critically  we 
examine  those  cases  which  occasionally  occur,  where,  on  account 
of  paralysis  causing  anaesthesia,  the  sense  of  position  of  the  limbs 
is  impaired  or  lost,  the  more  conclusive  does  the  evidence  appear 
against  the  theory  that  the  feeling  of  effort  is  of  purely  central  ori- 
gin. For,  in  general,  it  seems  that,  while  the  power  of  voluntary 
motion  remains  unimpaired,  if  the  sensations  which  have  a  pe- 
ripheral origin  are  impaired  or  lost,  the  various  feelings  of  effort 
connected  with  the  accomplishment  of  a  given  amount  of  motion, 
or  with  the  act  of  holding  any  member  of  the  body  against  the  pull 
of  gravity,  are  disturbed  or  disappear.''  As  far  as  the  evidence  re- 
garding this  obscure  subject  reaches  at  present,  the  feeling  of  effort 

'  Handb.  d.  gesammten  Augenlieilkunde,  VI.,  p.  18  f. 

'  See  Hermann's  Handb.  d.  Physiol.,  III.,  i.,  pp.  512  f.  and  520  f. 

2  See  James,  Feeling  of  Effort,  p.  10  f . 

■*  See  a  recent  paper  on  "  Le  Sens  mnscnlaire  et  les  Sensations  musculaires,'' 
by  E.  Gley,  in  the  Revue  Philosophique,  1885,  pp.  601  ff.  In  this  paper  the 
results  of  the  investigations  of  M.  Maguin,  conducted  upon  paralytics  in  the 
Hopital  de  la  Pitie  (Comptes  rendus,  Mars  1884,  i. ),  are  appealed  to  as  con- 
firmatory of  the  view  that  the  stretching  and  rubbing  of  skin,  ligaments,  joints, 
etc.,  enter  into  our  so-called  feelings  of  effort.  M.  Demeaux  has  reported  the 
case  of  a  woman  who  could  move  her  limbs,  but  could  not  tell  whether  they 
were  moved,  or  in  what  direction,  or  how  far.  Xo  fewer  than  three  similar 
cases  were  reported  by  French  physicians  in  the  year  1885.  The  same  view 
of  the  complex  peripheral  origin  of  the  feeling  of  effort  seems  also  to  be  fa- 
vored by  the  experiments  of  M.  Bloch,  who  tried  placing  his  hands  symmet- 
rically on  a  screen  with  two  leaves  covered  with  paper,  divided  into  small 
squares,  under  the  guidance  of  the  so-called  muscular  sense.  The  testimony 
of  persons  who  have  lost  their  limbs,  as  to  whether  they  can  produce  any  feel- 
ing of  effort  by  the  fiat  of  will  to  move  the  lost  member,  is  conflicting.     In  all 


526  IN'ATURE   OF   THE   BODILY   MOTIONS. 

must  be  held  to  be  complex,  and  so  is  akin  to  other  forms  of  com' 
mon  feeling  ;  its  constituent  elements  are  the  various  obscurely  lo- 
calized sensations,  with  their  characteristic  tones  of  feeling,  which 
arise  in  the  condition  of  skin,  muscles,  ligaments,  joints,  etc. 

§  27.  The  feeling  of  effort  is  closely  connected  in  experience 
with  the  changing  positions  of  the  members  of  the  body,  and  its 
consideration  therefore  fitly  introduces  that  of  the  bodily  motions. 
As  concerns  their  relation  to  the  phenomena  of  mind,  these  motions 
may  be  divided  into  two  great  classes' — namely,  such  as  are  not 
demonstrably  connected  with  antecedent  changes  in  the  states  of 
consciousness,  and  such  as,  in  addition  to  their  physical  condi- 
tions and  causes,  require  that  their  explanation  should  take  account 
also  of  preceding  states  of  consciousness.  The  former  are  to  be 
regarded  purely  as  activities  of  the  physical  mechanism,^  and  are 
either  automatic  or  reflex.  Automatic  motions  are  such  as,  with- 
out any  corresponding  idea  or  fiat  of  will,  originate  from  inner 
excitations  of  the  central  nervous  system  ;  the  rejiex  are  those  in 
which  the  central  excitations  resulting  in  motion  are  traceable  to 
the  action  of  sensory  nerves  which  have  been  peripherally  excited. 
It  is  extremely  difficult  to  distinguish  between  automatic  and  reflex 
motions,  and  scarcely  less  so  to  distinguish  between  the  automatic 
and  the  impulsive.  Indeed,  while  it  is  true,  on  the  one  hand,  that 
reflex  and  centrally  co-ordinated  movements  form  the  basis  upon 
which  all  our  developed  life  of  voluntary  motion  takes  place,  it  is 
also  true,  on  the  other  hand,  that  the  more  complex  co-ordinated 
movements  are  themselves  originally  voluntary  motions  which  have, 
as  it  were,  become  habitual  and  so  dropped  out  of  consciousness 
into  a  statical  and  mechanical  way  of  taking  place.  The  sensations 
and  ideas  of  motions  may  then  be  said  to  tend  constantly  in  two 
directions — either  toward  consciousness  or  out  of  it.  It  is  by 
means  of  these  processes  in  two  directions  that  all  our  learning  of 
complicated  movements  of  the  body,  of  feats  of  dexterity  and  skill 
— learning  to  handle  tools,  to  play  on  musical  instruments,  etc. — 
takes  place.     The  interest  which  psychology  has  in  the  automatic 

such  cases,  however,  it  is  probable  that  the  alleged  feeling  of  effort  is  'to  be 
looked  for  in  the  actual  condition  of  strain  into  which  some  existing  part 
of  the  body  is  thrown — especially  the  apparatus  of  respiration  (see  Bastian, 
British  Med.  Journal,  1869,  p.  461). 

'  Comp.  Wundt,  Physiolog.  Psychologie,  ii  ,  p.  400  f . ;  and  Lotze,  Medicin. 
Fsychologie,  p.  286  f. 

■■'  The  mechanism  of  the  bodily  motions  has  already  been  treated  at  length : 
for  the  nerve-muscle  machine,  see  pp.  lU4ff. ;  for  reflex  motion,  see  pp.  182ff  ', 
for  automatic  motion,  see  pp  147  fE. ;  for  the  sensory-motor  areas  of  the  cere* 
brum,  see  p.  267  fE. 


BASIS   OF   VOLUNTAKY   MOVEMEN"T.  527 

and  reflex  motions  is  chiefly  on  account  of  their  relations  to  motions 
which  ai^e  actually  preceded  by  conscious  ideation  and  voHtion. 

§  28.  Such  motions  of  the  body  as  require  us  to  take  account  of 
antecedent  or  accompanying  states  of  consciousness,  in  addition  to 
the  connections  of  the  physical  mechanism,  are  either  impulsive  or 
voluntarj'.  But  this  distinction  is  one  which  admits  of  such  a  great 
variety  of  degrees  shading  into  each  other,  that,  although  it  is 
valid  and  necessary  in  principle,  it  cannot  be  carried  through  in 
practice  with  any  considerable  precision.  By  an  impulsive  motion 
we  understand  a  motion  which,  without  a  conscious  fiat  of  will,  fol- 
lows upon  certain  ideas  and  excited  states  of  feeling.  The  motif 
of  the  impulsive  movement  lies,  then,  in  some  form  of  feeling  that 
determines  will  one  way  without  any  proper  choice.  If  we  speak 
of  such  motions  as  volitional  or  voluntary,  it  must  be  understood 
tliat  we  are  refei-ring  to  activities  of  will  of  a  lower  order,  psycho- 
logically considered,  than  those  which  come  into  play  in  all  cases  of 
conscious  choice.  Impulsive  motions  are,  in  general,  more  quickly 
accomplished  than  are  voluntary  motions;  because  the  reaction- 
time  is  shortened  through  will-time  proper  having  been  dropped 
out  (comp.  chap.  VIII.;  §  19  f.). 

§  29.  All  voluntary  movement  has  its  basis  laid,  so  to  speak,  in 
impulsive  movement,  and  in  the  reactionary  effect  which  the  latter 
has  upon  the  conditions  of  reflex  and  automatic  bodily  activities. 
As  laid  in  this  basis,  voluntary  motions  imply  a  development  of  in- 
telligence and  will.  The  infant  finds  itself  equipped  with  a  bod- 
ily mechanism  which,  under  the  influence  of  external  and  internal 
stimuli,  is  kept  excited  to  unceasing  activity  of  the  peripheral  mem- 
bers. This  activity  results  in  certain  sensations  and  feelings  of 
effort,  in  the  manner  previously  described.  The  tone  of  these  states 
of  consciousness  is  one  of  either  pleasure  or  discomfort,  under 
those  laws  of  relation  between  the  nervous  mechanism  and  conscious 
feeling  which  can  be  only  imperfectly  stated  ;  and  which,  when 
most  perfectly  stated,  can  only  be  accepted  as  ultimate  matters  of 
fact.  By  nature  the  nervous  mechanism  is  so  arranged  that  certain 
other  bodil}'  motions  of  peripheral  origin  are  started  on  occasion  of 
the  pleasant  or  painful  feeling,  and  these  motions  are  adapted  to 
enhance  the  feeling  if  pleasant  and  to  relieve  it  if  painful.  The 
feelings  thus  become  further  connected  with  the  ideas  of  the  mo- 
tions that  modify  them  ;  yet  the  mechanism  of  the  motions  is  not 
to  be  regarded  as  originally  dependent  upon  the  ideas,  but  rather 
as  originated  in  connection  with  the  feelings  of  pleasure  or  discom- 
fort and  naturally  adapted  to  secure  an  increase  of  the  one  or  a 
diminution  of  the  other. 


528  NATURE   OF   THE   BODILY   MOTIOISS. 

The  voluntary  naovemeBts  of  the  body,  accordingly,  presuppose 
the  impulsive,  and  yet  they  reach  far  back  into  the  obscurity  of  the 
earlier  development  of  consciousness.  Strictly  speaking,  they  imply 
the  presence  in  consciousness  of  two  or  more  different  or  conflict- 
ing ideas  of  motion,  one  of  which  rather  than  the  others  is  realized 
as  a  sequence  of  an  act  of  conscious  choice.  They  imply,  then — 
as  has  already  been  said — a  considerable  development  of  the  men- 
tal activities  of  ideation  and  volition.  Moreover,  those  movements 
which  are  ordinarily  called  voluntary  ai'e  really  so  only  with  respect  to 
certain  of  their  elements ;  they  all  also  contain  elements  which  must 
be  classed  as  reflex,  centrally  co-ordinated,  and  impulsive.  The  term 
"voluntary  "  fitly  lays  the  emphasis  upon  the  conscious  act  of  choice  ; 
and  this,  in  turn,  implies  ideas  of  various  possible  forms  of  bodily 
motion  gained  by  previous  experience  with  the  correlated  states  of 
conscious  feeling  and  conditions  of  the  body  as  giving  rise  to  or 
modifying  these  states. 

The  voluntary  motions,  therefore,  constitute  the  highest  class  of 
motions,  both  because  their  conditions  include  all  those  which  be- 
long to  the  other  classes,  and  other  conditions  besides,  and  also 
because  of  their  more  direct  connection  with  the  development  of 
certain  mental  phenomena  of  supreme  psychological  interest  and  im- 
portance. To  move  any  part  of  the  body  voluntarily  requires  the  fol- 
lowing particulars  :  (1)  The  possession  of  an  educated  reflex-motor 
mechanism,  under  the  control  of  those  higher  cerebi'al  centres  which 
are  :nost  immediately  connected  with  the  phenomena  of  conscious- 
ness ;  (2)  certain  motifs  in  the  form  of  conscious  feelings  that  have 
a  tone  of  pleasure  or  pain,  and  so  impel  the  mind  to  secure  such 
bodily  conditions  as  will  continue  or  increase  the  one  and  discon- 
tinue or  diminish  tlie  other  ;  (3)  ideas  of  motions  and  positions  of 
the  bodily  members,  which  previoiis  experience  has  taught  us  an- 
swer more  or  less  j^erfectly  to  the  motifs  of  conscious  feeling  ;  (4)  a 
conscious  _/ia^  of  will,  settling  the  question,  as  it  were,  which  of  these 
ideas  shall  be  realized  in  the  motions  achieved  and  positions  attained 
by  these  members  ;  (5)  a  central  nervous  mechanism,  which  serves 
as  the  organ  of  relation  between  this  act  of  will  and  the  discharge  of 
the  requisite  motor  impulses  along  their  nerve-tracts  to  the  groups 
of  muscles  peripherally  situated. 

As  to  the  first  and  second  of  the  foregoing  particulars,  nothing 
further  need  be  said  ;  and  as  to  the  definite  nature  of  the  physical 
basis  which  underlies  the  connection  of  ideas  of  motion,  fiat  of  will 
adopting  one  idea,  and  the  starting  oiitward  of  the  right  motor  im- 
pulses, our  ignorance  is  almost  complete.  It  is  more  than  probable 
that  we  cannot  will  the  movement  of  muscles,  of  the  results  of  whose 


WILL   AS   A   PSYCHICAL   ACTIVITY.  529 

actual  movement  in  the  induced  motion  of  the  limbs  we  have  ac- 
quired no  idea  from  previous  experience.  The  mental  images  of  the 
various  feelings  of  motion  and  position  which  have  been  acquired 
in  the  past  are  our  guides  in  realizing  again  the  same  motions  and 
positions  of  the  limbs.  To  say  I  will,  refers  to  the  future.  But  we 
can  never  "  will"  motion  in  general — motion,  that  is,  of  no  partic- 
ular members  of  the  body,  and  without  specific  quality,  direction, 
and  velocity  of  the  motion.  That  certain  nervous  processes  in  the 
central  organs  form  a  ph3'sical  basis  for  the  mental  phenomena  of 
ideation  and  fiat  of  will  there  is  sufficient  ground  for  believing. 
The  phenomena  of  reaction-time  show  that  interrelated  cerebral 
activities  of  more  and  more  complicated  sort  are  implied  in  the  in- 
creased time  required  for  completing  the  mental  actions  of  repre- 
sentation and  choice  between  two  members  of  an  alternative.  It 
would  be  a  great  mistake,  however,  to  regard  the  mind  as  having 
before  it  the  cerebral  machinery,  all  nicely  laid  out,  together  with 
the  acquired  art  of  selecting  and  touching  the  right  nervous  ele- 
ments in  order  to  produce  the  desired  motion,  as  a  skilful  player  of 
the  piano  handles  his  key-board.  The  mind  has  no  native  or  ac- 
quired knowledge  of  the  different  ideo-motor  areas  of  the  cerebrum. 
Even  less  can  we  regard  the  mind,  acting  under  the  form  of  energy 
of  will,  as  bringing  some  stress  to  bear  upon  the  right  centi'es  of 
the  brain,  and  thus  setting  them  in  motion  by  laying  its  own  hand 
to  them,  as  it  were.  The  activity  of  which  we  are  directly  con- 
scious under  the  term  "to  will  "  is  a  purely  psychical  activity  ;  it 
is  marked  by  no  transition  of  force  from  the  spiritual  realm  to  the 
material  molecules  of  the  nervous  structure.  The  feeling  of  effort, 
which  seems  to  us  to  accompanj'  the  active  putting-forth  of  will,  is 
itself  a  resultant  of  mixed  sensations  that  have  a  peripheral  origin. 
The  whole  description  of  such  transactions  of  voluntary  motion  as 
are  constantly  occurring — for  example,  when  we  rise  to  close  the  win- 
dow, take  the  pen  in  hand  to  write,  etc. — is  as  follows  :  We  desire 
to  have  something  done  ;  mental  images  of  the  bodily  motions  and 
positions  involved  in  this  doing  arise  in  the  mind ;  the  fiat  of  will 
goes  forth  adopting  one  of  them,  and  u-illing  it,  as  we  say  ;  an  or- 
der of  nature  which  has  correlated  this  fiat  with  certain  cerebral 
changes,  but  of  which  we  know  nothing  whatever  directly,  and  little 
through  the  most  searching  investigations  of  science,  runs  its  coiu'se, 
and  the  transaction  which  we  have  ideated  and  willed  tnkes  place.' 
The  mind  can  represent  the  ideas  in  consciousness,  and  issue  the  fiat 
of  will ;  it  can  do  nothing  more.     Science  can  oul}^  conjecture  at 

'  This  view  of  the  subject  has  been  repeatedly  enforced  by  Lotze  ;  see,  espe- 
cially, the  Microcosmus,  i. ,  pp.  283  fE.     Edinburgh,  1885. 
34 


530  NATURE   OF   BODILY   MOTIONS. 

present  what  then  takes  place.  It  is  to  its  advancing  theory  of 
nerve-physiology,'  and  of  the  localization  of  cerebral  function,'^  that 
we  must  look  for  more  light  on  the  question —  What  happens  in  the 
brain  ivhen  the  fiat  of  will  issues  in  consciousness  ? 

§  30.  Reflection  on  the  foregoing  principles  makes  it  obvious 
that  the  different  concrete  motions  of  ordinary  experience  cannot 
be  assigned  with  confidence  to  this  or  that  class  exclusively.  In 
the  life  of  the  infant  we  can  trace  a  general  progress  from  an 
almost  exclusive  predominance  of  reflex  and  automatic  motions, 
through  the  impulsive,  to  more  and  more  of  the  voluntary.  But 
even  in  the  infant's  case  no  hard  and  fixed  lines  can  be  drawn  be- 
tween the  various  classes  of  motions.  It  is  impossible  to  say  how 
much  of  the  constant  movement  of  its  legs  and  arms  is  reflex,  how 
much  automatic.  It  is  also  doubtful  how  far  and  how  long  the 
winking  of  the  eyes,  the  grimaces  of  face  accompanying  the  stimu- 
lating of  the  tongue,  the  starting  at  sound,  etc.,  are  reflex  rather 
than  impulsive.  The  same  thing  is  true  of  its  earlier  cryings,  mi- 
metic and  imitative  movements,  and  various  ways  of  thrusting  out 
and  drawing  in  its  limbs  in  a  purposeful  way.  Nor  can  the  earlier 
voluntary  motions  be  confidently  distinguished  from  the  impulsive. 

This  line  of  inquiry  is  especially  interesting  with  respect  to  the 
beginnings  of  articulate  speech.  A  tolerably  regular  transition 
from  the  sounds  in  which  the  earliest  emotions  express  themselves 
to  the  deliberate  formation  of  words  and  sentences  makes  it  impos- 
sible to  tell  precisely  when  the  child  assumes  control  of  its  organs 
of  speech.  But  our  difficulties  with  the  unclassifiable  phenomena 
of  infantile  life  do  not  seem  so  strange  when  we  reflect  upon  the 
fact  that  the  complicated  bodily  motions  of  adult  life  partake  at 
one  and  the  same  time  of  all  the  four  above-mentioned  classes  ; 
and  that  precisely  the  same  motions  may  pass  rapidly  out  of  one 
class  into  another.  The  person,  for  example,  who  is  balancing  with 
a  pole  on  a  tight-rope,  or  dancing  to  music,  is  involved  at  once  in 
motions  which  correspond  to  all  four  of  these  principal  classes  ; 
and  a  quick  change  in  circumstances  may  make  any  one  of  the 
four  more  prominent  than  another.  So  perfectly  may  the  nervous 
mechanism  be  trained  to  its  work  that  it  may  continue  to  play  the 
violin  in  an  orchestra  after  the  player  has  lost  consciousness.  Yet 
the  rise  and  fall  of  feeling  usually  serves  as  a  guide  to  the  artist,  so 
that  impulsively  his  bowing  draws  nearer  the  bridge  in  the  cres- 
cendo, and  nearer  the  key-board  in  the  diminuendo,  passages.  If  he 
plays  false  or  out  of  time,  the  sight  of  the  leader's  baton,  or  his  own 

'  Comp.  Part  I.,  chaps.  III.  and  VII. 
Comp.  Part  II.,  chaps.  I.  and  II. 


'  MOTION   AS   EXPRESSIVE   OF   FEELTNG.  531 

sensations,  may  decide  him  to  the  fiat  of  will  which  changes  the 
spacing  with  the  left  hand  oi'  the  bowing  with  the  right  arm. 

§  31.  The  origin  and  nature  of  those  motions  of  the  body  that 
are  specifically  expressive  of  certain  ideas  and  feelings  constitutes 
one  of  the  most  interesting  fields  of  inquiry.  It  is  a  field,  however, 
in  which  comparative  psychology,  by  dealing  with  the  facts  of  ani- 
mal life  under  the  theory  of  evolution,  is  particularly  successful ; 
whereas  Physiological  Psychology,  strictly  speaking,  has  little  to 
communicate.  This  little  has  been  summarized  by  Wundt '  under 
three  general  statements  or  principles — namely,  the  princi^Dle  of 
the  direct  alteration  of  innervation,  the  principle  of  the  association 
of  analogous  sensations,  and  the  principle  of  the  relation  of  motion 
to  the  presentations  of  sense.  Under  the  principle  of  the  direct 
alteration  of  innervation  are  placed  those  facts  which  show  that 
strong  emotions  exercise  an  immediate  reaction  on  the  central  parts 
of  motor  innervation  in  such  a  way  that  many  groups  of  muscles  are 
lamed  at  once,  and  others  are  excited  to  tense  action  followed  by  ex- 
haustion. Hence  the  tremblings  of  limbs  and  organs  of  speech,  the 
changes  in  the  blood-vessels  and  capillaries  connected  with  secre- 
tion, the  paling  of  fear,  the  reddening  of  anger  and  shame,  the 
erect  hairs  under  the  influence  of  terror,  etc.  The  princi]ple  of  tbe 
association  of  analogous  sensations  emphasizes  such  facts  as  imply 
that  sensations  having  a  common  tone  of  feeling  are  most  easily 
combined,  and  then  operate  mutually  to  strengthen  each  other. 
Under  this  principle  come  the  mimetic  movements  of  mouth  and 
nose  expressive  of  disgust  or  pleasant  taste,  the  postui'ings  of  the 
tongue  in  connection  with  ideas  of  sweet  or  bitter,  the  expressive 
condition  of  the  muscles  due  to  certain  sensations  of  the  skin,  etc. 
The  consideration  of  the  third  principle — that  of  the  relation  of 
motion  to  the  presentations  of  sense — brings  before  us  the  question 
of  the  origin  of  all  the  gestures  and  pantomimic  action  not  account- 
ed for  under  the  two  foregoing  principles.  Gestures  with  eyes  and 
head  and  limbs,  indicative  of  extension  and  relations  in  space  ;  the 
arrangement  of  the  muscles  and  skin  of  the  countenance,  and  the 
motions  of  the  eyes  under  the  influence  of  care,  expectation,  and 
reflection  ;  the  angles  of  the  lines  about  the  mouth  and  the  open- 
ings of  mouth  and  nostrils  when  weeping  or  laughing,  etc.,  all  be- 
long under  this  principle.  But  the  physiology  and  psychology  of 
the  comic,  the  science  of  physiognomy,  and  of  articulation  in  expres- 
sive speech,  although  properly  coming  in  this  connection,  lead  into 
descriptive  anatomy  and  the  theory  of  aesthetics  much  beyond  the 
limits  necessarily  set  to  our  investigation. 

'  Physiolog.  Psycliologie,  ii. ,  chap.  20. 


CHAPTER   X. 

PHYSICAL    BASIS    OF    THE    HIGHER    FACULTIES. 

§  1.  An  ardent  advocate  of  "  Psychology  without  a  soul "  affirms ' 
that  "the  study  of  abstract  concepts  (time,  number,  etc.)  falls  out- 
side the  province  of  physiological  psychology,  and  has  been  made 
incidentally  only."  To  be  sure,  this  author  has  previously '  antici- 
pated the  time  when  the  science  of  mind  will  succeed  "  in  deter- 
mining the  (physical)  conditions  of  all  mental  action,  of  whatever 
sort,  as  Avell  of  pure  thought  as  of  perception  and  movement,"  will 
— in  brief — be  "  entirely  physiological."  It  is  not  necessary  to  in- 
quire how  these  two  sentences  can  be  reconciled.  But,  undoubt- 
edly, at  present  the  statement  of  fact  is  far  better  founded  than 
the  anticipation.  It  is  not  easy  to  predict  how  far  psycho-physical 
science  will  be  able  to  push  its  discoveries  in  the  future  ;  or  just 
where  it  will  meet  those  insuperable  barriers  which  surround  all 
fields  of  human  inquiry.  It  is  perfectly  safe,  however,  to  affirm 
of  all  the  phenomena  of  the  so-called  "  higher  faculties  "  of  mind 
what  M.  Ribot  says  of  the  study  of  abstract  concepts — they  still 
"  fall  outside  the  province  of  physiological  psychology."  Certain 
difficulties  are  so  obviously  intrinsic  and  essential  to  the  very  nat- 
ure of  the  facts  with  which  this  science  attempts  to  deal  when  ap- 
proaching these  faculties  that  we  cannot  see  how  they  will  ever  be 
successfully  met. 

§  2.  The  foregoing  conclusions  apply  most  obviously  to  the  for- 
mation of  abstract  concepts,  the  conducting  of  trains  of  reason- 
ing, the  exercise  of  choice,  and  the  activities  of  the  creative  imagi- 
nation in  artistic  production,  scientific  discovery,  or  mechanical 
invention.  They  apply  only  less  obviously  to  the  higher  sesthetic, 
ethical,  and  religious  feelings  ;  although  we  have  already  pointed 
out  certain  facts  and  laws  which  connect  such  feelings  with  a  phys- 
ical basis.  We  are  also  almost  as  much  at  a  loss  how  to  be  "  sci- 
entific "  (strictly  speaking)  in  our  treatment  of  the  phenomena 
which  suggest  some  kind  of  physical  basis  for  the  action  of  will 

'  See  M.  Ribot,  German  Psychology  of  To-day,  p.  306.     New  York,  1886. 
''Ibid.,  p.  15. 


THE   METHOD    OF   IT7QCIRY.  633 

— especiall}'  in  the  direction  of  attention  for  the  apperception  of 
objects  of  sense,  and  for  the  control  of  the  train  of  ideas  or  the 
movement  of  the  bodily  organism.  The  same  thing  is  true  of  the 
phenomena  of  memory,  whether  considered  as  involving  retention 
merely  or  reproduction  as  vs^ell.  All  the  attempts  hitherto  made  to 
explain  or  deduce  consciousness,  either  in  general  or  in  the  par- 
ticular phase  called  self-consciousness,  from  cerebral  functions  and 
activities,  have  been  quibbling  and  wholly  unsatisfactory.  Yet 
there  are  indubitable  proofs  of  the  dependence  of  consciousness  for 
its  existence  and  modes  upon  the  cerebral  centres. 

The  inquiry  after  the  physical  basis  of  the  mental  phenomena 
usually  classed  as  "  higher  "  is,  therefore,  although  peculiarly  in- 
teresting, peculiarly  unjDroductive  of  assured  results.  We  may  sus- 
pect that  there  exist  in  the  nervous  elements  of  the  gray  matter 
of  the  cerebral  hemispheres  inherited  and  acquired  peculiarities  of 
molecular  constitution  and  of  dynamical  combination,  which,  if  we 
could  only  get  at  them,  would  throw  a  flood  of  light  upon  such 
mental  phenomena.  But  after  all,  to  speak  soberly,  we  are  obliged 
to  admit  that  the  very  existence  of  such  peculiarities  is  still  almost 
wholly  a  matter  of  conjecture  ;  while  the  request  for  precise  and 
verifiable  information  as  to  their  nature,  and  as  to  the  laws  which 
connect  them  with  undoubted  facts  of  consciousness,  can  only  be 
met  by  evasion,  confession  of  ignorance,  or  poetizing  and  declama- 
tion under  the  garb  of  science.'  Physiological  Psychology  has  a 
right  to  its  own  hypotheses  ;  it  has,  however,  no  right  to  introduce 
mj^ths  about  the  genesis  and  marriage  and  "erethism"  of  nerve- 
cells,  and  speculation  as  to  nerve-fibres  dynamically  inclined,  into 
the  domain  of  either  physiological  or  psychological  laws. 

§  3.  The  only  safe  method  of  arriving  at  the  few  probable  con- 
clusions attainable  concerning  the  subject  of  this  chapter  is,  accord- 
ingly, the  following  :  The  points  of  starting  and  the  guides  as  to 
the  way  must,  in  nearly  every  case,  be  taken  from  introspective  psy- 
chology. In  studying  the  higher  mental  phenomena,  j)hysiological 
psychology  is  obliged  almost  wholly  to  adopt,  as  the  only  direct 
path  open,  the  ?!0?i-pliysiological  method.  Here,  at  any  rate,  we 
start  from  that  which  appears  to  us  as  terra  firma.  We  know  what 
it  is  to  attend,  to  choose,  to  remember,  and  to  reason — in  short,  to 
be  conscious  in  some  of  the  many  modes  or  phases  of  conscious- 
ness.    Moreover,  whatever  may  be  said  in  disparagement  of  the 

'  It  is  only  by  such  terms  as  "  poetizing"  that  we  can  truthfiilly  characterize 
the  greater  part  of  what  is  said,  for  example,  by  M.  Luys,  in  his  work  on  The 
Brain  and  its  Functions ;  this,  while  admitting  the  skill  and  brilliancy  with 
which  the  author  treats  his  own  interesting  conjectures. 


534  PHYSICAL   BASIS   OF   TOLITIOlSr. 

"  old  psychology,"  it  cannot  fitly  be  denied  that  it  has  most  thor- 
oughly and  subtly  analyzed  the  phenomena  of  judgment,  memory, 
and  choice,  as  these  phenomena  appear  connected  with  each  other 
in  the  flowing  current  of  our  conscious  life.  The  result  of  such 
analysis  has  been  secured  in  the  laws  of  logic,  of  the  association  of 
ideas,  etc.,  and  in  the  various  doctrines  of  the  will  and  its  relations 
to  motive  and  conduct.  In  fact,  all  study  of  these  mental  phenom- 
ena from  the  physiological  point  of  view  is  compelled  to  accept  in 
some  form  the  conclusions  of  a  study  of  the  same  phenomena  from 
the  introspective  point  of  view.  For  example,  the  reproduction  of 
ideas  under  the  so-called  laws  of  association  is  a  general  fact  of 
consciousness  ;  in  the  attempt  to  explain  this  fact  according  to 
j)sycho-physical  causes  we  are  obliged  to  rely  upon  the  results 
reached  by  the  introspective  psj'^chology.  The  application  to  men- 
tal phenomena  of  uncouth  terms  derived  from  the  physical  sciences 
— such  as  "  asfGflutination,"  "  ac'^iomeration,"  "cohesion,"  "organic 
phosphorescence,"  "histological  catalepsy,"  etc. — has  simply  the 
effect  of  repeating  certain  psychical  facts  and  laws  in  a  less  appro- 
priate way,  without  adding  an  item  of  information  regarding  the 
real  nature  of  their  physiological  basis.  Ideas,  or  states  and  prod- 
ucts of  consciousness,  cannot — speaking  litei'ally — cohere,  or  be- 
come agglutinated  or  agglomerated  ;  and  we  need  some  better 
proof  than  mere  declamation  to  show  that  these  states  and  prod- 
ucts depend  upon  any  physical  processes  resembling  agglutina- 
tion, phosphorescence,  or  catalepsy  of  the  nerve-cell.  Physiological 
psychology  is  obliged,  then,  to  accept  certain  conclusions  of  the 
psj'chology  of  self-consciousness  ;  otherwise  it  has  no  motif  ox  guide 
in  its  investigation  of  the  higher  mental  faculties. 

But  while  our  conscious  psychical  experience  of  the  higher  men- 
tal activities  is  so  far  obvious  as  to  make  that  side  of  the  subject 
capable  of  scientific  statement,  our  knowledge  of  the  physiological 
processes  connected  Avith  those  activities  is  in  jDrecisely  the  oppo- 
site condition.  Over  and  over  again  the  confession  has  been  forced 
from  us  that — strictly  speaking — a  scientific  physiology  of  the 
cerebral  hemispheres  does  not  yet  exist.  We  can  only  dimly  con- 
jecture what  takes  place  in  the  nerve-elements  of  the  cortex  of  the 
cerebrum  as  the  physical  basis  of  conscious  sensation  and  percep- 
tion. The  molecular  physics,  or  general  nerve-physiology  of  the 
nerve-muscle  machine — the  simple  peripheral  nerve  with  muscle 
attached — is  in  a  very  unsatisfactory  state.  A  science  for  the  vast 
complex  of  nerve-cells  and  nerve-fibres  which  exists  in  the  gi'ay 
matter  of  the  brain  proper  is  at  present  scarcel}'  a  matter  for  even 
hopeful  anticipation.     Faint  and  doubtful  guesses,  more  or  less 


AUTOMATISM   OF   CENTRAL   OKGANS.  535 

intimately  connected  with  general  principles  of  molecular  physics 
and  physiology  of  the  nervous  system,  are  all  that  can  appear  in 
the  name  of  such  a  science.  But  the  very  business  of  physiological 
psychology  is  to  connect  together  under  general  laws  the  mental 
phenomena,  on  the  one  side,  and  the  ascertained  facts  of  physiol- 
ogy, on  the  other  side.  In  this  case,  we  are  tolerably  equipped 
with  information  as  to  the  former  ;  we  have  little  but  unverifiable 
assumption  to  take  the  place  of  the  latter.  In  attempting  the  in- 
quiry into  the  physical  basis  of  the  higher  faculties  (the  physio- 
logical psychology  of  volition,  memory,  conception,  etc.),  no  other 
course  is  open  but  to  accept  the  facts  of  consciousness,  and  then 
speculate  as  to  how  they  may,  perhaps  in  part,  be  accounted  for  by 
a  conjectural  extension  of  certain  physical  and  physiological  facts 
to  the  cerebral  hemispheres.  This  procedure  certainly  cannot  be 
called  "science ;"  it  is,  however,  the  only  one  open  instead  of  a 
confession  of  complete  ignorance. 

§  4.  The  mental  phenomena  of  the  higher  order,  concerning  whose 
physical  basis  conjecture  is  most  plausibly  supported  by  a  number 
of  related  facts,  may  be  divided  into  two  great  classes.  One  of 
these  covers  the  phenomena  of  Will,  in  the  forms  of  attentive  per- 
ception and  the  effort  determining  the  extent  and  character  of  the 
field  of  consciousness  ;  the  other  covers  the  phenomena  of  Memory, 
whether  considered  as  the  retention  or  the  reproduction  of  ideas. 
Certain  conjectures  as  to  the  physical  basis  of  both  these  kinds  of 
mental  activities  are  in  good  degree  warranted  by  the  principles 
discussed  in  the  foregoing  chapters. 

The  physiological  basis  (so  far  as  such  basis  can  be  said  to  exist) 
for  those  mental  phenomena  which  appear  in  consciousness  as  "acts 
of  will "  is  laid,  in  general,  in  that  power  of  automatism  which  is 
concentrated,  so  to  speak,  in  the  nerve-cells  of  the  central  organs. 
Automatism,  or  the  power  of  originating  motions  which  cannot  be 
explained  as  due  to  external  stimuli,  is  indeed  in  some  sort  a 
property  of  all  living  protoplasm  ;  but  in  that  elaborate  differentia- 
tion of  structure  and  function  which  the  human  body  exhibits,  the 
nei've-cells  of  the  central  organs  have  absorbed  this  power  and  be- 
come distinctively  automatic.  To  them  chiefly  does  it  belong  to 
initiate  within  themselves  the  molecular  changes  which  are  neces- 
sary to  keep  the  body,  both  as  a  whole  and  in  its  several  parts, 
adjusted  to  the  changes  of  its  environment.  It  is  sometimes  said 
that  "  an  amoeba  has  a  will  of  its  own."  Our  only  right  to  speak 
in  this  manner  is  derived  from  the  fact  that  many  of  its  formal 
changes  seem  to  arise  from  within,  and  are  quite  inexplicable  under 
any  known  laws  of  merely  reflex  motion.     If  we  raise  the  inquiry 


533  PHYSICAL   BASIS   OF   VOLITION. 

whether  such  automatic  changes  of  its  molecular  structure  are  ac- 
companied by  anything  which  corresponds  to  what  we  call  conscious 
volition,  it  must  be  admitted  that  we  are  quite  unable  to  answer 
such  an  inquir3^  We  can  easily  imagine  the  amoeba,  however,  to 
have  a  consciousness  of  an  "  act  of  will  "  as  an  accompaniment  of 
each  automatic  change  in  the  arrangement  of  its  molecules.  A 
large  part  of  man's  activit}'  in  the  control  of  his  bodily  organism, 
we  know,  is  unaccompanied  by  any  conscious  volition.  Such  un- 
conscious but  purposeful  activity  belongs  to  the  spinal  cord  and 
to  the  lower  cerebi'al  centres,  which  act  both  reflexly  and  automat- 
ically under  the  laws  of  acquired  skill  and  of  habit.  In  this  way 
many  even  of  our  so-called  voluntary  movements  really  take  place. 
But  some  sudden  emergency — as,  for  example,  the  sight  of  a 
threatening  object,  a  change  in  the  character  of  the  soil  on  which 
the  pedestrian  treads,  the  parting  of  a  rein  in  the  rider's  hand — 
may  call  for  a  succession  of  distinct  and  intense  acts  of  will.  And, 
ordinarily,  mild  and  rather  obscure  volitions  connected  with  the 
movement  of  the  body  intermingle  with  the  succession  of  sensa- 
tions and  ideas  which  compose  the  principal  material  of  con- 
sciousness. 

In  all  such  cases  as  the  foregoing  we  have  reason  to  suppose 
that,  either  through  external  or  internal  stimuli  (either  through 
sensory  impulses  coming  in  along  the  centrijpetal  nerve-tracts  or  as 
started  by  changed  conditions  of  blood-supply),  the  nerve-cells  of 
the  cerebral  hemispheres  are  called  upon  to  exercise  their  peculiar 
functions.  Such  functions  we  may  well  believe  are  always  both 
reflex  and  automatic  ;  that  is  to  say,  the  nerve-commotions  which 
issue  from  the  cells  are  dependent  for  their  intensity  and  charac- 
ter both  upon  the  excitations  coming  to  them  from  without  and 
also  upon  their  own  internal  molecular  structure  and  condition — 
especially  as  respects  the  blood-supply.  Accordingly,  it  must  be 
held  that  volitions,  or  acts  of  will  in  consciousness,  do  not  have 
their  physical  basis  in  any  special  organ  or  area  of  the  brain. 
Tkere  in  no  special  organ  of  loill.  All  the  central  organs  have  pre- 
eminently the  projDerty  of  automatism.  But  since,  in  the  case  of 
man  at  least,  it  is  only  on  occasion  of  a  certain  kind  and  degree  of 
activity  of  the  cerebral  hemispheres  that  what  takes  place  in  the 
nervous  system  has  any  corresponding  expression  in  conscious- 
ness, the  physical  basis  for  acts  of  will  in  general  is  the  automa- 
tism of  these  hemispheres  in  general. 

§  5.  All  act  of  will,  however,  is  always  an  act  of  some  special  kind. 
There  can  be  no  volition  to  motion  in  general,  but  only  a  volition 
defined  and  limited  to  the  movement  of  certain  limbs,  or  of  the 


SIGNIFICAlSrCE   OF   SPECIAL   AEEAS.  537 

trunk  including  the  limbs,  with  a  certain  direction  and  degree  of 
motion.  Thus  also  every  act  of  will  for  the  control  of  the  mental 
train,  or  for  the  apperception  of  an  object  of  sense,  through  con- 
centrated attention,  is  defined  by  some  particular  mental  state  or 
modification  upon  which  it  is  directed.  We  have  seen  good  reason 
to  believe  that  certain  areas  of  the  cerebral  cortex  are  especially 
connected  with  certain  corresponding  sensory-motor  activities 
(comp.  Chap.  II.  throughout).  In  the  same  areas,  then,  the  physical 
basis  is  laid  for  those  acts  of  will  that  are  concerned  with  the 
corresponding  activities.  The  acts  of  will  which  have  to  do  with 
the  movement  of  the  upper  and  lower  limbs,  for  example,  im- 
ply the  special  activity  of  the  cerebral  areas  on  either  side  the 
Fissure  of  Rolando  ;  those  acts  of  will  that  have  to  do  with  the 
movement  of  the  organs  used  in  articulate  speech  are  especially  re- 
lated to  the  areas  lyiug  about  the  lower  part  of  the  Fissure  of  Syl- 
vius— the  posterior  third  of  the  lower  frontal  convolution,  etc.  We 
have  no  sufficient  ground  for  locating  in  one  circumscribed  spot 
the  physical  basis  of  such  acts  of  voluntary  attention  as  concern 
the  different  presentations  of  sense  and  the  images  of  memory  de- 
rived from  them.  The  case  is  not  as  though  the  mind  made  a 
transit,  as  it  were,  from  some  special  seat  of  intelligence  and  will, 
to  contemplate  with  attention  and  pronounce  upon  the  complicated 
sensory  impressions  which  have  arrived  and  been  elaborated  in  the 
particular  sensory  areas ;  or  as  though  it  travelled  from  adjacent 
parts  to  lay  its  grip  upon  the  right  motor  areas  when  sensation  or 
desire  indicated  to  will  that  certain  groups  of  muscles  should  be 
innervated.  Whenever  an  act  of  will  takes  place,  then  at  the  cerebral 
area  lohich  corresponds  to  the  particular  nature  of  the  act  (namely, 
the  will  to  attend  to  this  object  of  sense,  or  to  start  in  motion  that 
limb)  the  particrdar  molecular  changes  arise  in  the  nerve-cells  which 
are  correlated  toith  such  mode  of  consciousness. 

§  6.  As  to  the  relation  in  time  which  is  maintained  between  the 
conscious  act  of  will  and  the  particular  form  of  automatic  cerebral 
excitation  which  we  have  called  its  physical  basis,  it  is  not  possi- 
ble to  pronounce  with  confidence.  But  there  is  no  good  reason 
to  suppose  that  the  conscious  mental  act  is  interpolated  as  an 
independent  element  of  time,  so  to  speak,  among  the  physiological 
processes.  The  flow  of  consciousness  from  obscure  sensation  to 
perception  and  clear  attentive  discernment,  then  to  the  act  of  de- 
cision between  two  or  more  possible  forms  of  appropriate  movement, 
and,  finally,  to  the  issue  of  the  right  fiat  of  will,  all  keep  pace  with 
the  corresponding  physiological  processes  in  the  cerebral  areas. 
As  to  the  exact  nature  of  these  processes,  and  as  to  how  they  fur- 


538  PHYSICAL   BASIS   OF   VOLITION. 

nish  necessary  conditions  to  the  mental  movement,  there  is  no  in- 
formation to  be  imparted. 

§  7.  The  problem  is  complicated  when  our  consciousness  becomes 
one  of  deciding  to  which  of  several  presentations  of  sense  or  im- 
ages of  memory  we  will  to  direct  the  attention.  "  Concerning  the 
physiological  processes,"  saysExner,'  "  from  which  we  abstract  the 
conception  of  attention  we  know  absolutely  nothing."  This  is  true 
even  when  attention  seems  determined  or  forced  upon  us  by  causes 
over  which  the  mind  has  no  control ;  it  is,  of  course,  more  obviously 
true  when  the  mind  is  conscious  of  deliberation  and  choice.  The 
attention  which  directs  to  the  single  object  and  heightens  the  clear- 
ness of  our  perception,  converting  it  into  an  "apperception,"  may 
properly  be  spoken  of  as  an  act  of  loill ;  but  starting  from  the  point 
of  view  of  consciousness,  it  must  be  admitted  that,  in  the  majority 
of  such  activities  of  apjjerception,  there  is  no  consciousness  of  choice 
^— the  will  is  determined  in  one  way.  This  is  equally  true  of  the 
attachment  of  attention  to  certain  particular  images  of  the  mental 
train,  as  that  train  is  conducted  along  under  the  laws  of  association. 
Most  things  which  we  clearly  perceive,  or  feel  with  any  decided 
jDain  or  jDleasure,  or  which  are  vividly  brought  before  the  mind  as 
images  of  memory  and  imagination,  we  cannot  help  attending  to. 
The  sudden  flashing  of  a  light,  the  passing  of  a  bright  object  across 
the  field  of  vision,  the  occurrence  of  a  loud  noise,  or  of  a  fainter 
one  with  a  character  that  interests  us,  the  smells  in  the  atmosphere 
and  the  taste  of  om-  food,  the  sensations  of  the  internal  organs  and 
of  the  skin,  when  sufficiently  intense — all  these  compulsorily  draw 
after  them  the  attention.  They  get  themselves  perceived  by  an  im- 
pulsive and  involuntary  act  of  will.  So,  too,  do  the  revived  images 
of  memory,  in  ordinary  circumstances  where  the  perception  of  ex- 
ternal objects  is  relatively  suppressed,  appear  to  force  themselves 
upon  the  attention. 

In  view  of  the  foregoing  familiar  facts  of  consciousness,  we  may 
conjecture  that  when  the  cerebral  centres  are  not  preoccupied,  as 
it  were,  with  contradictory  forms  and  phases  of  nerve-commotion, 
certain  processes  set  up  within  them,  whether  due  to  external  stim- 
uli or  to  changes  in  the  blood-supply,  are  necessarily  followed  by 
the  phenomena  of  conscious  attention.  Even  when  these  centres 
are  largely  thus  jjreoccupied,  similar  changes  may  be  rapidly  forced 
within  them,  by  the  action  of  some  very  strong  excitation  from  the 
end-organs  of  sense,  or  from  some  connected  cerebral  centre.  Hence 
the  shock  of  surprise  which  sudden  and  vehement  impressions  cre- 
ate. In  all  such  cases  oi forced  attention  the  resulting  tone  of  feel- 
'  In  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  283. 


THE  DIKECTIOlSr   OF  ATTENTIOTT.  539 

mg  in  consciousness  is  different  from  that  which  prevails  when  the 
choice  to  attend  is  being  dehberately  maintained  or  persistently 
revived.  The  motifs  of  much  of  our  activity  of  will  in  attention, 
therefore,  plainly  lie  in  that  state  of  the  cerebral  centres  which  is 
compelled  by  the  intensity  of  the  stimulation  they  receive  (either 
from  external  or  internal  stimuli).'  If  there  were  no  other  phe- 
nomena of  will  than  those  of  forced  attention,  it  would  be  necessary 
to  admit  the  probability  that  all  the  mental  activities  are  purely 
mechanical  and  absolutely  dependent  upon  the  action  of  the  ner- 
vous system  under  the  exciting  influence  of  stimuli. 

§  8.  Certain  phenomena  of  will  in  the  form  of  attention  suggest 
conclusions  of  a  different  order  from  the  foregoing.  Taking  our  point 
of  starting  again  from  consciousness,  we  know  by  a  manifold  expe- 
rience that  the  different  degrees  of  clearness  with  which  we  perceive 
objects  or  apprehend  the  images  of  memory  implies  a  graded  appli- 
cation of  attention.  The  grading  of  this  application  of  attention  is 
by  no  means  always  determined  solely  by  the  intensity  of  the  stim- 
ulus, so  far  as  we  can  measure  such  stimulus.  It  is  a  principle  of 
wide  reach,  that — to  quote  the  words  of  Wundt — "the  degree  of 
apperception  is  not  to  be  measured  according  to  the  strength  of  the 
external  impression,  but  according  to  the  subjective  activity  by 
which  the  consciousness  is  applied  to  a  definite  sense-stimulus." 
The  subjective  activity  which  applies  the  consciousness,  as  it  were, 
to  this  or  that  ^presentation  of  sense  or  image  of  memory,  rather  than 
to  some  other,  is  an  activity  of  will ;  and  the  effect  of  the  activity  is 
seen  both  in  heightening  the  attention  as  directed  to  the  object,  and 
also  in  adapting  the  attention  to  the  particular  object  upon  which  it 
is  directed.  Accompanying  this  twofold  control  of  attention,  and 
indeed  forming  the  veiy  basis  upon  which  it  rests,  when  deliberately 
exercised,  is  the  consciousness  of  "  choice  " — the  activity  of  will  in 
deciding  the  direction  and  amount  of  attention  bestowed  upon  one  ob- 
ject among  several  in  the  f  eld  of  consciousness.  Percepts  and  ideas 
do  not  move  from  the  various  obscurer  parts  of  the  field  of  con- 
sciousness into  the  focal  point  by  virtue  solely  of  a  momentum  be- 
longing to  them  as  such  ;  they  are  placed  and  kept  there  by  an  act 
of  will.  This  must  be  admitted  as  an  indubitable  fact  of  conscious- 
ness, whether  or  not  the  physiological  correlate  or  so-called  explana- 
i  tion  of  this  fact  can  be  discovered  or  even  conjectured. 

Many  indisputably  valid  phenomena,  both  those  accessible  to 
ordinary  observation  and  those  discovered  by  special  experiment, 

'  Comp.  Wxindt,  Physiolog.  Psychologie,  ii. ,  pp.  387  ff.;  and  Stande,  Der  Be- 
griff  d.  Apperception  in  d.  neueren  Psycliologie,  Pliilosoph.  Studieu,  I.,  Heft 
ii.,  p.  194  f. 


540  PHYSICAL   BASIS    OF   VOLITIOX. 

illustrate  the  foregoing  principle.  By  an  act  of  will  attention  may 
be  heightened  and  accommodated  to  the  object,  with  a  marked  in- 
fluence ujDon  apperception  and  the  association  of  ideas.  Upon  this 
point  we  have  to  recall  facts  already  mentioned.  The  effect  of  a 
voluntary  increase  of  attention  upon  the  reaction-time  is  to  diminish 
it,  of  distracted  attention  to  increase  it  or  destroy  its  value  alto- 
gether.' If,  simultaneously,  the  ear  is  stimulated  by  the  periodic 
strokes  of  a  bell,  and  the  retina  by  regularly  recurring  electrical 
sparks,  the  attention  will  naturally  be  directed  to  the  former ;  the 
image  of  the  latter  will  then  be  located  only  very  obscurely  in  the 
flow  of  consciousness,  and  the  time  of  its  occurrence  may  scarcely 
be  noticed  at  all.  We  incline  to  attend  to  the  stronger  of  two  ex- 
citations of  sense  ;  to  yield  to  the  inclination  depresses  the  weaker 
still  further — perhaps  below  the  plane  of  conscious  perception. 
But  within  certain  limits  we  attend  where  ive  ivill.  We  also  incline 
to  attend  to  objects  lying  in  the  point  of  regard  of  the  field  of 
vision,  but  we  can  will  to  attend  to  objects  lying  in  the  outward 
portions  of  this  field.'*  The  voluntary  direction  of  attention  in  this 
case  determines  the  apperception  of  these  objects  to  the  neglect  of 
those  lying  in  the  more  favorable  parts  of  the  field.  We  can  at- 
tend to  the  field  of  vision  of  one  eye,  neglecting  the  other,  as  skil- 
ful microscopists  do.  We  can  see  by  voluntary  attention  the  other- 
wise invisible  double  images.  It  is  claimed  by  some  experimenters 
with  the  "  conflict  of  colors  "  in  binocular  vision,  that,  by  the  direc- 
tion of  .attention,  when  a  green  image  is  formed  on  one  eye  and  a 
red  upon  the  other,  they  can  see  either  at  will,  or  at  will  can  com- 
bine the  two. 

Experiments  with  instantaneous  illumination  by  the  electrical 
spark  also  demonstrate  in  a  marked  way  the  effect  of  attention. 
Objects  which  under  ordinary  circumstances  are  without  great  effort 
seen,  either  as  stereoscopic  or  as  double  images,  can  also  be  seen 
in  both  ways  by  the  electric  spark,  according  to  the  direction  of 
attention.  The  first  impression  is  ordinarily  stereoscopic  ;  but  if  a 
pause  of  10  sec.  be  allowed  for  the  after-images  to  die  away,  the 
experimenter  can  at  will  see  the  double  images,  although  the  point 
of  fixation  and  the  influence  of  the  light  remain  absolutely  the 
same.^      The  effect  of  attention  in  analyzing   composite  musical 

'  See  the  table  of  Obersteiner,  Brain,  I.,  p.  439,  to  show  the  fluctuations  of 
the  reaction-time  of  a  person  reacting  while  an  organ  was  playing  in  the  same 
room.  The  normal  reaction  time  of  the  person  being  0.100  sec,  it  rose  to 
0.148,  and  even  0.215,  while  the  instrument  was  heard,  and  fell  to  0.095  and 
0.087  during  pauses  in  the  playing. 

-'  See  Helmholtz,  Physiolog.  Optik,  p.  740  f.  '■^  Ibid.,  p.  741. 


EFFECT   OF   ATTENTIOIST   OJST   MEMOEY.  541 

clangs  into  their  elements  is  equally  marked.'  In  addition  to  a 
previous  acquaintance  with  the  character  of  such  over-tones  as  are 
to  be  expected  and  analyzed  out  of  the  clang,  the  analysis  can  take 
place  in  no  case  w^ithout  a  "  certain  undisturbed  concentration  of 
the  attention."  That  changes  in  the  clearness  of  perceptions  take 
place  in  dependence  on  the  changes  in  the  degree  of  attention  is  a 
matter  of  the  most  ordinary  experience.  On  waking  gradually 
from  sleep  our  surroundings  become  less  and  less  obscure  to  the 
senses  of  eye,  ear,  and  skin,  as  the  grade  of  voluntary  attention  in 
apperception  progressively  rises.  On  casting  the  glance  casually 
upon  a  landscape  seen  through  a  window,  its  objects  are,  at  first, 
scarcely  perceived  at  all ;  by  gradual  increase  in  the  intensity  of 
attention  (changing  the  casual  glance  into  a  steady  look)  these 
objects  become  apperceived  more  and  more  clearly.  The  voluntary 
concentration  of  attention  (comp.  p.  446  f.)  often  dissolves  an  error 
of  sense  or  changes  the  entire  appearance  of  the  visual  object  On 
the  other  hand,  a  great  strain  of  attention  may  lead  one  to  anticipate 
an  expected  impression  of  sense,  and  perceive  its  occurrence  before 
it  has  actually  taken  place.  It  may  also  cause  other  illusions,  as 
when,  on  expecting  eagerly  the  stroke  of  the  clock,  some  weaker 
sound  may  be  mistaken  for  it." 

§  9.  Voluntary  attention  directed  toward  the  images  of  memory 
has  also  a  marked  effect  upon  their  character  and  duration  in  con- 
sciousness. In  certain  cases  it  may  impart  to  them  the  vividness 
of  presentations  of  sense,  although  the  power  to  bring  this  about 
differs  greatly  for  the  different  senses  and  in  different  individuals. 
By  an  effoi't  of  will  the  player  of  a  musical  instrument  can  cause 
himself  to  feel  again  the  revived  images  of  the  muscular  and  tactual 
sensations  which  accompanied  a  particular  exercise  of  his  skill. 
The  hearer  of  some  impressive  musical  air  may  voluntaril}'  set  it 
running,  with  its  variation  of  tone  and  rhythm,  through  his  mind's 
ear,  as  it  were.  Not  to  speak  of  hallucinations  and  visions,  most 
men  see  sights  in  dreams,  and  even  in  reverie,  that  closely  approach 
the  intensity  of  the  presentations  of  sense  in  the  waking  state  and 
in  broad  daylight.  Artists  in  forms  of  art  involving  a  special  sus- 
ceptibility and  activity  of  some  one  or  more  of  the  senses,  are,  of 
course,  gifted  with  a  specialized  creative  energy  of  imagination. 
Particular  images  of  memory  may  be  seized  upon  at  will,  as  it  were, 
and  the  attention  so  concentrated  upon  them  as  to  impart  to  them 
much  of  the  strength  which  their  originals  enjoyed. 

Moreover,  the  effect  of  attention  upon  certain  images  of  memory 

'  Helmholtz,  Die  Lehre  von  den  Tonempfindungen.  etc.,  p.  84  f. 
*  See  Fecliuer,  Eiemente  d.  Psycho-pliysik,  ii.,  p.  491  f. 


542  PHYSICAL   BASIS    OF   VOLITION". 

is  such  as  apparently  to  localize  them  anew  in  the  organs  by  which 
these  originals  were  formed.  To  try  to  revive  a  melody  as  distinctly 
as  possible  produces  a  sense  of  strain  (a  feeling  of  being  innervated) 
in  the  region  of  the  ear.  We  recall  sounds,  especially  if  we  recall 
them  vividly,  with  the  organs  of  hearing.  The  prolonged  effort  to 
recall  or  image  colors  or  visual  forms  tires  the  visual  organs  ;  the 
impression  is  as  though  the  recollection  or  imagination  were  accom- 
plished in  and  through  these  organs.  The  violin-player  remembers 
and  goes  over  the  solo  he  is  to  play,  not  only  in  his  ear,  but  in  his 
arms  and  fingers.  Upon  such  power  of  reproduction  the  power  of 
new  jDroduction  depends.  Indeed,  we  may  say  that  "  the  activity 
of  voluntary  sensuous  attention  largely  consists  in  a  voluntary  re- 
production of  earlier  conditions  of  sensations."  '  It  has  even  been 
claimed  that  vivid  representative  images  of  color-sensations  may  be 
followed  by  the  corresponding  negative  after-images.^ 

§  10.  Concerning  the  physiological  basis  of  the  phenomena  of 
voluntary  attention,  little  is  known.  Apparently,  j^art  of  the  effect 
must  be  due  to  the  changed  condition  which  is  brought  about  in 
the  end-organs  of  sense  when  especially  innervated  and  so  j^repared 
for  receiving  the  stimulation  approjDriate  to  them.  To  this  fact  is 
due  the  peculiar  feeling  of  strain  in  the  oi'gan  of  attentive  apper- 
ception, or  of  vivid  reproduction  of  the  image  of  memory.  But 
the  chief  effect  of  attention  is  realized  in  the  altered  condition  of 
the  cerebral  centres.  It  is  only  obvious,  according  to  Exner,'  that 
we  have  to  do  with  changes  in  the  central. mechanism  set  up  by  act 
of  will,  and  that  these  changes  vary  quantitatively  and  concern  the 
circles  of  our  psychical  activity.  Moreover,  the  point  of  attach- 
ment, as  it  were,  for  the  attention  is  found  only  after  the  impres- 
sion of  sense  has  been  elaborated  to  a  certain  degree.  We  cannot 
voluntarily  attend  without  perceiving,  at  least  obscurely,  that  to 
which  (presentation  of  sense  or  image  of  memory)  attention  is  to 
be  directed.  Still  further,  fluctuations  of  the  cerebral  activity 
are  constantly  occurring  ;  for,  as  every  one  knows  who  has  expe- 
rimented with  himself  (for  example  in  determining  reaction-time), 
it  is  impossible  to  keep  attention  on  a  perfectly  steady  stretch  with 
respect  to  its  object.  Waves  of  consciousness  in  connection  with 
these  fluctuations  of  attention  rise  and  fall.''  In  the  most  suc- 
cessful reactions  the  attention  is  effectual  in  producing  and  main- 

'  Comp.  G.  E.  Miiller,  Zur  Theorie  d.  siiinliclien  Aufmerksamkeit,  Leipzig, 
p.  89. 

^  Wundt,  Vorlesungen  iiber  Mensch  u.  Thier,  I.,  p.  387. 

'  In  Hermann'.s  Handb.  d.  Physiol.,  II.,  ii.,  p.  283. 

*  Comp.  Fecliner,  Elemeiite  d.  Psycho-pliysik,  ii  ,  p.  452  f. 


INFLUEISrCE   OF   THE   FRONTAL   EEGIONS.  543 

taining  a  state  of  strained  expectation,  in  which  the  occurrence  of 
the  expected  stimulation  sets  the  motor  mechanism  off  without,  and 
even  in  spite  of,  a  separate  act  of  wiU.  In  such  cases  the  cei'ebral 
centres  have  apparently  been  thrown  into  an  exalted  and  explosive 
state  of  irritability.  We  all  know  that  very  little  suffices  to  set  the 
muscles  agoing  when  the  mind  is  on  the  stretch.  It  is  not  unlikely 
that  the  effect  of  attention  is  felt  in  depressing  certain  cerebral 
areas  not  intimately  connected  with  the  production  of  the  particular 
image  of  memory  or  presentation  of  sense,  as  well  as  in  heightening 
the  activity  of  others  that  are  thus  connected.'  The  phenomena,  at 
any  rate,  imply  an  increased  difference  of  excitability  and  conductivity 
for  their  specific  forms  of  nerve-commotion  in  the  different  cerebral 
areas.  Under  the  influence  of  attention  the  cerebrum  has  become 
more  susceptible  for  certain  impressions,  less  so  for  certain  others.^ 
Stored  energy  of  the  nerve-cells  is  being  rapidly  called  forth.  Con- 
centrated voluntary  attention  implies  a  large  amount  of  ivork  being 
done  in  the  cerebral  hemispheres.  We  recognize  this  fact  in  the  ac- 
companying feelings  of  strain  and  in  the  subsequent  feelings  of 
brain -exhaustion.  The  subject  of  experiment  to  determine  the 
reaction-time  under  concentrated  attention  often,  though  sitting 
quiet,  sweats  profusely. 

§11.  What  happens  when  two  different  excitations,  arising  either 
from  conflicting  presentations  of  sense,  or  conflicting  ideas,  meet  in 
any  single  region  of  the  brain  ?  We  can  only  answer  this  question 
with  vague  conjecture.  The  phenomena  of  the  conflict  of  colors  in 
binocular  vision  seem  to  imply  that  either  the  more  intense  of  the 
two  may  prevail  over  the  other,  or  the  two  may  both  persist  and 
interpenetrate  as  it  were.  In  certain  cases  voluntary  attention 
may  determine  which  event  shall  ensue.  The  sugar  sweetens  the 
acid  of  the  lemonade,  not  in  the  vessel  which  contains  it  or  on  the 
tongue  which  tastes  it,  but  in  the  brain.  According  to  the  con- 
jecture of  Wundt,^  the  frontal  regions  of  the  cerebrum  are  the 
"bearers  (Trdger)  of  the  physiological  processes  which  accompany 
the  apperception  of  the  presentations  of  sense."  In  order,  then, 
that  the  process  set  up  in  any  cerebral  region  by  an  excitation  of 
the  organs  of  sense  connected  with  it  may  result  in  clear  discern- 
ment of  an  object,  certain  physiological  processes  must  be  con- 
ducted from  the  frontal  regions  to  that  region.  Wundt's  con- 
jecture is  plausible,  at  least  it  gives  the  frontal  region  something 
to  do,  and  answers  in  part  the  inquiry  why  so  much  of  the  cere- 

'  See  G.  E.  Miiller,  Zur  Theorie  d.  sinnliclieu  Aufmerksamkeit,  p.  52  f. 
-  See  Exner,  in  Pfliiger's  Arcliiv,  xi.,  p.  428. 
^  Physiolog.  Psycliologie,  i. ,  p.  218. 


644  PHYSICAL   BASIS    OF   VOLITION. 

bral  substance  should  seem  merely  negative  as  respects  the  phe- 
nomena of  sensation  and  motion. 

§  12.  Nothing  thus  far  said,  and  nothing  of  scientific  value  which 
physiological  psychology  has  to  offer,  throws  any  clear  light  on  the 
problem  of  the  "freedom  of  the  will."  When  M.  Luys,'"  for  exam- 
ple, maintains  that  to  imagine  "  we  think  of  an  object  by  a  spon- 
taneous effort  of  mind  is  an  illusion,"  and  that,  in  fact,  the  object  is 
only  forced  on  us  by  the  cunning  conjurer,  the  brain,  "because  the 
cell-territory  where  that  object  resides  has  been  j)reviously  set  vi- 
brating in  the  brain,"  he  is  controverting  a  plain  and  universal 
dictum  of  consciousness  by  his  private  and  unverifiable  hypothesis 
on  a  question  of  cerebral  physiology  where  exj^erts  and  novices  are 
alike  ignorant.  Physiology  neither  disproves  nor  verifies  the  post- 
ulate of  free  will  ;  accordingly,  this  postulate  must  be  raised  and 
discussed  upon  other  grounds.  Metaphysics  and  ethics  cannot 
properly  dictate  their  facts  and  conclusions  to  the  science  of  physi- 
ological psychology  ;  but,  in  turn,  this  science  cannot  properly 
dictate  to  metaphysics  and  ethics  the  conclusions  which  they  shall 
draw  from  facts  of  consciousness,  by  giving  out  its  myths  and  fa- 
bles in  the  garb  of  well-ascertained  history  of  the  cerebral  pro- 
cesses. 

§  13.  Consciousness,  or  the  having  any  form  of  sentient  life,  in 
distinction  fi'om  being  in  a  condition  of  dreamless  sleep  or  swoon- 
ing, and  Self-cousciousness,  or  the  recognition  of  the  states  of  con- 
sciousness as  states  of  the  ego  or  subject  of  them  all,  are  inti- 
mately connected  with  the  johenomena  of  will.  By  the  amount 
and  speed  of  the  energy  expended  in  attention  we  measure  in  large 
degree  the  extent  and  intensity  of  consciousness.  The  stir  of  feel- 
ing through  the  presentation  of  some  object  of  sense,  or  through 
some  idea,  causes  us,  either  voluntarily  or  involuntarily,  to  rouse 
ourselves  to  what  is  then  recognized  as  a  wider  and  higher  energy 
of  consciousness.  But  inasmuch  as  consciousness  is  the  condition 
of  all  internal  experience  whatsoever,  we  cannot  deduce  or  explain 
the  essential  nature  of  consciousness  from  other  forms  of  such  ex- 
perience.^    For  the  same  reason  we  cannot  define  consciousness. 

Concerning  the  physical  basis  of  consciousness  little  can  be  added 
to  Avhat  has  already  been  said  concerning  the  physical  basis  of 
the  various  foi-ms  of  consciousness.  Consciousness  is  never  con- 
sciousness in  general — never  an  activity  or  state  that  ma}-  be  sep- 
arated from  the  individual  states  and  processes  of  consciousness. 
In  the  case  of  man,  the  cerebrum  is  apparently  the  sole,  as  it  cer- 

'  The  Brain  and  its  Functions,  p.  254. 

'  Comp.  Wundt,  Physiolog.  Psytfliologie,  ii. ,  p.  195  f. 


CONDITIONS    OF   CONSCIOUSNESS.  C45 

tainly  is  the  chief,  organ  of  consciousness  (comp.  pp.  249  ff.).  By 
calling  the  cerebrum  the  "  organ  "  of  consciousness,  however,  little 
more  is  meant  than  that  the  constitution  and  processes  of  the  ner- 
vous matter  of  this  organ  are  related  in  the  most  immediate  and 
special  way  to  all  mental  phenomena,  and  that  what  takes  place  in 
material  elements  outside  of  the  cerebrum  (including  the  elements 
of  the  other  portions  of  the  nervous  system)  has  an  effect  iipon  con- 
sciousness only  in  case  it  gets  itself  represented,  as  it  were,  in  the 
corresponding  cerebral  processes.  As  to  a  special  organ  of  con- 
sciousness in  the  brain — that  is,  a  cerebi'al  area  where  the  mind 
comes  to  consciousness — it  is  not  proper  to  speak. 

Accordingl}^,  the  physical  basis  of  the  diiferent  forms  of  con- 
sciousness is  laid  in  those  cerebral  areas  which  have  been  found 
to  be — or,  though  still  undiscovered,  actually  are — especially  con- 
nected with  these  forms.  But  if  the  question  is  further  pressed  as 
to  the  physical  basis  for  the  activities  of  self-consciousness,  no  answer 
can  be  given  or  even  suggested.  From  its  very  nature  that  mar- 
vellous verifying  actus  of  mind  in  which  it  i-ecognizes  itself  as  the 
subject  of  its  own  states,  and  also  recognizes  the  states  as  its  own, 
can  have  no  analogous  or  corresponding  material  substratum.  It 
is  impossible  to  specify  any  physiological  process  representing  this 
unifying  actus  ;  it  is  even  impossible  to  imagine  how  the  descrip- 
tion of  any  such  process  (in  case  we  knew  what  to  attempt  to  de- 
scribe) could  be  brought  into  intelligible  relation  with  this  unique 
mental  power. 

In  general,  concerning  the  physical  conditions  of  consciousness,  it 
is  known  that  they  are  dependent  upon  the  character  and  amount 
of  the  blood-supply.  To  stop  this  supply  is  to  put  an  end  for  the 
time  to  consciousness ;  to  impede  or  corrupt  it  is  to  depress  and  to 
disturb  consciousness  ;  to  alter  its  character  is  to  affect,  more  or 
less  promptly  and  profoundly,  the  character  of  consciousness.  The 
character  of  the  circulation  in  the  cerebrum  largely  determines  the 
nature  of  the  phenomena  of  consciousness.  Quickened  circulation 
here  accelerates  or  agitates  the  circuit  and  time-rate  of  conscious- 
ness ;  slower  circulation  diminishes  and  inhibits  them.  It  has 
been  alleged  by  Mosso  that  certain  changes  in  the  relative  circula- 
tion of  the  human  body  occur  when  the  attention  is  occuj^ied  in- 
tensely either  with  external  imj)ressions  or  with  psjThical  work. 
Such  observations  are  not  as  yet  extended  and  accordant  enough 
to  command  unhesitating  assent  to  the  details  of  their  results. 

§  14.  The  other  group  of  so-called  higher  mental  phenomena 
which  admits  of  the  most  of  probable  conjecture  regarding  the  nat- 
ure of  its  physical  basis  comprises  Memory,  as  retentive  and  re- 
35 


546  PHYSICAL   BASIS   OF   MEMORY. 

productive,  and  the  laws  of  the  Association  of  Ideas.  The  experience 
of  consciousness  is  one  of  a  constantly  changing  succession  of  states. 
The  rise  and  fall  in  voluntary  or  involuntary  attention,  and  the 
change  of  its  direction,  are  accompanied  by  a  continual  alteration 
of  the  phases  and  of  the  circuit  of  consciousness.  Of  these  shifting 
mental  states  certain  ones  bear  the  peculiar  mark  of  a  claim  to  rep- 
resent previous  states  of  consciousness,  in  some  regard  and  to  some 
extent  similar  to  themselves.  The  image  of  memory  is  itself  a  prod- 
uct, a  phase,  of  present  consciousness  ;  it  is  not  itself  of  the  past, 
and  yet  it  claims,  by  virtue  of  its  essential  character,  to  stand  for 
the  past.  This  claim  can,  of  course,  in  no  instance  be  verified  by 
carrying  the  consciousness  back  to  that  past ;  we  are  never  able  by 
attentive  apperception  to  compare  the  image  of  memory  with  its 
alleged  original  and  thus  make  sure  of  the  validity  of  the  claim. 
Experience  also  teaches  us  that  the  mental  images  do  not  come 
and  go  wholly  at  random  and  irrespective  of  the  characteristic  con- 
tent of  such  as  are  most  closely  connected  in  time.  That  these 
images  are  associated  in  time  is  a  part  of  the  fundamental  fact  of 
memory ;  mental  states  are  not  states  of  memory  without  some 
more  or  less  definite  localization  of  the  ideas  thus  presented  to  the 
mind  with  reference  to  its  past. 

Further  examination  of  the  particular  character  of  the  ideas 
which  most  frequently  occur  simultaneously,  or  in  closest  succes- 
sion, has  given  rise  to  the  assumption  that  the  images  of  memory 
are  associated  in  a  regular  way.  Hence  those  general  facts  of  psy- 
chology called  the  "laws  of  the  association  of  ideas."  From  the 
phenomena  of  memory  and  reminiscence,  as  experienced  in  the 
consciousness  of  the  individual,  arises  the  belief  that  the  objects  of 
past  experience  are  retained  in  the  mind,  and  that  they  suggest  each 
other  (at  least  ordinarily)  in  some  orderly  way.  But  properly 
speaking,  the  "  retention  "  of  states  of  consciousness,  whether  of 
ideas  or  of  presentations  of  sense,  is  not  a  faculty  or  power  of 
mind.  To  ask,  Where  is  the  idea  I  once  had,  or  the  object  I  once 
saw,  between  the  time  of  the  original  experience  and  the  time  of 
recall,  is  to  ask  a  question  that  can  have  only  one  answer.  Such 
idea  or  presentation  of  sense  is  nowhere,  for  it  does  not  exist  in 
any  sense  of  the  word  whatever.  Both  presentation  of  sense  and 
image  of  memory  are  transitory  phases  of  consciousness,  each  per- 
ishes with  that  phase  of  consciousness  in  which,  and  as  which,  it 
has  its  existence.  It  is  the  power  of  recall  solely  which  induces  us 
to  speak  as  though  the  mental  object  were  retained  or  kept  in  the 
Mind.  It  is  only  m  the  facts  and  laws  of  conscious  reproduction  that 
any  trace  of  the  activity  of  mind,  as  memory,  is  to  he  found.     Much 


PRIMAEY   IMAGE   OF   MEMOKT.  547 

"  cerebration  "  may  be  unconscious  ;  there  may  be  considerable 
periods  of  complete  unconsciousness  in  tlie  daily  life  of  every  indi- 
vidual, as  there  certainly  are  such  periods  occasionally^  in  the  lives 
of  some  individuals.  But  of  unconscious  retention  or  reproduction 
of  ideas  as  an  activity  of  mind,  there  is  none. 

§  15.  Both  ordinary  observation  and  experiment  in  reaction-time 
indicate  that  the  speed  with  which  the  images  of  memory  vanish 
depends  upon  a  variety  of  circumstances — such  as  individual  pe- 
culiarities, intensity  and  frequency  of  the  repetition  of  the  original 
impression,  condition  of  the  cerebral  centres  and  of  the  conscious- 
ness at  the  time  of  this  impression,  etc.  The  thousands  of  faint 
impressions  which  enter  into  every-day  life  seem  quickly  to  A^anish, 
without  leaving  a  trace  behind  in  either  body  or  mind.  But  that 
these  impressions  do  linger  for  a  time  in  memory,  as  we  say,  or 
are  reproducible  in  consciousness  under  the  form  of  images  of 
memory,  there  can  be  no  doubt.  For  example,  if,  while  one  per- 
son is  intently  counting  the  lines  of  a  page  or  adding  a  column  of 
figures,  another  near  by  makes  some  slight  motion,  the  image  of 
the  motion  in  the  mind  of  the  former  may  be  recalled  within  a  few 
seconds  of  the  occurrence  ;  a  little  later,  however,  such  an  image 
may  have  so  completely  vanished  that  the  observer  will  declare  the 
motion  was  not  noticed  at  all.'  The  vividness  of  fresh  images  of 
memory  may  be  so  great  as  even  to  make  it  difficult  to  distinguish 
them  from  true  presentations  of  sense.  But  even  in  the  case  of 
impressions  made  clear  and  strong  by  the  strenuous  concentration 
of  attention,  the  vividness  of  the  image  of  memory  diminishes  at 
first  very  quickly.  Even  in  such  a  case  the  so-called  "  primary  '' 
image  of  memory  may  not  last  beyond  a  few  minutes  ;  while  in 
cases  where  there  is  little  attentive  apperception  this  image  van- 
ishes in  a  few  seconds.^  Let  a  hne  of  given  length  be  regarded  for 
a  brief  time,  then  removed,  and  after  a  varying  interval  the  eflbrt 
made  to  recall  its  image  so  as  to  compare  it  accurately  with  another 
line  of  nearly  the  same  length.  It  will  be  found  that  the  clearness 
of  the  image  of  memory,  which  quickly  falls  off  at  first^  falls  off 
afterward  more  slowly,  and  finally  approximates  more  nearly  to  a 
stationary  condition.  Lotze  ^  has  insisted  upon  the  caution  that 
we  should  not  confuse  the  clearness  of  ideas  with  their  intensity  ; 
the  idea  of  the  most  intense  brightness  is  not  intensely  bright.  Yet 
we  cannot  agree  with  Lotze  in  the  opinion  that  the  ideating  activity, 
when  applied  to  the  recall  of  sensations,  does  not  diflfer  in  intensity 

'  See  Exner,  in  Hermann's  Handb.  d.  Physiol.,  II.,  ii.,  p.  281  f. 
'^  Comp  Fecliner,  Elemente  d.  Psycho  physik,  ii.,  p.  491. 
^  Outlines  of  Psychology,  p.  28  f. 


548  PHYSICAL   BASIS    OF   MEMOllY. 

as  well  as  in  clearness.  Besides  the  difference  in  the  clearness  with 
which  two  persons,  for  example,  remember  a  mosaic  of  colors,  as  re- 
spects all  the  details  of  what  particular  colors  were  arranged  in  what 
particular  order,  there  is  also  a  difference  in  the  strength  which  the 
various  revived  images  of  the  colors  have  in  the  two  consciousnesses. 

§  16.  That  the  mental  phenomena  which  lead  us  to  speak  of  the 
retentive  power  of  memory  have  a  physical  basis  there  can  be  no 
doubt.  This  conclusion  is  warranted  by  the  nature  of  the  phenom- 
ena themselves,  by  the  impossibility  (already  alluded  to)  of  con- 
ceiving of  a  permanent  modification  of  unconscious  mind,  and  by 
all  that  we  know  of  the  principles  of  biology  in  general  and  of  hu- 
man physiology  in  pai'ticular.  Every  sensory  impulse,  and  every 
combination  of  such  impulses,  must  produce  changes  both  in  the 
end-organs  and  in  the  central  organs  ;  and  although  these  changes 
vanish,  so  far  as  their  effect  in  the  corresponding  phenomena  of 
conscious  mind  is  concerned,  they  nevertheless  cannot  fail  to  leave 
the  organs  in  different  condition  from  that  in  winch  they  found 
them.  As  a  matter  of  course,  the  effect  of  stimulus  upon  every 
end-organ  of  sense  consists  in  the  production  of  molecular  changes, 
which,  on  account  of  the  principle  of  inertia  as  applied  to  such  or- 
gan, continue  for  a  time  after  the  stimulus  has  been  removed.  Of 
this  fact  the  existence  of  the  after-images  on  the  retina  is  the  most 
notable  example.  The  successive  stages  passed  through  by  the  af- 
ter-images, both  jDositive  and  subsequently  negative,  are  themselves 
indicative  of  a  sei-ies  of  molecular  changes  set  up  by  the  action  of 
the  stimulus.  But  the  effects  of  stimulus  must  also  be  felt  in  the 
production  of  molecular  changes  in  the  central  organs,  in  the  nerve- 
elements  (especially  the  nerve-cells)  of  the  cei'ebral  hemispheres, 
if  the  sensory  impulses  are  to  result  in  conscious  sensation  and  per- 
ceiDtion.  Experience  would  then  lead  us  to  infer,  farther,  that  each 
combination  of  sensations  produces  changes  in  the  cerebral  hemi- 
spheres which  outlast  the  action  of  the  stimulus  upon  the  end-organ 
of  sense.  A  study  of  consciousness,  simply  as  consisting  of  chang- 
ing sensations  and  perceptions,  might  appear  to  indicate  that  the 
after-forms  of  molecular  changes  themselves  die  out  and  leave  the 
end-organs  and  cerebral  centres  in  precisely  the  same  condition 
as  before.  But  the  formation  of  habits  of  perception  and  motion, 
the  phenomena  of  conscious  mental  reproduction,  and  the  general 
principles  of  molecular  science  as  applied  to  the  nervous  mechan- 
ism, suggest  and  enforce  another  view. 

Certain  experiences  in  the  use  of  the  senses  show  that  molecular 
activities  induced  in  the  end-organs  by  stimulation  may,  under  cer- 
tain circumstances,  persist  much  longer  than  we  are  at  first  inclined 


rOEMIiSTG   OF   MOLECULAR  TENDEISTCIES.  549 

to  suppose.  For  example,  a  study  of  the  after-images  left  by 
strong  impressions  on  the  retina  shows  that  traces  of  them  recur 
again  and  again,  even  several  minutes  after  the  eyes  have  been 
closed.  Prolonged  work  with  the  microscope  will  cause  the  images 
seen  in  its  focus  to  "  live  in  the  fundus  of  the  eye  "  so  that,  after 
several  hours,  shutting  the  eyes  will  cause  these  images  to  reappear 
with  great  distinctness.  Of  a  similar  kind  is  our  experience  with 
sounds — the  rattle  of  the  railroad-car  after  a  long  journey,  the  im- 
pressive cries  or  words  to  which  we  have  listened,  the  successive 
notes  and  chords  of  the  musical  composition  heard  at  a  concert, 
seem  to  be  repeated  in  the  ear  for  hours  after  the  primary  sensa- 
tions have  subsided.  According  to  Dr.  Moos,'  after  long  musical 
seances  the  sounds  persisted  for  fifteen  days  in  one  patient ;  and  a 
professor  of  music  was  accustomed  to  hear  over  again  the  notes 
sounded,  for  several  hours  after  each  lesson.  After  startling  and 
impressive  experiences  with  different  kinds  of  sense-percepts — 
sounds,  sights,  etc. — it  is  not  an  uncommon  thing  for  the  same 
bodily  affections  to  recur  with  such  vividness  as  to  make  it  almost 
impossible  at  the  instant  to  distinguish  them  from  fresh  experi- 
ences of  the  same  kind. 

Moreover,  all  those  inherited  and  acquired  unconscious  habits  of 
motion,  with  which  the  study  of  the  nervous  mechanism  has  already 
made  us  familiar,  imply  that  the  effects  of  repeated  stimulations 
persist  in  the  molecular  constitution  and  tendencies  to  molecular 
change  of  the  nervous  substance  of  the  central  organs.  The  puppy 
which  has  inherited  a  brain  and  spinal  cord  embodying  the  habits 
of  his  race,  and  the  trained  gymnast  or  skilled  player  on  a  musical 
instrument,  alike  illustrate  this  principle  of  stored  and  organic  ex- 
perience as  pertaining  to  the  elements  of  the  nervous  system.  The 
general  principle  of  molecular  science,  which  finds  numerous  ex- 
amples both  in  inorganic  chemistry  and  in  biology,  compels  a 
similar  conclusion  as  to  the  physical  basis  of  memory.  The  estab- 
lished practice  of  jDhotography  depends  ujDon  the  fact  that  a  plate 
of  dry  collodion,  after  being  briefly  exposed  to  the  sun's  rays,  re- 
tains for  weeks,  in  the  darkness,  the  effects  of  the  indescribably  deli- 
cate changes  which  have  been  brought  about  in  it.  The  "  latent 
image  "  contained  in  it  may  be  revived  by  proper  treatment.  The 
phenomena  of  phosphorescence,  also,  show  that  the  impressions  of 
the  luminous  undulations  persist  in  certain  bodies  for  a  consider- 
able time  after  these  undulations  themselves  have  ceased  acting. 
Niepce  de  Saint- Victor  "^  has  shown  that  such  undulations  may  be 

'  So  Lays,  The  Brain  and  its  Functions,  p.  136. 

-  Comptes-reudus  de  1  Academic  des  Sciences,  xlv. ,  p.  811  ;  and  xlvi.,  p.  448. 


550  PHYSICAL   BASIS   OF   MEMORY. 

"  to  some  extent  garnered  up  in  a  sheet  of  paper,"  ready  to  be  re- 
vealed at  the  call  of  special  reagents.  Inasmuch  as  the  nervous 
system  consists  of  an  inconceivably  complicated  and  delicate  molec- 
ular mechanism,  every  element  of  which  may  be  regarded  as  a 
highly  complex  molecular  structure,  it  may  well  be  expected  to  ac- 
complish much  more  wonderful  results  than  the  plate  of  dry  col- 
lodion or  sheet  of  paper,  in  the  way  of  storing  up  for  future  de- 
maud  the  results  of  the  impressions  made  upon  it.  We  may  even 
go  so  far  as  to  say  that  the  retentive  power  of  this  molecular  mech- 
anism is  perfect ;  that  it  never  loses  entirely  the  effect  of  any  im- 
pression  once  made  upon  it. 

§  17.  In  view  of  such  considerations  as  the  foregoing  it  has  been 
proposed  by  some  writers  to  regard  memory  simj^ly  as  one  phase 
of  the  general  biological  fact,  as  a  particular  form  of  synthesis  "  of 
one  of  the  primordial  properties  of  the  nervous  elements."  Con- 
scious memory- is  then  considered  as  "a  phosphorescence  of  the 
nervous  elements  "  pZws  consciousness  ;  and  this  power  of  these 
elements  itself  is  to  be  called  a  power  of  "  unconscious  reminis- 
cences "  (M.  Luys)  or  an  "  oi-ganic  memory  "  (Hering  and  M.  Ribot). 
But,  while  admitting  the  general  fact  of  molecular  science,  and  the 
application  of  it  to  the  phenomena  of  habit  in  the  nervous  mechan- 
ism as  contributing  something  to  the  description  of  the  physical 
basis  of  conscious  memory,  it  is  wise  to  refuse  to  use  such  terms  as 
the  foregoing.  For  tJiese  terms  are  not  needed  to  state  the  facts  ; 
of  themselves  they  lend  nothing  to  the  desired  explanation,  and 
they  are  liable  to  lead  to  serious  confusion.  "  Organic"  memory, 
or  the  habitual  mode  of  the  behavior  of  the  nervous  system,  to- 
gether with  that  tendency  to  reproduce  the  mode  which  belongs 
to  all  habits,  when  minus  consciousness,  is  not  memory  at  all ;  it 
bears,  indeed,  no  resemblance  to  memory.  "  Unconscious  "  reminis- 
cence, regarded  as  a  function  of  material  elements,  is  not  reminis- 
cence at  all. 

Moreover,  when  we  inquire  as  to  precisely  what  constitutes  this 
wonderful  jjower  of  conserving  the  results  of  molecular  changes 
induced  by  the  action  of  stinmli,  which  the  nervous  system  pos- 
sesses, we  find  it  impossible  to  give  a  wholly  satisfactory  answer. 
The  most  plausible  answer  consists  in  inferences  touching  the 
highly  probable  apj^lication  of  certain  biological  laws  to  the  special 
case  of  the  nervous  system,  regarded  as  furnishing  a  physical  basis 
for  the  phenomena  of  memory.  The  general  fact  from  which  these 
inferences  take  their  point  of  starting  is  undoubted  ;  the  entire 
nervous  mechanism  must  be  regarded  as  a  vast  system  of  interrelated 
elements  (nerve-iibres  and  nerve-cells),  each  of  which  must  also  be 


EFFECT    OF    ALTEKEP    ISTUTEITION.  551 

regarded  as  a  system  of  interrelated  molecules.  The  excitation  and 
propagation  of  nerve-commotion  consists  in  producing  and  continu- 
ing changes  in  the  atomic  structure  and  mutual  relations  of  these 
molecules.  In  order  to  account  for  that  "  bent,"  direction,  or  ten- 
dency to  act  in  a  certain  way,  which  all  habit  of  the  nervous  system 
presupposes,  the  internal  molecular  alteration  of  the  nervous  ele- 
ments, especially  of  the  individual  nerve-cells,  has  to  be  assumed. 
But  the  power  of  propagating  their  kind  belongs  to  these  individ- 
ual nerve-cells  ;  and  it  is  likely  that  all  the  essential  principles  of 
heredity  and  evolution  apply  to  the  exercise  of  this  power  in  the 
case  of  these  cells. 

The  biological  laws  which  control  the  nutrition  of  living  organ- 
isms also  have  an  application  to  the  nervous  elements.  The  exer- 
cise of  any  of  the  nerve-cells  or  groups  of  nerve-cells  of  which  the 
end-organ  or  the  central  organ  is  composed  tends  to  enlarge  them 
by  appropriation  of  the  nutriment  brought  to  them  in  the  blood- 
supply.  Such  nutrition,  however,  will  necessarily  be  dependent, 
for  the  special  type  which  must  characterize  its  manner  of  building, 
upon  the  acquired  molecular  character  of  the  cells  that  build  the 
new  material  into  themselves.  And  when  the  cells,  thus  enlarged 
and  molecularly  altered  according  to  the  character  and  amount  of 
their  exercise,  multiply  themselves,  their  offspring  of  new  cells  will 
necessarily  come  under  the  general  principle  of  heredity  in  its  ap- 
plication to  all  living  cells.  Accordingly,  three  things  must  be 
taken  into  the  account  when  considering  what  has  been  called 
(ineptly,  as  we  believe)  "  organic  memory,"  namely  :  (1)  The  en- 
largement of  the  single  cells  or  fibres  of  which  the  organ  is  com- 
posed ;  (2)  the  multiplication  of  these  elements  so  that  new  cells 
and  fibres  originate  under  the  laws  of  heredity  ;  (3)  the  internal 
molecular  alteration  of  the  nerve-cells  and  nerve-fibres.' 

§  18.  Furthermore,  it  is  certain  that  the  unity  and  continuity  of 
the  nervous  system  is  such,  even  with  respect  to  its  individual  cells, 
that  alterations  in  one  group  of  elements  involve  alterations  in 
other  groups.  Indeed,  it  is  much  more  difficult  to  predict  where 
such  sympathetic  alteration  will  end  than  to  affirm  that  it  certainly 
must  begin  and  proceed  to  considerable  lengths.  The  phenomena 
of  aphasia,  for  example  (see  chap.  11.,  §§  25  £f ),  indicate  how  many 
and  intricate  are  the  ways  in  which  those  elements  of  the  central 
organs  must  be  internally  connected  and  related  that  constitute  the 
physical  basis  of  the  memory  as  retentive  and  reproductive  of  the 
ideas  and  symbols  of  articulate  speech.     The  phenomena  occurring 

'  See  the  Vortrag  of  E.  Hering,  Ueber  d.  Gedjiclitniss  als  eine  allgemeine 
Function  d.  organisirten  Materie.    Wien,  1876. 


552  PHYSICAL   BASIS    OF   MEMORY. 

in  other  diseases  than  aphasia,  and  in  so-called  "  freaks  "  of  mem- 
ory, clearly  indicate  the  same  truth.  But  no  attempt  to  bring 
these  phenomena  under  any  strictly  scientific  formulas  has  hitherto 
been  rewarded  with  any  considerable  success.  By  continual  cor- 
related action  on  the  part  of  groups  and  areas  of  nervous  elements 
more  or  less  remotely  situated,  such  elements  become  in  some  sort 
associated  together  ;  being  thus  associated  together,  they  tend  to 
act  together  for  mutual  helpfulness  and  modification  (that  is,  to 
intensify,  inhibit,  or  characteristically  alter  each  other),  whenever 
either  one  is  in  any  manner  roused  to  yield  up  the  energy  it  has  in 
store. 

The  physical  basis  of  memory  as  retentive  is  therefore  laid  in 
the  habit,  or  acquired  tendency,  of  the  elements  of  the  nervous  sys- 
tem— both  as  respects  the  molecular  constitution  of  the  individual 
elements,  and  also  as  respects  the  association  of  groups  of  these 
elements  more  or  less  distant  from  each  other.  Each  element  of 
this  system,  especially  in  the  more  significant  of  its  central  organs, 
may  be  considered  as  a  minute  area  intersected  by  an  indefinite 
number  of  curves  of  different  directions  and  orders  ;  thus  a  molec- 
ular commotion  in  any  such  area  may,  according  to  its  character 
and  point  of  greatest  intensity,  run  out  into  the  system  along  any 
one  of  these  many  curves.  In  every  such  small  fragment  "  the 
whole  curve  slumbers,"  although  the  microscope  of  the  histologist 
cannot  detect  the  full  significance  of  the  fragment  or  distinguish 
it  from  similar  fragments  of  other  curves  intersecting  each  other  in 
the  same  area.' 

§  19.  The  nature  of  the  physical  basis  of  memory  considered  as 
reproductive,  under  the  so-called  laws  of  association,  is  even  more 
purely  conjectural  than  that  of  memory  considered  as  retentive. 
To  speak  of  an  excitation  as  imprinting  itself  upon  the  cerebral 
cells,  and  "perpetuating  itself  in  them  in  the  form  of  persistent 
vibrations,"  or  to  imply  that  mental  reproduction  is  only  the  weaker 
"  echo  "  of  these  vibratory  conditions,  to  persist  in  which  is  the 
mysterious  property  of  all  the  nervous  elements — as  does  M.  Luys  ^ 
— is  neither  good  physics  nor  good  psychology.  The  nature  of 
nerve-commotion,  so  far  as  we  know  anything  about  it,  is  not  such  as 
fitly  to  be  described  by  the  word  "  vibrations  ;"  and  that  the  forms 
of  nerve-commotion,  even  if  properly  described  by  this  word,  do  not 
"  persist  "  within  the  cells,  there  is  every  reason  to  believe.  Much 
more  unobjectionable  is  the  language  used  by  M.  Kibot '  to  describe 

'  A  figure  of  speech  adapted  from  Hering,  Ueber  d.  Gedachtniss,  etc.,  p. 
1.5  f.  "•'  See  The  Brain  and  its  Functions,  p.  147  f. 

^  Diseases  of  Memory,  p.  26  f. 


SO-CALLED   DYl^AMICAL   ASSOCIATIONS.  553 

the  conjectural  physical  basis  of  the  same  psychical  phenomena. 
According  to  the  hypothesis  of  this  authority,  "  determinate  associa- 
tions," or  "dynamic  affinities,"  are  formed  among  the  nervous 
elements  by  their  acting  together ;  by  repetition  these  affinities 
may  become  as  stable  as  are  the  primitive  anatomical  connections. 
Such  "dynamical  associations  have  a  much  more  important  part  to 
play  in  conscious  memory  than  in  organic  memory."  A  rich  and 
extensive  memory  is  not  a  collection  of  impressions  (for  all  such 
terms  as  "impression,"  "imprint,"  "registration,"  etc.,  are  inap- 
plicable to  the  case),  but  an  accumulation  of  those  dynamical  asso- 
ciations that  are  "very  stable  and  very  responsive  to  proper  stim- 
uli." The  recurrence  of  some  ideas  rather  than  others,  as  started 
by  this  or  that  sensuous  impression  or  other  phase  of  conscious- 
ness, would  then  depend  upon  the  character,  number,  and  strength, 
respectively,  of  the  different  "  dynamical  associations." 

§  20.  According  to  the  physiological  theory  of  memory,  forget- 
fulness,  or  loss  of  memory,  is  to  be  accounted  for  as  the  result  of 
the  process  of  dissolution.  As  says  M.  Kibot:  '  "To  live  is  to  ac- 
quire and  lose  ;  life  consists  of  dissolution  as  well  as  assimilation. 
Forgetfulness  is  dissolution,"  A  large  amount  of  such  "  forgetful- 
ness  "  must  then  be  considered  as  indispensable  to  the  exercise  of 
memory  ;  for  if  all  the  alterations  of  the  intermolecular  constitution 
of  the  nerve-cells  were  alike  conserved  and  propagated,  and  if  all 
the  dynamical  associations  among  the  different  more  or  less  remote 
groups  of  these  cells  were  equally  stable,  there  could  be  no  basis 
laid  for  specific  mid  characteristic  reproduction  of  the  images  of 
memory.  The  survival  of  any  of  these  associations  involves  the 
dissolution  of  many  others.  Under  this  general  fact  of  the  condi- 
tions of  forgetfulness  the  phenomena  of  those  sudden  losses  and 
disturbances  which  lesion  of  the  cerebral  substance  often  produces 
must  be  brought.  Temporary  forgetfulness  or  disturbance  of 
memory  may  be  assumed  to  be  connected  simply  with  such  func- 
tional derangement  of  the  cerebral  centres  as  interfei'es  with  the 
working  of  the  customary  "  dynamical  associations  "  among  the 
nervous  elements  of  which  these  centres  are  composed,  or  with 
which  they  are  regularly  connected. 

§  21.  No  good  ground  exists  for  speaking  of  any  special  organ  or 
seat  of  memory.  Every  organ — indeed,  every  area  and  every  ele- 
ment— of  the  nervous  system  has  its  own  memory.  This  view  be- 
longs to  the  very  essence  of  every  theory  which  considers  conscious 
mental  reproduction  as  only  one  form  or  phase  of  the  biological 
fact  of  "  organic  memory."  We  might  properly  speak,  then,  of  the 
■  Diseases  of  Memory,  p.  61. 


554  PHYSICAL   BASIS   OF   MEMOEY. 

memory  of  the  end-organ  of  vision  or  of  hearing,  of  the  memory 
of  the  spinal  cord  and  of  the  different  so-called  "  centres  "  of  reflex 
action  belonging  to  the  cord,  of  the  memory  of  the  medulla  ob- 
longata, the  cerebellum,  etc.  But  if  only  the  cerebral  hemispheres 
are  specially  and  directly  related  to  the  phenomena  of  conscious- 
ness, then  it  is  only  the  organic  memory  of  these  hemispheres 
which  can  be  spoken  of  as  the  physical  basis  of  our  memory.  For 
only  the  molecular  constitution  and  dynamical  associations  of  the 
nervous  elements  of  this  organ  can  immediately  determine  the 
character  of  conscious  mental  reproduction. 

Much  of  the  foregoing  language  arouses  a  protest  against  such  a 
misuse  of  psychological  terms.  The  fact  that  repeated  action  un- 
der stimulation  of  the  nerve-cells  of  the  cerebral  cortex  results  in 
a  modification  of  their  molecular  constitution,  and  in  the  establish- 
ment of  certain  tendencies  to  associated  action  among  them,  is 
doubtless  a  biological  fact.  It  is,  perhaps,  most  important  in  lay- 
ing the  physical  basis,  in  determining  the  physical  antecedents  and 
concomitants  of  memory ;  but  it  is  not  in  any  sense  a  fact  of  mem- 
ory. It  is  no  more  fitly  called  "  organic  memory  "  than  are  the 
molecular  alterations  produced  by  generations  of  use  in  the  wood 
of  an  old  Cremona.  The  changes  in  nerve-cells  are  indeed  far  dif- 
ferently related  to  memory  from  the  changes  that  take  place  in  the 
molecules  of  the  violin  ;  but  it  is  only  the  addition  of  consciousness 
to  the  whole  transaction  that  gives  us  any  right  to  characterize  it  by 
the  word  "  memory." 

§  22.  Just  as  there  is  no  such  experience  as  that  of  willing  in 
general,  so  there  is  no  such  experience  as  that  of  remembering  in 
general.  The  image  of  memory  always  possesses  certain  character- 
istic features ;  and  if  it  be  an  image  representing  the  percept  of 
some  one  of  the  special  senses,  its  features  are  determined  by  the 
nature  of  the  percept  which  it  represents.  There  is  sound  reason 
for  the  customary  form  of  speech  which  recognizes  a  good  or  bad 
"  memory  of  the  ear,"  of  the  eye,  etc.  Such  phrases  might  fitly  be 
extended  to  all  the  forms  of  sensation  and  perception ;  and,  indeed, 
to  all  the  mental  experiences  capable  of  being  represented  by  the 
images  of  memory.  It  would  be  equally  fitting  to  speak  of  a  good 
memory  of  the  fingers,  of  the  tongue,  of  the  larynx  and  other  or- 
gans of  speech,  etc.  Inasmuch  as  the  sensations  which  arise  in, 
and  the  movements  which  are  imparted  to,  all  these  periphei-al  por- 
tions of  the  body  have  their  representatives  in  certain  cei'ebral 
areas,  the  physical  conditions  of  the  images  of  memory  (the  physical 
basis  of  the  different  kinds  of  memory)  are  undoubtedly  laid  in  these 
same  areas.     There  is  no  one  place  where  memory,  par  excellence, 


PECULIAKITIES    OF   MEMORY.  555 

is  at  home  in  the  brain  ;  or  from  which  it  rules  the  different  organs 
of  expression  by  making  involuntary  or  voluntai-y  sallies  forth,  as  it 
were.  Yet  the  memory  of  any  one  thing  or  event  involves  so  many 
complex  and  closely  related  activities  of  mind — and  doubtless  also 
of  the  brain — that  it  is  impossible  to  tell  how  far  weakness  or  dis- 
turbance set  up  at  any  single  point  may  succeed  in  spreading  itself. 

As  to  the  physical  basis  for  characteristic  weaknesses  or  excel- 
lences of  memory  (such  as  the  inability  or  marked  ability  to  remem- 
ber names,  or  dates,  etc.),  and  for  those  apparent  freaks  of  mem- 
ory which  some  emotion  or  bodily  disturbance  may  produce,  little 
can  be  affirmed  with  confidence.  Where  the  mental  peculiarity  ex- 
tends to  rather  a  large  range  of  subjects,  such  as  come  under  one  spe- 
cial sense,  or  under  one  of  the  more  general  forms  of  the  operation 
of  one  sense,  the  natural  constitution  or  acquired  condition  of  the 
particular  organs  involved  may  be  assumed  to  be  peculiar.  The 
phrases,  "  a  good  ear  "  for  music,  "  a  good  eye  "  for  form,  color, 
proportion,  or  whatever  is  visible,  have  doubtless  both  a  psycho- 
logical and  a  physiological  significance.  But  what  reason  should 
exist  in  the  brain  why  some  particular  date  or  name  should  re- 
peatedly slip  away  beyond  the  power  of  attention  to  recall  it  (Forbes 
Winslow  tells  of  a  man  who,  after  a  fever,  lost  all  knowledge  of  the 
letter  F),  while  other  dates  or  names  in  which  we  have  had  little  in- 
terest cling  so  as  to  make  it  difficult  to  be  rid  of  them,  even  conject- 
ure fails  to  make  evident.  That  there  is  such  physical  reason,  how- 
ever, the  phenomena  of  aphasia,  and  of  other  diseases  of  memory',  as 
well  as  the  results  of  experimentation  upon  animals  for  the  locali- 
zation of  cerebral  function,  all  seem  strongly  to  indicate.  The  physi- 
cal reason  for  those  times  of  general  depression  or  exaltation  of  con- 
scious memory,  with  which  almost  all  jDersons  are  familiar,  is  less 
difficult  to  assign.  Such  reason  is  to  be  found  chiefly  in  the 
changes  of  character  and  quantity  suffered  by  the  blood-supply  of 
the  cerebral  areas — especially  in  their  effect  upon  the  extremely 
sensitive  nerve-cells  Avhich  abound  there. 

All  calculations  as  to  the  possibility  of  representing  all  the  in- 
dividual ideas  and  images  of  memory  by  one  or  more  nerve-cells 
and  nerve-fibres  each,  we  regard  as  wholly  useless — whether  the 
number  of  nerve-cells  in  the  cei'ebrum  be,  as  Meynert  calculates, 
600,000,000,  or  even  many  more,  as  Lionel  Beale  supposes.  Every- 
thing which  psychology  teaches  as  to  the  character  of  the  mental 
phenomena,  and  everything  which  physiology  teaches  as  to  the 
nature  of  the  cerebral  functions,  discourages  the  puerile  attempt  to 
connect  separate  mental  images  or  ideas  with  isolated  nerve-cells 
as  their  product. 


556  PIIYSTCAL    BASIS    OF    MEMORY. 

§  23.  It  will  doubtless  occur  to  thoughtful  readers  that  nothing 
which  has  thus  far  been  said  concerning  the  physical  basis  of  will 
and  memory  is,  in  any  true  sense  of  the  word,  an  explanation  of 
these  mental  activities.  In  what  sense  physiological  psychology 
can  be  said  to  explain  any  mental  phenomena  we  shall  consider 
elsewhere.  But  in  the  particular  case  of  memory,  for  example, 
none  of  the  relations  conjectured  as  probably  existing  between  the 
molecular  constitution  and  dynamical  associations  of  the  cerebrum, 
on  the  one  hand,  and  the  facts  of  conscious  experience,  on  the 
other  hand,  even  on  the  supposition  that  these  conjectured  rela- 
tions were  all  demonstrated  facts  of  psycho-physical  science,  would 
amount  to  anything  approaching  the  character  of  an  explanation. 
For  none  of  these  physical  conditions  immediately  concerns  the 
very  mental  activity  which  constitutes  the  essence  of  conscious  mem- 
ory. What  is  explained,  if  anything,  is  simply  why  I  remember 
one  thing  rather  than  another — granted  the  mind's  j^ower  to  remember 
at  all.  This  power  is  a  spiritual  activity  wholly  sui  generis,  and  in- 
capable of  being  conceived  of  as  flowing  out  of  any  physical  condi- 
tion or  mode  of  energy  whatevei'. 

The  truth  of  the  position  just  taken  may  be  enforced  (among 
other  considerations)  by  certain  conclusions  which  resulted  from 
our  psyclio-physical  study  of  perception.  In  the  study  of  percep- 
tion psycho-physics  can  do  much  toward  a  scientific  explanation. 
It  can  tell  what  qualities  of  stimuli  produce  certain  qualities  of 
sensations  ;  it  can  suggest  a  principle  relating  the  quantity  of  the 
stimuli  to  the  intensity  of  the  sensation  ;  it  can  investigate  the  laws 
under  which,  by  combined  action  of  various  excitations,  the  sensa- 
tions are  combined  into  presentations  of  sense  ;  it  can  show  how 
the  time-relations  of  the  sensations  and  percepts  in  consciousness 
correspond  to  the  objective  relations  in  time  of  the  stimulations. 
But  for  that  spiritual  activity  which  actually  puts  together  in  con- 
sciousness the  sensations,  it  cannot  even  suggest  the  beginning  of 
a  physical  explana+ion.  Moreover,  no  cerebral  process  can  be  con- 
ceived of  which — in  case  it  were  known  to  exist — could  possibly 
be  regarded  as  a  fitting  physical  basis  for  this  unifying  actus  of 
mind.  Thus  also,  and  even  more  emphatically,  must  we  insist 
upon  the  complete  inability  of  physiology  to  suggest  an  explana- 
tion for  conscious  memory,  in  so  far  as  it  is  memonj — that  is,  in  so 
far  as  it  most  imperatively  calls  for  explanation. 

Any  example  of  an  act  of  memory  will  serve  to  illustrate  the  fore- 
going truth.  Let  it  be  supposed  that  one  has  looked  for  a  few 
seconds  steadily  at  certain  pickets  of  a  fence  standing  in  the  open 
sunlight.     On  closing  the  eyes,  the  strong  positive  after-image  of 


THE   MYSTEKY    OF   MEMORY.  557 

the  object  remains  for  some  seconds  presented  to  the  mind  ;  this 
positive  after-image  is  then  succeeded  by  a  succession  of  negative 
after-images.  When  these  latter  have  subsided,  one  can  still  recall 
the  image  of  the  section  of  the  fence  seen  some  minutes  since  ;  one 
can  recall  the  same  image  the  next  day,  or  the  next  week,  or  after  an 
indefinite  length  of  time.  But  a  very  marked  difference  exists  be- 
tween that  which  is  before  consciousness  in  these  cases  of  so-called 
I'ecollection  and  that  which  was  before  consciousness  while  the  im- 
pression of  sense  was  going  though  its  various  phases  of  dying 
away.  Physiological  explanations,  having  reference  chiefly  to  the 
action  of  the  nervous  elements  in  the  retina,  may  be  given  as  to 
why  the  after-images  are  produced,  and  as  to  why  they  have  the 
order  of  succession  which  actually  belongs  to  them.  Other  physio- 
logical explanations,  having  to  do  chiefly  with  assumed  activities  of 
the  cerebral  nervous  elements,  may  attempt  the  problem,  why  the 
image  of  memory  is  fainter  than  the  original  impression  of  sense,  and 
why  this  image  rather  than  some  other  is  represented  at  a  particular 
time.  But  all  such  psycho-physical  explanation  does  not  touch, 
does  not  even  approach,  the  real  mystery  of  memory.  The  positive 
after-image  of  the  pickets  of  the  fence  is  not  the  same  as  the  per- 
cept which  preceded  it ;  nor  is  it  the  same  as  the  negative  after- 
image, or  the  images  of  memory,  which  follow  it.  Yet  all  these 
images  are  regarded  by  the  mind  as  similar  to  the  original  object  ; 
indeed,  as  standing  for  it.  How  can  they  be  regarded  as  similar 
to  one  another,  and  to  their  common  original,  when  no  two  of  them 
are  at  the  same  instant  before  consciousness  in  order  to  be  com- 
pared together  there  ?  The  very  essence  of  the  act  of  memory  con- 
sists in  the  ability  to  say  :  This  after-image  is  the  image  of  a  per- 
cept I  had  a  moment  since  ;  or  this  image  of  memory  is  the  image 
of  the  percept  I  had  at  a  certain  time — I  do  not  remember  precisely 
how  long  since. 

It  would,  then,  be  quite  contrary  to  the  facts  to  hold  that,  when 
the  image  of  memory  appears  in  consciousness,  it  is  recognized  as 
belonging  to  a  particular  original  percept  on  account  of  its  per- 
ceived resemblance  to  this  percept.  The  original  percept  does  not 
exist,  and  will  never  be  reproduced.  Even  more  palpably  false  and 
absurd  would  it  be  to  hold  that  any  similarity  of  the  impressions 
or  processes  in  end-organs  or  central  organs  explains  the  act  of 
conscious  memory.  Consciousness,  of  course,  knows  notliing  of 
such  similarity  in  impressions  and  processes  ;  knows  nothing  even 
of  the  existence  of  nervous  impressions  and  processes.  Moreover, 
we  could  never  know  two  impressions  or  processes  that  are  sepa- 
rated in  time  to  be  similar,  without  implying  this  same  inexplicable 


558  PHYSICAL   BASIS   OF   JUDGMENT. 

act  of  memory.  It  is  a  fact  of  consciousness,  on  which  all  possi- 
bility of  connected  experience  and  of  recorded  and  cumulative  hu- 
man knowledge  is  dependent,  that  certain  phases  or  products  of 
consciousness  appear  with  a  claim  to  stand  for  (to  represent)  past 
experiences  to  which  they  are  regarded  as  in  some  respect  similar. 
It  is  this  peculiar  claim  in  consciousness  which  constitutes  the  es- 
sence of  an  act  of  memory ;  it  is  this  which  makes  memory  wholly 
inexplicable  as  a  mere  persistence  or  recurrence  of  similar  impres- 
sions. It  is  this  which  makes  conscious  memory  a  spiritual  phe- 
nomenon, the  explanation  of  which,  as  arising  out  of  nervous  pro- 
cesses and  conditions,  is  not  simply  undiscovered  in  fact,  but 
utterly  incapable  of  approach  by  the  imagination.  When,  then,  we 
speak  of  a  physical  basis  of  memory,  recognition  must  be  made  of 
the  complete  inability  of  science  to  suggest  any  physical  process 
which  can  be  conceived  of  as  correlated  with  that  peculiar  and 
mysterious  actus  of  the  mind,  connecting  its  present  and  its  past, 
which  constitutes  the  essence  of  memory. 

§  24.  We  decline  to  enter  upon  the  discussion  of  a  special  physi- 
cal basis  for  the  mind's  power  to  form  generalized  concepts,  to 
combine  the  elements  of  past  experience  into  the  creations  of  in- 
vention and  art,  to  discover  laws,  and  to  reason  about  a  world  of 
reality  assumed  to  exist  ea^/ra-mentally,  or  about  the  nature  and 
order  of  the  phenomena  of  its  own  consciousness.  There  is  abso- 
lutely no  scientific  ground  on  which  to  place  such  a  discussion. 
A  physical  basis  of  the  logical  faculty,  so  far  as  it  is  a  subject  of 
either  knowledge  or  conjecture,  is  laid  in  those  general  processes 
of  the  nervous  system  that  are  correlated  with  the  elementary  forms 
of  mental  activity  upon  which  the  higher  forms  are  built,  as  it 
were,  or  which  they  presuppose.  Particularly  important  is  the 
function  of  articulate  language  in  serving  as  a  support  for  the  logi- 
cal processes.  But  that  which  is  peculiar  to  all  these  forms  of 
psychical  activities,  and  which  causes  them  to  be  spoken  of  as 
higher  and  more  distinctively  spiritual  faculties,  does  not,  as  such, 
admit  of  being  made  the  subject  of  psycho-physical  researches. 
The  attempt  to  deal  with  this  subject  psycho-physically  only  leads 
to  a  tedious  and  meaningless  repetition  of  the  phrases  and  state- 
ments which  the  psychology  of  consciousness  correctly  employs ; 
but  nothing  is  made  the  clearer  by  repeating  words  that  are  only 
applicable  to  psychical  phenomena  in  connection  with  conjectures 
concerning  related  physical  phenomena.  "  For  all  the  higher 
spiritual  faculties,"  says  Lotze,'  "  which  consist  in  judgment  of  the 
relations  of  given  conceptions,  we  neither  know  how  empirically  to 
'  Outlines  of  Psychology,  p.  141  f. 


HIGHER  SPIRITUAL   FACULTIES.  559 

demonstrate  a  definite  bodily  organ,  nor  should  we  know  how  to 
conceive  precisely  what,  that  is  of  any  use,  such  an  organ  could 
contribute  toward  the  solution  of  the  most  essential  part  of  the 
problem — that  is,  the  pronouncing  of  the  judgment  itself.  It  is 
conceivable,  on  the  other  hand,  that  these  higher  activities  might 
presuppose  the  complete  and  clear  representation  of  the  content 
about  which  the  judgment  is  to  be  passed,  and,  consequently,  also 
the  undisturbed  function  of  those  organs  which  contribute,  first,  to 
perception  by  the  senses ;  then  to  its  reproduction  and  combina- 
tion with  other  perceptions  ;  and,  finally,  to  the  appropriate  attach- 
ment of  feelings  of  value  to  each  of  them." 


CHAPTEE  XI. 

CERTAIN    STATICAL    RELATIONS    OF    THE    BODY    AND 
MENTAL  PHENOMENA. 

§  1.  The  intimate  relation  between  the  constitution  and  func« 
tional  changes  of  the  bodily  structure,  on  the  one  hand,  and  the 
character  and  course  of  the  phenomena  of  consciousness,  on  the 
other  hand,  is  most  easily  made  obvious  by  such  alterations  of  ex- 
perience as  are  connected  with  the  use  of  the  organs  of  sensation 
and  motion.  These  alterations  are  usually  sudden.  Where,  on  the 
contrary,  the  relation  of  body  and  mind  is  stationary,  or  subject  to 
only  very  slow  changes,  it  is  far  less  obvious  ;  it  may  be,  indeed, 
completely  hidden  from  our  observation.  The  relation  is  not  for 
this  reason,  however,  any  the  less  certain  and  profoundly  influential. 
Indeed,  it  is  just  those  physical  conditions  which  are  part  of  the 
unchanging  equipment  of  our  lives  that  most  surely,  though  most 
stealthih-,  determine  the  development  of  conscious  experience. 
These  are  the  influences  of  whose  very  existence  we  are  for  the 
most  part  unaware,  and  over  the  effect  of  which  we  have  compara- 
tively little  or  no  control.  Within  certain  limits,  one  can  deter- 
mine the  character  and  number  of  the  excitations  that  fall  upon 
the  end-organs  of  sense,  and  the  resulting  changes  in  the  movable 
parts  of  the  body  ;  one  can  also  regulate  to  some  extent  the  suc- 
cession of  images  of  memory  and  fancy,  and  so  the  character  and 
intensity  of  the  feelings  and  emotions  that  possess  the  field  of  con- 
sciousness. But  one  cannot  determine  one's  own  age,  or  sex,  or 
race,  including  parentage  and  prenatal  and  infantile  environment ; 
nor  can  one  choose  one's  temperament.  Yet  how  pervasive,  mighty, 
and  enduring  are  the  unobserved  influences  that  flow  into  the 
conscious  life  of  the  individual  from  age,  sex,  race,  and  tempera- 
ment! 

The  bearing  of  the  foregoing  remarks  might  be  enforced  by 
m^ny  illustrations.  No  one  is  in  need  of  technical  information  to 
assure  him  that  the  character  of  his  consciousness  is  every  instant 
dependent  upon  whether  his  eyes  are  closed  or  open.  That  we 
hear  with  the  ear,  feel  both  the  roughness  and  smoothness  and 


NATUEE   OF   POPULAR   IMPRESSIOlSr.  661 

also  the  heat  and  coolness  of  objects  with  the  skin,  taste  with  the 
mouth,  and  smell  with  the  nose  are  matters  of  experience  belonging 
to  each  moment  of  our  work-a-day  life.  The  pleasures  and  pains 
of  sense  irresistibly  demonstrate  the  dependence  of  our  mental 
states  upon  the  condition  of  the  body.  Other  common  experiences, 
although  not  arresting  attention  in  the  same  obtrusive  fashion, 
nevertheless  tend  to  confirm  the  same  impression.  The  disturb- 
ances of  consciousness  which  follow  the  altered  bodily  condition  of 
sleep  are  too  much  an  affair  of  daily  expeiience  wholly  to  escape 
attention.  The  question,  Why  are  dreams  so  queer  ?  taken  in  con- 
nection with  our  observation  of  the  abnormal  state  of  the  sleeper's 
body,  is  necessarily  answered  in  a  way  further  to  emphasize  the 
general  relation  between  bodily  and  mental  states.  Almost  every- 
one has  also  particular  times  of  experience  when  he  is  forced  into 
the  admission  that  the  physical  system  is  to  be  blamed  for  the 
altered  conditions  of  his  mental  life.  The  loss  of  a  night's  rest 
renders  attention  to  work  impossible  on  the  following  day  ;  a 
slight  fever  sets  the  train  of  memory's  images  and  fancy's  creations 
into  accelerated  and  altered  movement,  or  throws  it  into  wild  con- 
fusion ;  a  settled  melancholy  comes  as  the  obvious  result  of 
chronic  dyspepsia.  In  these  ways  the  popular  impression  that  the 
body  dominates  the  mind,  and  that  bodily  conditions  determine 
our  feelings  and  thoughts,  is  strongly  corroborated. 

But  other  phenomena  constantly  tend  to  confirm  the  other  popu- 
lar impression,  that  the  mind  dominates  the  body  and  makes  it  the 
servant  of  its  feelings  and  thoughts.  In  the  ordinary  estimate,  all 
performance  of  physical  work  by  the  body,  when  accompanied  by 
the  feeling  of  effort,  is  an  indisputable  proof  of  the  immediate  in- 
fluence of  the  mind  over  the  body.  It  is  even  more  than  this  ;  it 
is  a  proof  that  the  conscious  self,  the  ego,  is  a  source  of  physical 
energy,  which  pours  forth,  as  it  were,  into  the  limbs  and  braces 
them  to  the  appointed  task.  The  thought  of  the  aged  but  vig- 
orous French  philosopher,  who  insisted  upon  remarking  how  well 
he  carried  his  legs,  rather  than  upon  how  well  they  carried  him, 
accords  accurately  with  the  popular  impression.  All  the  cus- 
tomary language  about  looking,  listening,  recalling,  etc.,  as  dis- 
tinguished from  mere  seeing,  hearing,  and  happening  to  remem- 
ber, also  enforces  the  same  impression.  The  average  man  or 
woman,  whose  life  is  one  of  constant  toil,  is  led  to  say  with  about 
equal  frequency — "  My  limbs  are  tired,  and  /  must  stop  trying," 
or  "  /  am  tired,  but  my  limbs  must  be  made  to  go  on  with  their 
work." 

Other  phenomena  of  an  abnormal  kind  tend  to  confirm  still  fur- 
36 


562  GENERAL   BODILY   DIFFERENCEa. 

ther  the  above-mentioned  vague  popular  impression.  Among  them 
may  be  mentioned  the  wonderful  cases  of  so-called  diseases  of  mem- 
ory or  of  will,  and  of  double  personality  or  other  alienations  from 
normal  self-consciousness.  In  such  cases  strange  alterations  of  the 
modes  of  the  mind's  behavior — alterations  which  appear  to  involve 
the  suspension  or  reversal  of  some  of  those  mental  laws  and  activi- 
ties which  we  are  accustomed  to  consider  among  the  most  funda- 
mental— seem  to  be  connected  with  certain  alterations  of  the  bodily 
organs.  The  effect  of  certain  drugs,  through  the  body,  upon  the 
feelings  and  mental  train  gives  other  occasions  for  insisting  upon 
the  dependence  of  the  phenomena  of  consciousness  upon  the  state 
of  the  body.  On  the  other  hand,  hallucination,  hypnotism,  and  the 
yet  more  obscure  phenomena  of  so-called  "  mind-reading,"  as  well 
as  all  the  phenomena  to  which  modern  Spiritualism  appeals,  pi-e- 
sent  the  question  to  us  afresh  from  a  somewhat  different  point  of 
view. 

§  2.  It  requires  more  reflection  upon  wider  experience  to  origi- 
nate and  confirm  the  impression  that  all  the  characteristic  experi- 
ences of  the  individual  are  built  upon  a  solid  and  enduring  basis  of 
common  relations  which  universally  maintain  themselves  between  cer- 
tain types  of  physical  constitution  and  activity  and  certain  correspond- 
ing types  of  the  character  and  action  of  the  mind.  The  development 
of  the  child  is  ordinarily  regarded,  whether  from  the  physical  or  the 
psychical  point  of  view,  in  an  isolated  and  disconnected  way.  It  is 
perhaps  noted  that  he  has  grown  so  much  taller  or  heavier,  or  that 
certain  external  features  of  the  body  are  becoming  relatively  more 
pronounced  ;  it  is  also  noted  that  he  is  learning  to  walh,  to  talk,  to 
take  an  interest  in  certain  things  before  unnoticed,  and  to  remem- 
ber what  he  has  been  taught.  But  the  close  relations  between  the 
bodily  changes  of  advancing  years  and  the  mental  development  of 
the  child  are  not  (at  least  until  the  age  of  puberty  is  reached)  apt 
to  be  made  the  subject  of  careful  observation.  In  somewhat  the 
same  way  does  ordinary  reflection  deal  with  the  question  as  to  any 
relation  between  the  physical  and  the  mental  peculiarities  of  the 
sexes.  It  is  common  enough  to  note  that  boys  and  girls  do  not, 
even  in  selecting  and  conducting  their  plays,  act  precisely  alike. 
That  the  former  are,  as  a  rule,  taller,  heavier,  coarser,  than  the  lat- 
ter is  patent  to  all  observers.  But  that  the  absolute  and  relative 
\levelopment  of  all  the  organs  of  the  male  and  female  is  different, 
and  that  certain  sexual  peculiarities  of  perception,  feeling,  thought, 
and  action  are  constantly  related  to  this  difference,  is  something 
which  few — if  they  even  susjDCct  it — take  any  pains  accurately  to 
remark  or  describe.     Moreover,  while  almost  all  agree  that  the  psy- 


NATUEE   OF   POPULAR  IMPRESSIOlSr.  563 

chical  life  of  the  adult  male  and  female  is  distinguished  by  sexual 
peculiarities,  there  is  the  widest  diversity  of  opinion  as  to  the  pre- 
cise nature  and  range  of  these  peculiarities. 

When  the  inquiry  concerns  characteristics  of  both  mind  and 
body  belonging  to  race  and  ancestry,  the  answers  given  by  different 
observers  seem  to  lose  all  claim  to  strictly  scientific  quality.  The 
Frenchman  does  not  describe  himself  as  the  Englishman  describes 
him  ;  and  neither  one  of  the  two  can  be  expected  to  agree  with  the 
Russian  as  to  what  are  the  peculiarities  that  characterize  this  last 
type  of  the  human  species.  The  history  of  the  discussion  regard- 
ing the  kinds  and  significance  of  so-called  "temperaments,"  and 
even  regarding  the  very  existence  of  temperament,  shows  clearly 
how  uncertain  is  this  entire  field  of  research. 

Perhaps  the  most  remarkable  instance  of  firm  conviction  con- 
cerning the  general  fact  that  intimate  relations  exist  between  mind 
and  body,  accompanied  by  the  utmost  vagueness  concerning  the 
precise  nature  of  the  basis  of  such  relations,  may  be  derived  from 
the  ordinary  views  as  to  heredity.  It  is  constantly  being  remarked 
of  children  that  they  resemble  some  one  of  their  ancestors  in  one 
or  more  physical  characteristics.  But  this  remark  is  scarcely  more 
frequent  than  the  corresponding  one  with  respect  to  mental  con- 
stitution or  mental  idiosyncrasies.  Of  course  the  obvious  implication 
is,  that  we  are  to  look  to  the  laws  of  heredity  for  an  account  of  the 
origin  of  both  classes  of  qualities  ;  in  other  words,  both  physical  and 
mental  qualities  are  regarded  as  inherited.  Further  than  this  ad- 
mission ordinary  reflection  upon  experience  with  facts  of  this  order 
does  not  lead  most  men.  It  is  obvious,  however,  that  even  the 
loose  popular  impression  must  be  explained,  if  at  all,  by  insisting 
upon  much  more  numerous  and  intimate  relations  between  body 
and  mind  than  the  impression  would  seem  at  first  to  imply.  For 
how  can  ancestral  characteristics  be  transmitted,  unless  they  are 
potentially  carried  over  in  those  living  cells  from  the  two  parents 
which  actually  fuse  together  in  the  production  of  the  new  life  ;  or 
else  are  also  due  to  the  prenatal  conditions  that  control  the  nutri- 
tion of  the  infant's  body  before  it  separates  from  the  body  of  its 
maternal  ancestor  ?  But  to  admit  this  is  to  insist  upon  the  pro- 
foundest  connection  between  the  molecular  structure  and  dynam- 
ical associations  of  the  elements  of  the  physical  organism  and  the 
development  of  conscious  life.  It  is  even  to  insist  upon  the 
mysterious  fact  that  the  character  of  the  conscious  life  is  deter- 
mined in  no  small  degree  by  the  statical  peculiarities  of  the  or- 
ganism. 

§  3.  In  general,  it  may  be  said,  then,  that  while  no  doubt  exists 


564  GENERAL   BODILY   DIFFERENCES. 

in  the  popular  impression  as  to  tlie  dependence  of  the  mental  life 
upon  the  age,  sexual  differences,  and  inherited  ancestral  qualities  of 
the  bodil}'  organism,  the  greatest  uncertainty  and  vagueness  exist 
as  to  the  nature  and  extent  of  such  dependence.  When  this  kind 
of  inquiries  is  brought  to  the  tests  of  science,  it  is  found  that  all 
the  evidence  confirms  the  positive  part  of  the  ordinary  impression  ; 
but  it  cannot  be  said  that  any  substitute  for  the  uncertainty  and 
indefiniteness  of  the  popular  estimate  has  yet  been  found.  The 
reasons  for  this  failure  lie  in  the  very  nature  of  the  subject.  No 
guidance  by  the  immediate  evidence  of  consciousness  is  possible 
in  determining  the  nature  of  this  class  of  psychical  phenomena. 
What  it  is  to  will,  to  remember,  or  to  reason,  each  one  trusts  him- 
self to  know  as  a  matter  of  his  own  inner  experience.  But  the  in- 
quiries, How  are  the  mental  peculiarities  of  the  different  ages,  or 
of  the  two  sexes,  to  be  distinguished  from  each  other  ?  or.  How 
does  a  person  of  this  or  that  I'ace  or  temperament  think,  feel,  and 
act  differently  from  a  person  of  another  race  or  temperament  ?  are 
plainly  not  subjects  for  an  appeal  to  consciousness.  Few  questions 
can  be  raised,  for  example,  about  which  a  wider  diversity  of  view  is 
likely  to  be  evoked,  than  the  question  as  to  how  man  and  woman 
differ  mentally.  Yet  this  question  must  be  answered,  if  we  are  to 
have  an  answer  to  the  further  inquiry  concerning  the  correlations 
between  sexual  differences  of  organism  and  sexual  mental  differ- 
ences. 

The  difficulty  of  simply  getting  at  the  anatomical  and  physio- 
logical facts  necessary  for  an  induction  is  scarcely  less  unmanage- 
able. A  great  amount  of  careful  measurement  and  a  vast  array 
of  statistics  are  necessary  even  to  tell  how  human  beings  differ 
in  the  most  external  features,  at  different  ages  and  as  between 
the  two  sexes.  Certain  data  with  respect  to  the  height,  weight, 
relative  size  of  the  different  external  members  of  the  body,  and  of 
the  brain,  are  obtainable  ;  but  other  data  equally  desirable  are  as 
yet  unattainable.  Concerning  the  nature  of  the  physical  basis  of 
temperament  and  of  personal  idiosyncrasies  we  are  wholly  in  the 
dark. 

There  are  therefore  many  gaps  and  deficiencies  in  both  the 
physical  and  the  psychical  series.  But  where  the  members  of  both 
of  any  two  series  to  be  compared  are  in  this  condition,  the  laws  of 
their  relation  cannot  be  pointed  out.  Nothing  remains,  then,  but 
to  guide  ourselves  as  best  we  may  by  general  observation  of  the 
psychical  facts,  and  by  use  of  such  few  statistical  results  as  are 
available.  On  few  points  will  precise  conclusions  be  found  attain- 
able.     But  the  one  conclusion  of  greatest  value  concerns  the  main 


THE   PHASES    OF   LIFE.  565 

point  called  in  Question — and  tbis  is  the  general  fact  of  the  corre- 
lated action  of  the  bodily  organism  and  the  mind  as  the  subject  of 
the  phenomena  of  consciousness. 

§  4.  Certain  facts  of  general  import,  concerning  the  height, 
weight,  comparative  growth  of  the  members,  size  of  the  brain  and 
organs  of  sense,  etc,  which  characterize  the  different  Phases  of 
Life  may  be  relied  on  with  considerable  confidence.  The  struct- 
ural and  physiological  development  of  the  prenatal  human  being 
has  been  investigated  with  more  or  less  success  by  embryology 
(comp.  Part  I.,  chap.  VI. )  ;  but  scarcely  any  trustworthy  data  exist 
for  a  comparative  psychology  of  the  foetus.  It  cannot  be  held  that 
its  sentient  life  keeps  even  pace  with  the  formation  and  growth  of 
its  bodily  organs — not  even  of  those  which,  like  the  brain  and  the 
end-oi-gans  of  sense,  are  most  intimately  connected  with  the  phe- 
nomena of  consciousness.'  Large  or  elaborate  structures,  such  as 
the  lungs,  the  eyes,  the  ears,  etc.,  are  formed  under  morphological 
conditions  and  influences  with  which  we  are  only  very  imperfectly 
acquainted,  without  any  corresponding  psychical  development. 
The  brain  at  birth  is  apparently  little  different  from  the  same 
organ  a  few  weeks  later ;  but  at  this  later  period  an  important 
psychical  advance  has  been  made  through  the  activity  of  the  end- 
organs  of  sense.  This  psychical  advance  must  be  represented  in 
the  cerebral  areas  by  the  formation  of  such  molecular  changes  and 
dynamical  associations  of  the  nervous  elements  as  constitute  the 
physical  basis  of  memory  considered  as  a  retentive  and  reproduc- 
tive power. 

It  is  a  reasonable  conjecture  that  the  psychical  life  of  the  un- 
born child  consists  wholly  of  sensations  of  pressure  and  temperature, 
for  the  most  part  exceedingly  transient  and  disconnected,  occa- 
sioned by  the  stimulus  of  its  changing  conditions  and  positions  in 
the  womb  of  the  mother.  Such  a  low  grade  of  mental  experience 
— if,  indeed,  we  are  to  speak  of  prenatal  "consciousness" — can  as 
little  be  accurately  represented  by  any  conscious  state  of  the  hu- 
man adult  as  can  the  experience  of  the  animals  to  which  the  struct- 
ure and  functions  of  the  body  of  the  foetus,  in  succession,  bear  more 
or  less  of  resemblance.  About  such  a  matter  it  is  safest  to  refuse  to 
speculate.  About  one  principle,  however,  there  can  be  little  doubt 
— many  of  those  structural  and  physiological  factors  which  form  the 
most  important  and  intimate  foundation  for  the  spiritual  functions 
are  secured  only  indirectly  in  the  central  organs  through  the  culti- 
vation given  to  these  organs  by  the  use  of  the  end-organs  of  sense. 

'  Comp.  the  article  of  A.  W.  Volkmanii,  in  Wagners  Handworterb. ,  I. ,  p 
563  ;  and  the  strictures  of  Lotze  upon  it,  Medicin.  Psychologie,  p.  546  f. 


566  GENERAL   BODILY   DIFFERENCES. 

According  to  Soltmann'  and  others,  stimulation  of  the  cerebral 
areas,  considered  as  "motor"  by  Hitzig,  in  new-born  animals, 
does  not  produce  the  usual  localized  movements  (comp.  chap.  11., 
§  5  f.).  The  use  of  his  hand  by  the  child,  the  use  of  his  orgaus 
of  speech,  etc.,  educates  his  brain.  So  that  the  dependence  of 
mind  on  brain  is  not— whether  with  respect  to  the  life  before  or 
after  birth — merely  direct  and  simple,  but  also  indirect  and  com- 
plex. 

§  5.  Chaussier  considered  that  the  growth  of  the  foetus  in  length 
for  the  six  months  preceding  birth  is  regular,  and  that  it  averages 
about  54  mm.  a  month.  The  mean  height  at  birth  of  100  infants 
of  both  sexes,  measured  in  Brussels,  was  found  to  be  O.oOl  m.  for 
the  boys,  0.491  for  the  girls,*  or  about  19|  and  19^  inches  respec- 
tively. The  most  rapid  growth  of  the  child  takes  place  in  the  first 
year  after  birth  ;  this  amounts  to  an  average  of  about  2  dcm. 
(7.87  in.).  The  growth  of  the  second  year  is  about  half  of  that  of 
the  first  year  ;  that  of  the  third  year  about  one-fourth.  From  the 
fourth  or  fifth  year  until  the  age  of  puberty  the  annual  increase 
of  height  is  nearly  regular,  and  amounts  to  some  5G  mm.  During 
or  shortly  before  this  period  a  sudden  rise  in  the  curve  of  growth 
occurs  ;  but  after  this  period  the  rate  continues  to  diminish  until 
the  age  of  about  twenty-five,  when  the  full  height  may  be  regarded 
as  attained.  In  most  cases,  however,  a  slight  increase  takes  place 
between  this  age  and  fifty,  after  which  a  decrease  goes  on — esjDe- 
cially  in  extreme  old  age.  The  average  height  attained  by  the 
human  being  is  an  effect  of  race,  of  climate,  of  conditions  of  liv- 
ing and  work,  etc.  For  nine  hundred  persons,  measured  in  Brus- 
sels, ranging  from  nineteen  to  thirty  years  of  age,  the  mean  was 
1.6648-1.6841  m.^  The  average  height  of  eighty  students,  at  Cam- 
bridge, was  1.768  m.  To  express  the  facts  by  the  fraction  of  the 
whole  height  previously  attained  which  the  growth  of  each  year 
amounts  to — for  the  first  year  it  is  about  -| ;  for  the  second,  i  ; 
for  the  third,  -^^  ;  for  the  fourth,  ^V  '■>  ^'^^  t^^®  fifth,  Jj- ;  for  the 
sixth,  yig  ;  etc. 

§  6.  The  weight  of  the  newly  born  infant  is  said  by  Quetelet,^  as 
a  rule,  to  remain  about  stationary,  or  even  to  diminish  a  little,  for 
some  seven  days  after  birth  ;  it  then,  like  the  height,  grows  with 
its  maximum  rapidity  during  the  first  year  of  life.  Like  the  height, 
also,  the  weight  at  birth  varies  according  to  parentage,  prenatal 

>  Centrblt.  Med.  Wiss.,  1875,  p.  209. 

'  See  Quetelet,  Physique  Sociale  de  rHomme,  II.,  p.  13  f.     Paris.  1869. 

3  See  Quetelet,  Ibid.,  II.,  p.  19. 

^Ibid.,  IL,p.  81  £. 


PROPORTIONATE   SIZE   OF   ORGANS.  567 

conditions  as  respects  nutrition,  etc.  The  average  weiglit  of  119 
infants  weighed  at  birth,  in  Brussels,  was  found  to  be  3,055  kilo., 
or  6,735+  lbs.  avoirdupois.  With  this  the  number  3.059  kilo., 
given  in  the  "  Dictiounaire  des  Sciences  medicales,"  agrees  very 
closely.  A  year  after  bu*th  infants  of  both  sexes  have,  on  the  aver- 
age, tripled  their  weight.  Sis  years  more  are  necessary  to  double 
the  weight  attained  at  the  end  of  the  first  year  ;  and  thirteen  more 
to  quadruple  it.  At  about  the  age  of  nineteen  the  meau  weight  of 
both  sex:es  is  nearly  that  of  old  age.  The  maximum  weight  of  the 
male  is  attained,  as  a  rule,  about  forty  ;  that  of  the  female,  somewhat 
later.  At  this  time  the  weight  is  about  twenty  times  that  of  the 
infant  at  birth.  At  sixty  the  weight,  like  the  height,  begins  to  di- 
minish, Quetelet '  has  attempted  to  establish  the  empirical  law 
that,  during  the  period  of  development,  the  square  of  the  weight 
at  different  ages  is,  on  the  average,  as  the  fifth  power  of  the  height ; 
while  for  fully  developed  individuals  of  both  sexes  the  weight  is  as 
the  square  of  the  height. 

§  7.  The  proportions  which  exist  among  the  different  organs 
and  members  of  the  human  body  are  of  interest  in  this  connection. 
These  proportions  vary  greatly  for  the  different  ages  of  life,  but 
remain  nearly  the  same  for  all  individuals  (not  obviously  deformed) 
of  the  same  age.  The  parts  least  subject  to  any  departure  from 
the  normal  tyjDe  are  the  most  essential  parts.  The  height  of  the 
head  at  birth  is  about  one-half  that  attained  on  complete  devel- 
opment— or  an  average  of  about  111  mm.  (4.37  in.).  It  attains 
about  154  mm.  by  the  end  of  the  first  year,  and  173  by  the  end  of 
the  second  ;  its  growth  of  the  first  two  years  (62  mm.)  is,  there- 
fore, more  than  all  the  subsequent  growth  up  to  complete  develop- 
ment (when  it  is,  on  the  average,  228  mm.).  The  developed  head 
is  about  ^to^  oi  the  height  of  the  entire  body.  The  back  of  the  in- 
fant, however,  has  at  birth  only  about  i  its  subsequent  length ;  the 
arm,  ^  ;  the  leg,  up  to  the  place  of  bifurcation,  only  about  4. "  The 
foot  of  the  infant  (which  Avill  probably  never  afterward  appear  in 
its  natural  form  and  proportions)  is  about  -\  of  the  length  of  the 
body.  This  member  has  naturall}',  for  all  ages  and  both  sexes, 
about  the  same  length  as  the  head.  The  hand  is  about  J  of  the 
length  of  the  entire  body.  Unlike  the  head,  the  limbs  gTow  rapidly 
after  the  second  year  ;  especially  are  they  lengthened  at  the  ex- 
pense of  their  transverse  dimensions  at  the  age  of  puberty,  when 
the  bony  framework  is  outstripping  the  muscles,  as  it  were.     The 

'  Physique  Sociale,  11.,  p.  92  f. 

-  See  Quetelet,  Anthropometrie,  ou  Mesure  des  Differentes  Facultes  de 
THomme,  pp.  45  1,  194  f. 


568 


GENERAL   BODILY   DIFFEREISrCES. 


followiug  table  '  shows  the  relative  weight  of  several  internal  or- 
gans in  the  infant  at  birth  and  in  the  adult : 


Organ. 


Skeleton. . . 
Muscles,  etc 

Lungs 

Heart 

Skin 

Eye 

Brain 


Percentage  of  body-weight. 


Infant  at  birth. 


16.70 

23.40 

2.16 

.89 
11.30 

.28 
14.34 


15.35 

43.10 

2.01 

.52 

6.30 

.028 

2.37 


Ratio  of  the  two, 
the  infant  taken 
as  1. 


26 

28 

20 

15 

12 
1.7 
3.7 


§  8.  A  survey  of  the  physical  changes  which  take  place  in  de- 
pendence upon  the  age  of  the  human  being  shows  that  most  of 
them  are  only  indirectly  connected  with  the  development  of  the 
mind.  The  connection  is,  however,  scarcely  less  strongly  marked 
and  important  on  that  account.  The  changing  size  and  weight  of 
different  members  of  the  body,  both  absolutely  and  relatively,  gives 
conditions  to  the  life  of  sensation  and  motion ;  and  it  is  by  act- 
ual use  of  these  members  in  sensation  and  motion  that  the  de- 
velopment of  the  mental  powers  of  discernment,  memory,  and  will 
takes  place,  and  all  the  knowledge  of  the  spatial  qualities  and  re- 
lations of  things  is  acquired.  The  metabolic  activities  of  the  infant 
are  much  more  pronounced  than  are  those  of  the  adult ;  and  much 
of  this  metabolism  is  directed  toward  the  ends  of  construction.  To 
make  the  rapid  growths  of  the  first  years,  a  great  amount  of  food, 
representing  a  great  amount  of  potential  energy,  must  be  converted 
into  living  tissue.  More  rapid  metabolism  is  also  demanded  by  the 
necessity  of  keeping  up  the  normal  temperature  of  the  infant's 
bod}',  which  is  slightly  warmer  (3°)  than  the  body  of  the  adult, 
and  which  loses  heat  much  faster  on  account  of  its  extremely 
vascular  skin.  The  heart  of  the  infant  is,  relatively  to  its  body- 
weight  (see  table  above),  considerably  larger  than  that  of  the  adult, 
and  the  whole  circuit  of  the  circulatory  system  is  traversed  much 
quicker  (in  about  12  seconds,  instead  of  22).  Accordingly,  the  heart- 
beat is  more  frequent — namely,  about  130-140  per  minute,  falling 
off  to  about  110  in  the  second  year  and  to  about  90  in  the  tenth 
year.  The  respiration  is  also  more  frequent — it  being  about  35  per 
minute  at  first,  28  in  the  second  year,  and  26  in  the  fifth.  The 
brain  and  organs  of  sense  are  relatively  very  much  larger  in  the 
^  See  Vierordt,  Grundriss  d.  Physiologie  (5tli  ed.),  p.  605. 


SENSES   OF   THE  IISTFAI^T.  569 

infant  than  in  the  adult,  and  accordingly  .grow  less  rapidly  in  early 
life. 

Everything  in  the  infant  indicates,  therefore,  a  mobile,  flexible, 
changeable  condition  of  the  bodily  organs,  with  a  relatively  large 
development  of  the  most  important  parts  of  the  nervous  mechanism. 
Such  a  condition  is  significant  of  a  paucity  of  bodily  and  mental 
habits ;  the  lines  of  the  habitual  action  of  the  mechanism,  the 
character  and  number  of  the  dynamical  associations  among  its 
elements,  have  not  yet  been  rigidly  marked  out  and  firmly  fixed  as 
they  subsequently  are.  But  the  advanced  development  of  the  brain 
and  end-organs  of  sense  is  significant  of  the  potentialities,  as  it 
were,  rather  than  of  the  actual  experience  of  the  babe.  There  is 
difficulty  in  tracing  accurately  the  course  of  the  earliest  mental  de- 
velopment, if  by  "mental  "  we  intend  to  designate  the  jDhenomena 
of  consciousness.  The  eyes  of  the  child  during  the  first  days  of  its 
life  are  seldom  open  for  any  length  of  time.  Preyer '  asserts  that 
some  newly  born  children  move  the  eyes  with  associated  and  co- 
ordinated movements,  others  not ;  but  there  is  no  fixation  of  eyes 
such  as  indicates  an  act  of  will  in  attentive  regard  until  much  later, 
and  then  in  such  way  as  to  show  a  gradual  unfolding  of  the  power 
of  attention. 

All  newly  born  children  are  deaf  ;  the  temporary  deafness  is 
caused  by  lack  of  air  in  the  tympanum  previous  to  respiration. 
Great  individual  difierences  exist  as  respects  the  age  at  which 
children  give  unmistakable  tokens  of  having  sensations  of  sound. 
It  was  not  until  the  first  half  of  the  fourth  day  that  one  investigator 
was  satisfied  his  child  could  hear.  From  the  conditions  under  which 
the  foetus  grows  we  might  suppose  that  the  sense  of  touch,  as  re- 
gards both  pressure  and  temperature,  would  be  well  developed  in 
the  infant.  The  reflex  excitability  of  the  diffei-ent  regions  of  its 
skin  is,  however,  inferior  to  that  of  the  adult,  and  only  gradually 
approaches  it  under  the  influence  of  constant  cultivation.  Accord- 
ing to  Preyer,"  it  is  highly  probable  that  the  sensations  of  sweet, 
salt,  sour,  and  bitter  are  distinguishable  from  birth.  Taste  may 
then  be  said  to  be  "instinctive"  with  it  as  with  other  young  ani- 
mals. There  is  more  doubt  about  sensations  of  smell ;  according 
to  some  these  are  not  experienced  earlier  than  from  four  to  eight 
weeks,  but  according  to  others  they  belong  to  the  first  days  of  the 
child's  life.  It  is,  of  course,  largely  in  connection  with  the  unfolding 
of  the  activity  of  these  organs  of  sensation  and  motion  that  its  en- 
tire mental  development  takes  place. 

§  9.  After  full   maturity  has  been   attained,  and  the  period  of 

^  Die  Seele  d.  Kindes,  p.  25  f.     Leipzig,  1883.  ■  Ibid,,  p.  76. 


570  GENERAL    BODILY   DIFFERENCES. 

decline  for  the  bodily  powers  has  begun,  the  mental  jDowers  also 
are,  as  a  rule,  less  aggressive  and  acquisitive,  or  even  begin  to  de- 
cline. But  the  period  of  the  more  immediate  dependence  of  the 
latter  upon  the  sensory  and  motor  activities  of  the  bodily  organs 
has  passed  ;  the  lines  of  spiritual  as  well  as  of  corporal  habit  have 
become  firmly  drawn,  and  both  mechanism  and  mind  may  be  said 
to  contain  a  great  amount  of  stored  experience  ;  judgment  is 
trained,  and  less  liable  to  sudden  action  under  the  assaults  of  vari- 
ous forms  of  impulse.  If,  then,  no  sudden  accident  or  slow  decay 
impairs  the  cerebral  centres,  the  fullest  and  most  impressive  ma- 
turity of  the  mental  powers  may  arrive  and  continue  years  after  the 
activities  of  sense  and  motion  are  past  their  prime. 

§  10.  That  the  two  sexes  differ  in  many  ways,  as  respects  both 
physical  and  mental  characteristics,  is  an  almost  universal  im- 
pression. As  to  what  are  the  mental  characteristics  of  either  sex 
a  wide  difference  of  opinion  undoubtedly  prevails.  But  the  sta- 
tistics of  certain  physical  characteristics  of  the  sexes  are  tolerably 
complete.  Besides  the  more  obvious  bodily  differences  of  man  and 
woman,  the  two  sexes  differ  from  birth  in  average  height,  weight, 
physical  energy,  proportion  of  parts,  relative  development  of  or- 
gans, frequency  of  pulse,  respiration,  etc.  They  also  differ  in  many 
other  subtler  and  less  obvious  characteristics.  As  we  have  already 
seen  (p.  566),  the  height  of  the  male  infant  at  birth  slightly  (about 
0.01  m.)  exceeds  that  of  the  female.  The  excess  increases,  but  not 
with  perfect  regularity,  until  full  maturity  is  reached.  At  this  time 
the  height  of  the  man  may  be  given  as  1.467-1.890  m.  (about  4  ft. 
11  in.  to  6  ft.  4  in.) ;  that  of  the  woman,  1.444-1.740  m.  (about  4  ft. 
10  in.  to  5  ft.  10  in.).  The  curve  of  the  growth  of  the  two  sexes  from 
birth  onward  runs  somewhat  differently  ;  although  up  to  the  age  of 
four  or  five  the  difference  is  scarcely  perceptible.  All  the  sexual 
differences  are,  of  course,  least  pronounced  in  the  earliest  years  of 
life.  For  these  years  the  proportions  of  height  remain  about  as  1 
to  0.988  ;  at  complete  development  they  are  as  1  to  0.937,  or  about 
as  16  to  15.  But  at  sixteen  or  seventeen  years  of  age  the  growth 
of  girls  is  relatively  as  far  advanced  as  is  that  of  boys  at  eighteen 
or  nineteen.  Between  five  and  fifteen  years  the  foi-mer  make  an 
annual  growth  of  about  56  mm.,  the  latter  of  about  52  mm.' 

§  11.  The  relative  weight  of  the  two  sexes  varies  in  somewhat  the 
same  manner,  but  not  precisely,  as  their  height.  Of  119  infants 
weighed  at  birth,  in  Brussels  (63  males  and  56  females),  the  average 
weight  of  the  males  was  3.20  kilo.  (7.05  lbs.  avoirdupois)  ;  of  the 
latter,  2.91  kilo.  (6.42  lbs.).  At  the  same  age  the  male  is,  as  a  rule, 
'  See  Quetelet,  Physique  Sociale,  II. ,  p.  15  f.  ;  and  Anthropomctrie,  p.  176  f. 


GROWTH   OF   SEXUAL   DIFFERENCES.  571 

heavier  than  the  female  ;  but  although  the  boy  is  born  heaviex', 
and  in  his  earliest  years  makes  a  larger  gain  of  weight,  at  about 
twelve  the  two  sexes  have  nearly  the  same  average  weight.  The 
limits  of  weight  for  persons  normally  formed  are  about  49.1- 
98.5  kilo.  (108-217  lbs.)  for  man,  39.8-93.8  kilo.  (98-207  lbs.)  for 
woman.  Woman  attains  her  maximum  weight  several  years  later 
than  man. 

The  relative  proportion  of  the  bodily  parts  is  different  for  the  two 
sexes.  At  about  the  age  of  four  or  five  the  sexual  differences  iu 
this  regard  become  more  obsei'vable.  The  bony  framework  of  the 
boy  is  relatively  prominent,  and  the  outlines  of  the  limbs  become 
more  clearly  traced  in  a  Avay  to  conform  to  agile  and  strong  move- 
ment. Eounduess  of  limbs  and  amplitude  of  flesh  concealing  the 
framework  are  more  characteristic  of  the  girl.  At  the  age  of  puberty 
these  and  other  similar  differences  suddenly  become  more  strongly 
marked.  Careful  measurement  of  many  individuals  who  have  at- 
tained the  development  of  the  adult  shows  certain  noteworthy'  stati- 
cal differences  of  sex.  The  head,  Avhich  is  contained  about  7.4 
times  in  the  entire  height  of  the  man,,  is  contained  only  7.2  times  in 
the  height  of  the  woman ;  it  is,  then,  relatively  a  little  longer  in  the 
latter.  The  chest  of  the  adult  male  is  more  developed.  The  length 
of  the  arms  stretched  out  is  about  1.045  of  his  height ;  of  the  female, 
only  1.015.  The  relative  length  of  the  legs  is  greater  in  the  man. 
The  circumferences  of  the  different  parts  of  the  body  are  also  rela- 
tively different  in  the  two  sexes.  The  relative  step  is  as  1,000  to 
1,157;  and  the  weight  of  the  brain  as  about  1,272  to  1,424  (see 
chap.  I.,  §  4). 

There  are  also  marked  differences  between  the  sexes  in  the  forma- 
tion of  the  pelvis,  and  in  the  part  of  the  body  on  which  the  centre 
of  the  line  of  length  of  the  entire  body  falls.  The  costal  mechan- 
ism of  respiration  differs.  The  girl  of  five  breathes  with  her  ribs 
as  does  the  adult  woman.  The  pulse  of  woman  is  quicker  in  about 
the  same  proportion  as  her  height  is  less.  The  physical  energy  of 
which  the  male  is  capable,  whether  as  measured  by  liftiug  weights, 
by  pressure  with  the  hands,  or  other  ways  of  j^roducing  a  meas- 
urable mechanical  effect,  is  much  greater  than  that  of  the  female. 
This  follows,  of  course,  from  his  larger  brain  and  skeleton,  and 
from  his  superior  equipment  of  muscles.  Before  jiubert}^  the  dif- 
ference has  been  estimated  as  expressed  by  the  ratio  3:2;  after 
that  age  it  is  greater,  and  is  measui-ed  by  the  figures  9  : 5,  or  is 
perhaps  double.  The  average  boy  of  nine  or  ten  can  support  his 
own  weight  for  some  time  with  his  hands  ;  the  girl  cannot.  The 
average  man  can,  by  using  his  disjposable  energy,  lift  some  154 


572  GENEEAL   BODILY   DTFFEEElSrCES. 

kilo.  ;  the  woman  scarcely  half  as  much.'  The  metabolism  of  the 
female,  whether  measured  by  respiratory  or  other  excreta,  is  not 
only  absolutely,  but  relatively  less  ;  her  blood  is  not  only  less  in 
quantity,  but  also  of  lighter  specific  gravity,  and  contains  fewer  red 
corpuscles."  The  woman  is  more  inclined  than  the  man  to  be  "hy- 
persesthetic  "  (in  the  physiological  meaning  of  the  word) ;  this  in- 
volves a  tendency  to  many  forms  of  cramping  of  the  muscles,  to  sud- 
den secretions,  to  the  wide  spreading  of  stimulation  so  as  to  involve 
a  considerable  number  of  the  bodily  jDarts.'  Many  of  the  woman's 
sensations  are  less  sharply  discerned  as  to  their  qualitative  content, 
but  stir  up  accompanying  forms  of  feeling  with  more  energy. 

§  12.  In  the  description  of  those  mental  characteristics  of  sex 
which  undoubtedly  exist,  and  which  are  dependent  upon  or  con- 
nected with  the  foregoing  physical  characteristics,  a  great  diversity 
of  view  prevails.  We  cannot  enter  into  the  details  of  the  discus- 
sion. It  is  plain,  however,  that  the  gTeater  bulk  of  those  nervous 
and  muscular  masses  which  are  involved  in  the  conscious  life  of 
sensation  and  motion  both  implies  and  necessitates  great  differ- 
ences in  the  development  of  this  life.  But  judgment  and  decision 
are  also  involved  in  the  conscious  life  of  sensation  and  motion  ; 
they  are  dependent  upon  that  life  for  the  amount,  direction,  and 
lower  or  higher  order  of  their  development.  The  superior  strength 
of  the  chest,  shoulders,  and  hips  of  the  male,  in  lifting  and  moving 
heavy  burdens,  and  the  fitness  of  body  and  legs  for  walking  firmly 
and  running  swiftly,  cannot  fail  to  produce  a  marked  consciousness 
of  ease,  elasticity,  and  security,  both  of  posture  and  of  movement. 

Other  important  sexual  differences,  consisting  of  variations  in 
the  kind  and  amount  of  feeling — sensuous,  sesthetic,  intellectual, 
moral — and  especially  of  the  so-called  emotions,  are  undoubtedly 
connected  with  the  existence  and  development  of  those  organs 
specifically  characteristic  of  sex.  The  differences  in  circulation, 
resj^iration,  metabolism,  etc.,  are  also  the  cause  of  characteristic 
differences  in  sentiment  and  feeling.  Especially  important,  and 
even  determinative,  is  the  man's  larger  mass  of  nervous  matter  in 
the  cerebral  centres.  In  active  energy,  whether  as  given  out  on 
sudden  call  or  in  the  form  of  sustained  endurance  of  the  strain  of 
labor,  and  in  all  pursuits  and  achievements  requiring  such  energy, 
the  woman  (however  much  she  may  seem  to  be  superior  in  the 
passive  endurance  of  pain,  etc.)  can  never  compete  successfully  with 
the  man. 

^  Quetelet,  Antliropometrie,  p.  359  f. 

*  Foster,  Textbook  of  Physiology,  p.  713. 

^  Lotze,  Mediciu.  PsycLologie,  p.  559  f. 


SEXUAL   MENTAL    CHAEACTEEISTICS.  573 

Other  mental  differences  closely  related  to  the  more  obvious 
ones,  and  largely  dependent  upon  them,  are  less  obvious  and  easy 
to  demonstrate.  Our  purpose  will  be  served  sufficiently  by  citing, 
concerning  such  differences,  a  few  points  from  Lotze,'  who  has 
treated  the  whole  subject  briefly,  but  with  much  insight  and  caution. 
In  Lotze's  opinion,  woman  naturally  adapts  herself  more  easily  to 
new  conditions  of  life  ;  while  acquired  habits  have  a  stronger  hold 
on  man.  Her  characteristics  involve  a  mixture  of  the  sanguine 
temperament  and  the  sentimental  stage ;  while  varieties  of  educa- 
tion conceal  more  of  native  qualities.  This  would  seem  to  imply 
a  greater  molecular  immobility  and  stronger  dynamical  associations 
among  the  elements  of  man's  organism.  The  intellectual  capacity 
of  the  sexes,  Lotze  thinks,  differs  chiefly  or  solely  in  so  far  as 
special  emotional  interests  prescribe  the  course  of  the  intellectual 
life.  It  is  characteristic  of  masculine  philosophy  to  analyze  strik- 
ing phenomena  ;  it  is  characteristic  of  woman  rather  to  hate  analy- 
sis. Masculine  thought  depends  upon  the  conviction  that  whatever 
is  most  great  and  beautiful  in  the  world  has  its  mechanical  con- 
ditions ;  mascuhne  effort  upon  a  profound  reverence  for  general 
principles.  The  faith  of  woman  is  that  no  general  principle  or  form 
has  an  independent  value,  but  that  this  value  belongs  to  the  living 
reality  founded  upon  such  principle  ;  the  sentiment  of  the  feminine 
mind  is  devout  toward  completeness.  The  notions  of  the  two  as  to 
spatial  and  mathematical  relations,  and  their  perceptions  as  to  the 
nature  of  the  concrete  realizations  of  the  ideas  of  space  and  time, 
are  markedly  different.  In  seeking  for  some  physical  basis  for 
these  and  similar  differences — in  case  their  existence  be  once  as- 
sumed— we  are  forced  to  admit  that  any  such  known  basis  can  be 
at  best  only  indirectly  related  to  the  differences  themselves.  The 
general  truth  holds,  however,  that  certain  intellectual  differences 
are  intimately,  and  even  necessarily,  connected  with  certain  emo- 
tional differences  ;  and  that  the  latter  plainly  have,  in  many  cases, 
their  ground  in  the  organic  differences  of  the  two  sexes. 

§  13.  The  different  intellectual  and  emotional  characteristics  of 
the  different  races,  and  the  relations  of  such  characteristics  to  defi- 
nite variations  of  the  bodily  type  of  each  race  from  that  of  our  com- 
mon humanity  cannot  be  discussed  without  raising  even  more 
obscure  and  doubtful  inquiries.  If  external  influences  of  soil,  cli- 
mate, food-supply,  character  of  the  prevalent  civilization,  etc.,  have 
any  observable  influence  upon  the  type  of  the  bodily  form — and  of 
this  there  can  scai'cely  be  a  doubt — and  if  the  laws  of  heredity  are 
to  be  allowed  the  scope  and  influence  which  belongs  to  them,  the 
'  Microcosmus,  ii.,  p.  39  f.     Edinburgh,  1885. 


574  DOCTRITSTE   OF   TEMPERAMENTS. 

existence  of  both  physical  and  mental  characteristics  of  race  must 
be  admitted.  The  popular  impression  confirms  the  assumption  of 
anthropological  science.  But  there  are  few  subjects  concerning 
which  statistics  and  impressions  are  both  more  incomplete  and 
more  unsatisfactory. 

According  to  Quetelet's  conclusions,  the  proportions  of  the  aver- 
age human  body  are  such  as  to  render  it  the  type  of  manly  beauty  ; 
and  the  limits  of  these  proportions  are  the  more  fixed  and  un- 
changeable the  nearer  we  approach  to  perfection.  In  the  special 
features  of  height,  weight,  and  relative  form,  rather  than  size  of 
the  organs,  certain  differences  appear  which  belong  to  different 
peoples  and  races.  Each  people  may  be  said  to  have  its  peculiar 
type  ;  and  among  each  people  such  type  exists,  not  only  in  fact  and 
determinable  by  scientific  means,  but  as  vaguely  established  in  the 
general  appreciation.  According  to  Quetelet,'  the  principal  pro- 
portions of  the  human  figure  vary  very  little  among  different  races 
of  men.  "  The  real  differences  which  the  races  present  appertain 
to  characteristics  which  the  eye  seizes  better  than  the  compasses  ; 
in  order  to  establish  them  firmly,  an  appreciation  of  minute  differ- 
ences is  required,  and  a  tact  that  presupposes  a  long  experience  in 
such  researches.  One  can  see  the  difficulties  with  which  phrenolo- 
gists meet  in  making  numerical  estimates  of  the  characteristics  of 
the  skull ;  nothing  precise  can  be  formulated  in  this  regard  "  (comp. 
chap,  n.,  §  4).  This  conclusion  of  Quetelet  is  formulated  in  view  of 
careful  measurement,  not  only  of  many  individuals  from  the  modern 
European  jjeoples,  and  of  certain  selected  cases  among  the  North 
American  Indians,  the  Chinese,  and  the  Kaffirs,  but  also  of  Egyp- 
tian mummies,  of  Greek  statues,  and  of  other  means  for  ascertain- 
ing the  proportions  of  ancient  man. 

§  14:.  Few  impressions  are  more  firmly  fixed  than  this,  that  dif- 
ferent individuals  (at  least  among  all  the  more  highly  civilized 
peoples)  possess,  each  one,  a  characteristic  "natural  disposition." 
Such  disposition  constitutes  a  predominating  tendency  to  feel, 
think,  and  act  in  certain  forms  rather  than  others  among  the  many 
that  are  conceivable.  The  conviction  that  the  disposition  of  the 
individual  is  innate  and  inherited,  rather  than  the  result  of  training 
or  environment,  is  doubtless  due  to  the  fact  that  it  appears  with 
considerable  strength  in  childhood,  and  generally  maintains  itself 
under  great  alterations  of  circumstances,  and  against  effort,  to  the 
close  of  the  individual's  life.  The  so-called  "  disposition  "  can,  in- 
deed, be  greatly  modified,  and  even  seem  wholly  changed  ;  but  such 
modification  is  invariably  made  at  the  expense  of  greater  energy 
'  Anthropometrie,  p.  323. 


THE  THEORY  OF  DR.  GEORGE.  575 

than  is  required  to  form  and  break  those  habits  which  are  acquired 
differently  in  different  individuals  after  birth.  Moreover,  the 
modification  is  often  one  of  expression  and  povyer  of  control  rather 
than  of  dinposition. 

Patent  facts  like  the  foregoing  have  given  rise  to  the  theory  of 
Temperaments.  Curiously  enough,  the  number  four  has  usually 
been  chosen  as  suflScient  to  designate  the  kinds  or  types  of  native 
disposition,  the  varieties  of  temperament.  The  attempt  has  also 
often  been  made  to  connect  the  different  temperaments  with  a 
bodily  basis.  As  in  several  of  the  foregoing  inquiries,  so  in  this, 
our  reliance  is  mainly  placed  upon  the  correctness  of  certain  wide- 
spread but  vague  impressions.  It  is  impossible  to  classify  the  tem- 
peraments with  the  use  of  methods  required  by  strict  scientific  in- 
duction. The  individual  can  judge  of  his  own  temperament  only 
by  remembering  his  actions  and  the  states  of  consciousness  con- 
nected with  them.  But  upon  such  a  point  memory,  and  even  the 
immediate  recognition  of  consciousness,  are  but  little  trustworthy. 
Few  things  are  more  common  than  for  the  individual  quite  to  mis- 
conceive and  misinterpret  his  own  mental  states  and  tendencies. 
On  the  other  hand,  we  have  no  means  of  judging  the  temperament 
of  others  except  by  their  action — using  the  word  action  in  its 
broadest  signification.  A  large  part  of  such  judgment  is  unavoid- 
ably misjudgment.  But  notwithstanding  all  the  doubts  and  un- 
certainties which  attach  themselves  to  the  subject  of  temperaments, 
those  who  are  carefully  observant  of  their  fellows  will  continue  to 
believe  that  important  and  determining  natural  diffei'ences  exist 
among  them. 

§  15.  Some  of  the  older  treatises  on  psychology  contained  elab- 
orate discussions  of  the  doctrine  of  temperament,  in  which  many 
well  observed  facts  and  shrewd  conjectures  were  united  with  no 
little  fanciful  speculation.  This  is  to  some  extent  true  of  the  treat- 
ment (on  the  whole  admirable)  given  to  the  subject,  for  example, 
by  Dr.  Leopold  George. '  According  to  Dr.  George,  the  four  tem- 
peraments are  defined  by  the  nature  of  the  interior  relation  which 
exists  between  perception  and  the  affections  of  the  mind.  Thus 
the  greater  the  mind's  wakefulness  to  impressions,  the  greater  is 
also  its  susceptibility  to  the  feelings  of  pleasure  or  pain  which  are 
attached  to  the  impressions.  The  "  sanguine  "  temperament  is 
distinguished  by  strength  in  this  interior  relation.  But  the  greater 
the  attention  given  to  the  objects  before  the  mind,  the  greater  are 
the  emotions  of  hope  or  fearful  expectation  which  the  objects  excite  ; 
and  from  the  emphasis  being  laid,  as  it  were,  on  this  relation  the 
'  Lelirbucli  d.  Psychologic,  pp.  125-151.     Berlin,  1854. 


576  DOCTRINE   OF   TEMPERAMENTS. 

"  melancholic  "  temperament  results.  A  large  degree  of  suscepti- 
bility to  sensation  is  naturally  accompanied  by  feelings  of  attrac- 
tion or  dread  toward  the  object  of  sensation.  This  fact  forms  a 
basis  for  the  "  choleric  "  temperament.  And,  finally,  the  so-called 
"phlegmatic"  temperament  depends  upon  the  degree  of  mental 
apprehension  with  which  different  objects  are  seized,  and  the  con- 
sequent emotions  of  satisfaction  or  disgust.  The  theory  is  then 
developed  that  different  races  and  peoples  are  distinguished  by 
some  one  of  these  four  temperaments — for  example,  the  French 
are  sanguine,  the  English  melancholic,  the  Spanish  and  Italians 
choleric,  the  Germans  phlegmatic.  More  generally  still,  the  Cau- 
casian race  is  sanguine,  the  Mongolian  melanchohc,  the  Negro 
phlegmatic,  the  Malayan  choleric.  The  four  periods  of  life  cor- 
respond to  the  four  temperaments,  according  to  Dr.  George  ;  and 
this  opinion  has  undoubtedly  a  certain  basis  in  fact,  as  well  as  a 
suggestion  concerning  the  nature  of  the  physical  conditions  which 
may  possibly  underlie  the  existence  of  temperaments.  Even  dif- 
ferent species  of  animals  are,  in  the  opinion  of  this  writer,  charac- 
terized by  predominance  of  one  of  these  four  great  tj'pes. 

§  16.  Modern  psychology,  approaching  the  subject  of  temperament 
from  the  physiological  and  biological  points  of  view,  is  more  likely 
to  be  self-restrained  and  cautious  in  its  conclusions.  Accoi'ding  to 
Wundt,'  the  fourfold  division  of  the  temperaments  is  correct,  be- 
cause, in  the  case  of  every  individual,  there  must  be  a  certain  com- 
bination of  the  two  factors  of  strength  and  speed  in  all  change 
which  goes  on  in  the  mental  movements.  The  various  affections  of 
the  mind  are  therefore  classifiable  as  either  strong  and  quick  or 
strong  and  slow,  or  else  as  weak  and  quick  or  weak  and  slow. 
Choleric  and  melancholic  persons  are  inclined  to  sti'ong  affections, 
sanguine  and  phlegmatic  to  those  that  are  weak.  By  crossing 
these  two  principles  of  division  the  following  scheme  is  derived : 

strong.  Weak. 

Quick Choleric Sanguine. 

Slow Melancholic Phlegmatic. 

The  quick  temperaments  are  directed  rather  toward  the  present, 
the  slow  toward  the  future.  The  quick  require  additional  strength, 
and  the  weak  additional  time,  in  order  to  achieve  the  largest 
amount  of  work  possible  for  them.  The  choleric  and  phlegmatic 
are  temperaments  of  action  rather  ;  while  the  sanguine  and  melan- 
cholic are  temperaments  of  feeling. 

Wundt  agrees  with  the  observations  of  Dr.  George  respecting 
'  Physiologische  Ps^'chologie,  ii. ,  p.  345  f . 


THE  THEOKT   OF   LOTZE.  577 

the  applicability  of  the  conception  of  temperament  to  orders,  fam- 
ilies, and  species  of  other  animals  as  well  as  to  man.  He  '  also 
makes  the  penetx'ating  observations  that  Pessimism  generally  rests 
upon  an  individual  peculiarity  of  temperament ;  and  that  the  true 
art  of  life  consists  in  not  having  one  temperament,  but  in  combining 
them  all.  "  One  should  be  sanguine  amid  the  petty  sufferings 
and  joys  of  daily  life,  melancholy  in  the  more  serious  hours  of 
life's  more  important  events,  choleric  toward  impressions  that  fetter 
one's  profounder  interests,  phlegmatic  in  the  execution  of  the  re- 
solves that  have  been  reached." 

Lotze's  '  treatment  of  the  doctrine  of  temperaments  is  more  ex- 
tended than  Wundt's,  but  no  less  cautious  and  suggestive.  Va- 
rieties of  temperament,  as  of  all  other  innate  natural  capacities, 
appear  to  be  most  marked  under  the  conditions  of  an  advanced 
civilization.  By  the  term  "temperaments,"  according  to  Lotze,  we 
understand :  "  (1)  The  differences,  in  kind  and  degree,  of  excitability 
for  external  impressions  ;  (2)  the  greater  or  less  extent  to  which 
the  ideas  excited  reproduce  others ;  (3)  the  rapidity  with  which  the 
ideas  vary  ;  (4)  the  strength  with  which  feelings  of  pleasure  and 
pain  are  associated  with  them  ;  (5)  finally,  the  ease  with  which  ex- 
ternal actions  associate  with  these  inner  states  themselves."  The 
ancient  fourfold  division  of  temperaments  is  approved  by  Lotze 
— as,  indeed,  it  must  be  by  all  who  advocate  intelligently  any  the- 
ory upon  the  subject.  The  sanguine  temperament  is  distinguished 
by  great  rapidity  of  change  and  lively  excitability.  This  indi- 
cates a  permanent  excess  of  the  general  capacity  for  i-eciprocal  ex- 
citement among  all  the  different  psychical  states,  and  an  exces- 
sive sensitiveness  of  the  soul  to  all  external  stimuli.  It  is  natural 
in  children  and  uncivilized  tribes  ;  it  is,  on  the  whole,  advantageous 
to  the  beginnings  of  culture,  and  prevents  the  establishment  of 
narrow  notions  and  attachment  to  ideas  acquired  accidentally.  But 
adults  who  are  strongly  marked  by  this  temperament  make  the 
impression  of  immaturity,  of  being  "  grown-up  children."  For  the 
temperament  usually  called  "melancholic  "  Lotze  prefers  the  term 
sentimental.  This  temperament  is  distinguished  "  by  special  recep- 
tivity for  the  feeling  of  the  value  of  all  possible  relations,"  but  is 
indifferent  toward  bare  matter  of  fact.  Here  a  Hvely  appreciation 
of  the  harmonies  and  discords  of  surrounding  objects  may  be  com- 
bined with  little  inclination  for  hard  work  ;  a  great  variety  of 
aesthetic  feeling,  of  imaginative  activity,  may  go  with  theoretical 
vagueness  and  the  disturbance  of  an  established  sense  of  duty  by 

'  Microcosmus,  ii. ,   pp.    24   fE. ,  Edinburgh,    1885  ;    Medicin.    Psycliologie, 
560  f.  ;  Outlines  of  Psychology,  p.  137. 
37 


578  DOCTRiisrE  of  tempekaments. 

this  sesthetic  feeling.  The  sentimental  temperament  shows  itself  in 
science  among  those  who  "spend  their  ingenuity  in  constantly  de- 
vising some  new  dress  for  the  knowledge  they  have  acquired  ; "  and 
in  art  by  dealing  with  "  isolated  lyric  movements  of  emotion,"  with- 
out being  capable  of  grasping  them  and  bringing  them  together 
into  a  coherent  whole.  It  is  distinctive  of  youth  and,  in  its  most 
pleasant  form,  of  those  who  retain  a  youthful  disposition  on  into 
the  later  and  the  latest  years  of  life.  " 

The  marks  of  the  choleric  temperament  are  "  one-sided  recep- 
tivity and  great  energy  in  single  directions."  It  is  therefore  dis- 
tinguished by  diminished  susceptibility  to  excitement,  but  great 
force  and  endurance  in  reaction  when  feeling  has  once  been 
aroused.  Its  fine  effect  is  an  apparent  moral  steadiness  of  char- 
acter ;  its  uncomely  effect  is  obstinate  and  narrow  perseverance  in 
a  path  once  entered  upon,  even  when  reasons  exist  for  deviating 
from  or  abandoning  it.  Its  time  of  most  natural  development  is  in 
adult  manhood  ;  but  its  occurrence  in  a  notable  way  even  among 
children  shows  it  to  be  one  of  the  native  dispositions  of  the  mind. 
Finally,  the  phlegmatic  temperament,  which  is  the  natural  temper 
of  advanced  age,  is  distinguished  by  slightly  varied  and  slow,  but 
not  necessarily  weak,  reactions.  Sluggishness  in  youth  and  equa- 
nimity in  old  age  may  both  result  from  the  action  of  this  adjust- 
ment of  the  feelings  and  impressions  to  external  stimuli  and  the 
train  of  ideas. 

§  17.  The  permanent  common  features  of  the  foregoing  views  as 
to  the  nature  of  temperament  illustrate  sufficiently  the  real  truth 
of  the  case.  The  doctrine  as  a  whole  is  one  which  in  its  main 
principles  is  undoubtedly  required  by  the  most  wide  and  varied 
observation.  On  the  other  hand,  the  differences  in  the  details  with 
which  the  different  descriptions  are  filled  out  show  the  uncertainties 
which  belong  to  every  attempt  to  elaborate  it.  Common  impres- 
sions, producing  a  common  play  of  feeling  and  regulating  the  train 
of  associated  ideas,  belong  to  all  individuals.  But  in  each  individual 
there  is  something  characteristic  as  to  the  mode,  the  intensity,  the 
speed  with  which  these  impressions  arise  when  the  stimulus  acts, 
then  combine  with  one  another,  and  so  provoke  feeling  or  regulate 
the  ideas.  In  a  more  or  less  definite  way,  all  men  generalize  the 
various  individual  examples  and  form  them  into  classes  which 
have  necessarily  lost  that  variety  and  minuteness  of  peculiarities  that 
characterizes  the  individual  and  have  been  conformed  to  some  idea 
of  a  type.  No  real  individual  perfectly  expresses  such  a  typical 
idea.  But  especially  in  those  conditions  of  civilization  where  the 
expression  of  individuality  in  a  varied  and  impressive  way  is  pos- 


PHYSICAL   BASIS   OF   TEMPERAMENT.  579 

sible  most  individuals  are  recognized  as  conforming  more  nearly 
to  some  one  rather  than  another  of  these  types. 

§  18.  As  to  the  exact  nature  of  the  physical  basis  of  temperament 
nothing  is  known.  The  influence  of  abnormal  bodily  conditions, 
and  of  certain  diseases,  to  produce  or  alter  the  disposition  of  the 
mind  in  a  manner  resembling  temperament  would  seem  to  indicate 
that  the  original  constitution  of  the  brain  is  not  the  principal 
determining  factor.  The  nature  of  the  excitation  which  external 
stimuli  produce  upon  the  end-organs  of  sense,  the  strength  of  the 
resulting  reactions  in  the  form  of  common  feeling,  the  habitual  con- 
dition of  the  internal  and  visceral  organs  and  the  coloring  they 
impart  to  common  feeling,  seem  to  be  of  prime  importance  in  de- 
termining the  temperament.  Further  than  this  it  is  difficult  to  be 
more  specific,  even  in  conjecture.  The  fact  that  the  different  periods 
of  life  are  apt  to  be  characterized  by  a  predominance  of  one  of  the 
four  temperaments  is  not  an  argument  against  the  physical  nature 
of  the  basis  of  tempei'ament  in  general.  Certain  changes  in  the 
nature,  speed,  and  strength  of  the  reactions  derived  from  the  end- 
organs  and  the  internal  organs  of  the  trunk  necessarily  accom- 
pany the  early  development,  riper  maturing,  and  decay  of  the  bod- 
ily powers.  These  cannot  fail  to  have  a  great,  though  indirect, 
influence  upon  the  activities  of  the  cerebral  centres.  But  where  so 
much  already  said  is  so  uncertain,  we  refrain  from  adding  further 
conjectures. 


§  19.  What  has  hitherto  been  developed  in  detail  respecting  the 
relations  which  maintain  themselves  between  the  structure  and 
activity  of  the  nervous  mechanism  and  the  phenomena  of  conscious- 
ness may  now  be  summarized  in  somewhat  the  following  way.  We 
seem  warranted  in  insisting  that  the  following  five  great  groups  of 
correlations  between  body  and  mind  are  always  maintained  during 
the  mind's  conscious  existence  : 

1.  The  quality  and  intensity  of  the  sense-element  in  our  expe- 
rience is  correlated  with  the  condition  of  the  nervous  system  as 
acted  on  by  its  appropriate  stimuli.  That  the  precise  character 
and  amount  of  our  sensations  are  dependent  upon  what  and  how 
much  of  various  forms  of  physical  energy  acts  upon  the  organs  of 
sense  there  is  scarcely  need  to  say.  But  the  phenomena  which 
demonstrate  the  effect  of  attention  upon  the  sense-element  itself 
prevent  us  from  regarding  the  relation  as  only  one-sided  and  sim- 
ple. The  true  state  of  the  case  is  never  represented  by  considering 
the  sensations  as  mere  passive  impressions  depending  solely  upon 


580  COERELATIONS    OF   MIND   AlSTD   BODY. 

tbe  kind  and  degree  of  the  action  wliicli  the  stimuli  exert,  These 
sensations  depend  also  on  the  condition  of  the  mind  at  the  time 
the  stimulating  effect  of  the  excited  sensorium  is  realized  in  con- 
sciousness, and  in  terms  of  consciousness.  To  represent  the  men- 
tal condition  of  attention  as  itself  simply  and  absolutely  dependent 
upon  the  condition  of  the  centres  of  the  brain  is  to  cover  up  much 
of  our  ignorance  concerning  the  relation  of  body  and  mind  with  a 
scanty  stock  of  conjecture  in  cerebral  physiology.  There  are  many 
facts  to  countenance  the  reverse  statement — the  condition  of  the 
centres  of  the  brain  depends  upon  the  state  of  the  mind  with  re- 
spect to  attention.  For  the  present  we  content  ourselves  with  this 
expression  :  The  sense-element  in  our  experience  is  constantly 
correlated  with  the  condition  of  the  nervous  system  as  under  excite- 
ment from  its  appropriate  stimuli. 

2.  The  combination,  whether  simultaneous  or  successive,  of  our 
conscioics  experiences  is  coJTelated  with  the  combination  of  the  im- 
pressions made,  from  whatever  source,  upon  the  nervous  organism- 
That  the  number  and  form  of  the  different  sensations  composing 
any  presentation  of  sense  is  dependent  upon  the  number  and  qual- 
ity of  the  different  excitations  of  the  nervous  system  which  com- 
bine in  such  presentation  there  can  be  no  doubt.  So,  too,  does 
the  order  and  time-rate  of  the  phenomena  of  consciousness  depend 
upon  the  order  and  time-rate  of  the  separate  excitations  of  the 
nervous  system.  But  no  object  of  sense  can  be  considered  merely 
as  a  compound  of  the  elements  of  sensation  entering  into  it ;  nor  is 
the  nature  of  the  mental  product  to  be  derived  from  the  physical 
laws  according  to  which  the  different  stimulations  modify,  support, 
supplement,  or  inhibit  each  other.  A  mental  synthesis,  an  activity 
that  combines  under  different  laws  from  those  which  govern  the 
putting  together  of  stimuli  of  various  wave-forms  and  degxees  of 
intensity,  must  take  place  in  order  that  one  object  of  sense  may  be 
constructed  out  of  several  sense-elements.  Again,  the  order  in 
succession  and  time-rate  of  the  conscious  states  is  not  a  mere  copy 
of  the  order  and  time-rate  of  the  impressions  made  upon  the  ner- 
vous system.  It  is  simple  matter  of  fact  that  mental  education  in 
the  making  of  those  syntheses  which  take  place  in  all  acts  of  per- 
ception is  necessary  in  order  to  see  or  touch  extended  "  Things,'' 
as  distinguished  from  merely  having  visual  and  tactile  sensations. 
Whatever  special  form  of  activity  in  the  cerebral  centres  is  assumed 
as  the  physical  basis  of  this  mental  act  of  synthesis,  it  is  by  no 
means  certain  that  such  cerebral  activity  does  not  as  truly  depend 
upon  the  mental  act  as  the  mental  act  depends  uj)on  it.  Here 
again,  at  any  rate,  the  word  "  correlation  "  seems  best  adapted  to 


CORRELATIONS  OF  MIND  AND  BODY.        581 

express  the  connection  between  tbe  physical  basis  and  the  mental 
phenomena. 

3.  Those  phenomena  of  consciousness  which  loe  designate  as 
''memory"  and  "recollection,"  as  weU  as  the  play  of  the  repro- 
duced images  of  representation  in  general,  are  correlated  with  the 
molecular  constitution  and  tendencies,  and  with  the  so-called  "  dy- 
namical associations,"  of  the  elements  of  the  nervous  system.  It  is 
not  necessary  to  repeat  in  this  connection  what  has  already  been 
said  in  proof  of  the  fact  that  these  elements  furnish,  in  part,  the 
necessary  conditions  of  conscious  acts  of  memory  ;  and,  on  the 
other  hand,  that  the  enumeration  of  certain  physical  conditions 
throws  no  light  upon  what  is  peculiarly  mental  in  the  phenomena. 
To  say  that  memory  depends  on  the  condition  of  the  cerebral 
centres  emphasizes  the  relations  involved  in  one  class  of  facts  ;  to 
say  that  memory  depends  upon  the  conscious  act  of  attention,  both 
to  the  original  object  and  to  its  reproduced  image,  presents  the 
relations  involved  in  another  class  of  facts. 

4.  The  course  of  thought,  and  all  the  higher  forms  of  self-con- 
scious experience,  are  correlated  tcith  the  condition  of  the  cerebral 
centres.  The  dependence  of  these  conscious  mental  activities  upon 
the  quantity  and  character  of  the  blood-supply  in  the  brain,  and 
upon  the  integrity  and  unimpeded  activity  of  its  tissues,  cannot  be 
called  in  question.  Of  the  exact  nature  of  this  dependence  we  can 
form  only  a  very  inadequate  picture  ;  and  Ave  have  no  means  what- 
ever of  subjecting  this  dependence  to  a  rational  explanation.  But, 
on  the  other  hand,  many  of  our  experiences  would  just  as  certainly 
lead  to  the  conclusion  that  the  condition  of  the  cerebral  centres 
depends  upon  the  higher  forms  of  self-conscious  experience.  This 
is  true  of  the  results  of  all  our  voluntary  acts  accompanied  by 
conscious  discernment  and  choice  of  one  among  several  possible 
courses  of  action.  The  facts  of  which  we  are  sure  in  such  cases 
are  these  :  An  idea  of  something  to  be  done,  an  idea  of  the  means 
(the  parts  of  the  body  to  be  moved,  and  the  sensations  and  feelings 
of  effort  which  are  associated  in  experience  with  such  movement), 
a  fiat  of  will,  and  a  result  in  sensations  and  perceptions  showing 
that  the  movement  has  been  accomplished.  The  actual  movement 
we  trace  back,  under  the  guidance  of  physiological  facts  and  laws, 
to  the  starting  of  some  form  of  nerve-commotion  in  the  requisite 
motor  areas  of  the  cerebrum.  But  unless  we  stoutly,  and  from 
mere  prejudice,  refuse  to  acknowledge  a  possibility  of  the  mind 
exercising  any  influence  upon  the  body,  we  are  warranted  in 
saymg  that  this  nerve-commotion  in  the  cerebral  motor  areas  de- 
pends upon  the  preceding  ideas  ending  in  the  fiat  of  will  to  exe- 


582  COERELATIONS    OF   MIND   AND   BODY. 

cute  a  certain  form  of  external  motion.  At  this  stage  of  the  discus- 
sion, however,  we  prefer  to  use  the  vague  term  "  correlation  "  to  in- 
dicate the  mutual  connections  between  physical  condition  and  this 
class  of  so-called  higher  mental  phenomena.  It  has  already  been 
made  clear  that  such  connections  are  here  much  less  patent,  direct, 
and  suscej) bible  of  being  stated  in  the  form  of  general  laws  than 
are  those  of  the  first  two  classes. 

5.  The  statical  condition  of  the  body  (by  which  we  mean  all 
those  inherited  peculiarities  of  the  organism,  the  sexual  and  tribal 
bodily  characteristics,  the  corporal  constitution  as  dependent  upon 
age,  which  change  only  slowly  and  within  narrow  limits,  or  do  not 
change  perceptibly  at  all)  and  the  general  tone  or  coloring  of  con- 
scious experience  are  correlated.  Upon  this  obscure  subject  we 
may  (at  least  at  present)  wisely  decline  to  take  either  one  of  two 
extreme  and  indefensible  positions.  It  cannot  be  said  to  be  re- 
quu'ed  by  the  facts  that  all  the  phenomena  of  consciousness  should 
be  regarded  as  strictly  predetermined  by  the  constitution,  environ- 
ment, and  independent  action  of  the  corporal  elements.  The  really 
convincing  argument  for  all  such  thorough-going  organicism  is  the 
wish  to  have  it  so.  At  another  extreme  stands  the  fanciful  philos- 
ophy which  considers  the  mind  as  the  builder  of  the  body — as  in 
some  way  fashioning  to  its  own  inherent  constitution  and  uses  the 
organs  of  the  physical  mechanism.  This  conclusion,  also,  we  must 
decline  to  accept  without  further  testing.  All  the  facts,  however, 
do  obviously  impress  upon  us  the  conclusion,  how  pervasive,  inti- 
mate, varied,  and  profound  are  the  mutual  relations — the  correla- 
tions— of  the  physical  mechanism  and  the  phenomena  of  con- 
sciousness. Any  further  speculation  as  to  the  real  nature  of  this 
connection,  and  as  to  the  nature  of  the  subject  of  the  mental  phe- 
nomena— of  the  Mind — must  be  reserved,  for  the  succeeding  part  of 
our  inquiry. 


PART   THIRD. 


THE    NATURE    OF    THE    MIND. 


CHAPTER  I. 
THE   FACULTIES   OF  THE  MIND,    AXD   ITS    UNITY. 

§  1.  Up  to  this  point  in  our  psycho-physical  investigations  we 
have  been  content  to  speak  of  the  mind  simply  as  the  "subject "  of 
the  phenomena  of  consciousness.  In  other  words,  the  phenomena 
of  consciousness  may  with  equal  propriety  be  spoken  of  as  mental 
phenomena ;  for  they  are  phenomena  of,  or  appertaining  to,  what 
all  men  indicate  by  the  subject  "I"  (the  ego)  when  describing  their 
different  conscious  experiences  (comp.  p.  3  f.).  This  indefinite  and 
provisional  recognition  of  the  mind  as  an  existence  to  which  differ- 
ent states,  or  conditions,  or  modes  of  activity,  may  belong  with- 
out destroying  its  unity,  suffices  for  a  simple  description  of  the 
constitution  and  activities  of  the  nervous  mechanism,  and  of  the 
relations  between  it  and  the  phenomena  of  consciousness.  But 
psychology,  even  when  pursued  from  the  physiological  point  of 
view,  can  scarcely  be  satisfied  to  push  its  inquiries  no  farther  into 
the  natui-e  of  mind.  Psychology,  from  whatever  point  of  view  it  is 
pursued,  aims  to  perfect  a  science  of  mind.  Like  every  other 
science,  it  strives  to  discover  the  essential  nature  of  that  which  it 
investigates. 

Pains  must  indeed  be  taken  to  avoid  substituting  words  for 
things,  abstractions  for  realities.  By  the  "  essential  nature  "  of 
mind  we  mean  just  that  nature  which  is  duly  inferred  from  the 
phenomena  as  essential  to  their  rational  explanation.  But  there 
are  especial  and  unique  reasons  why  psychology  should  not  will- 
ingly desist  from  renewed  attempts  at  such  rational  explanation. 
Is  the  subject  of  the  phenomena  of  consciousness — the  so-called 
Mind — entitled  to  be  considered  as  having  unity  and  reality  in  any 
defensible  meaning  of  the  words  ?  Is  it  not  peculiarly  entitled  to 
be  considered  as  a  real  being,  with  a  permanent  and  essential  nature 
of  its  own  ?  It  is  impossible  for  human  reason  not  to  attach  the 
greatest  interest  and  importance  to  these  ultimate  psychological 
inquiries.  A  sentient  and  rational  life,  without  any  self  interest  in 
the  examination  of  its  own  permanent  characteristics,  and  of  the 
grounds  upon  which  it  rests,  would  be  an  absurdity. 


583  RELATIONS   OF   MIND   AND   BKAIN. 

§  2.  Yarious  objections  maybe  raised  against  allowing  considera- 
tions like  the  foregoing  to  apply  to  the  researches  of  that  branch  of 
psycholog}^  which  is  called  "physiological. "  It  may  be  claimed  that 
the  rational  explanation  of  the  mental  phenomena  belongs  to  Meta- 
physics rather  than  to  Physiological  Psychology.  To  a  certain  ex- 
tent the  force  of  such  objections  must  be  admitted.  They  are 
not  of  a  nature,  however,  to  debar  us  from  the  inquiries  that  are  to 
be  raised  in  the  following  chapters.  On  the  contrary,  the  result  of 
the  discoveries  made  by  starting  from  the  point  of  view  held  by 
experimental  science  is  such  as  irresistibly  to  urge  upon  us  some 
of  these  very  inquiries.  For  example,  it  has  been  shown  beyond 
doubt  that  the  construction  of  presentations  of  sense  requires  the 
activitj^  of  both  bod}^  and  mind,  considered  as  standing  in  peculiar 
relations  to  each  other  with  respect  to  the  conditions  which  they 
furnish  for  the  spatial  relations  and  spatial  properties  of  these  pres- 
entations. But  do  body  and  mind  themselves  exist  in  spatial  re- 
lations ;  and  may  the  latter  be  spoken  of  as  having  spatial  prop- 
erties ?  In  other  words  :  In  what  sense  can  we  localize  mind  in 
the  body,  or  speak  of  the  body  as  the  seat  or  organ  of  mind? 
Moreover,  as  we  observe  the  two  classes  of  phenomena  (the  organic 
and  the  mental)  the  impression  is  inevitable  that  in  some  sort  they 
keep  pace  with  each  other  in  the  order  of  development.  This  fact 
unavoidably  raises  an  inquiry  as  to  the  relation  of  the  mind  to  the 
body  with  respect  to  its  origin  and  destiny. 

As  a  matter  of  fact,  moreover,  it  is  found  that  those  who  are 
most  inclined  to  complain  at  the  introduction  of  any  "  metaphysi- 
cal "  inquiries  into  the  discussions  of  physiological  psychology  are 
quite  as  apt  as  others  to  give  grounds  for  the  same  complaint 
against  themselves.  They  themselves  rarely  escape  the  charge  of 
having  a  so-called  metaphysical  theory  of  the  soul  to  maintain. 
"With  such  complainants,  moreover,  it  is  often  fi'om  the  very  begin- 
ning a  foregone  conclusion  what  the  general  natui'e  of  that  theory 
must  be.  They  decry  metaphysics  and  advocate  a  "  psychology 
without  a  soul."  Yet  they  hold,  as  an  unalterable  but  unverifiable 
assumption,  that  psychological  phenomena  must  not  be  so  discerned 
and  interpreted  as  to  seem  to  require  for  their  explanation  an  ex- 
istence called  "a  soul." 

§  3.  In  order  to  arrive  at  any  satisfactory  conclusions  regarding 
the  essential  nature  of  the  Mind,  it  is  plainly  necessary  that  we 
should  take  our  point  of  starting  from  a  consideration  of  mental 
phenomena.  For  these  are  the  very  phenomena  for  which  an  ac- 
count is  to  be  given  ;  and  there  is  no  safe  way  of  concluding  what 
is  the  nature  of  any  reahty,  or  even  of  determining  whether  any 


j^'AULTS   OF   THE   OLD   PSYCHOLOGY.  587 

assumed  reality  actually  exists,  except  by  considering  the  phenom- 
ena which  are  attributed  to  it.  The  questions,  how  far  mental 
states  and  mental  changes  ai'e  explicable  by  referring  them  to  ante- 
cedent or  concomitant  states  and  changes  of  states  in  the  nervous 
system  ;  and  how  far  such  mental  states  and  changes  require  us  to 
assume  the  existence  of  some  other  real  being  than  the  molecules 
of  the  brain  and  spinal  cord — cannot  even  be  properh'  approached 
without  a  clear  knowledge  of  what  these  states  and  changes  in 
themselves  are.  But  the  only  way  to  know  what  mental  phenom- 
ena, as  phenomena,  in  fact  are,  is  through  observation  of  such  phe- 
nomena by  the  method  of  introspection.  We  must  then  begin  this 
particular  j^art  of  our  general  discussion  by  changing  for  the  time 
our  point  of  view. 

Much  fault  has  been  found  of  late  with  the  failures  of  the  so- 
called  "  old  "  psychology.  It  has  often  been  explained  at  length 
that  these  failures  were  largely  due  to  its  wrong  method  ;  and,  as 
is  well  known,  its  method  was  almost  exclusively  the  method  of  in- 
trospection or  self-consciousness.  The  exclusive  use  of  this  method 
resulted  in  confining  the  efforts  of  psychology  very  largely  to  the 
rather  barren  task  of  classifying  the  different  kinds  of  mental  activ- 
ities, and  of  discussing  what  so-called  "faculties  "  must  be  assumed 
to  belong  to  the  mind  in  order  to  account  for  so  many  kinds  of 
activities.  Now,  classification  of  phenomena  is  certainly  one  im- 
portant part  of  the  work  of  every  science  ;  nor  should  it  be  forgot- 
ten that  much  of  the  more  recent  progress  in  psychology  is  due  to 
previous  painstaking  observations  of  mental  phenomena — resulting 
in  their  classification — from  the  purely  introspective  point  of  view. 
Classification,  however,  is  not  explanation  ;  and  the  "  faculties " 
into  which  the  "  old  psychology  "  divided  the  mind  were  too  often 
mere  names  that  repeated  the  bare  fact  of  the  observer  having  suc- 
ceeded, to  his  own  satisfaction,  in  classifying  the  phenomena.  It 
is  demanded,  however,  in  order  to  make  real  progress  in  psychology 
as  a  science,  that  the  correlations,  under  precise  and  definite  laws,  of 
the  mental  phenomena  with  one  another  and  with  the  events  which 
happen  in  external  nature  shall  be  ascertained.  Nevertheless,  even 
after  adopting  this  view  of  the  problem  we  cannot  dispense  with 
the  method  of  introspection  ;  for  we  have  no  other  way  of  ascer- 
taining what  ar'e  the  phenomena  that  require  exiDlanation.  If  the 
further  question  be  raised,  What  is  the  real  nature  of  that  subject 
of  the  mental  phenomena  popularly  spoken  of  as  the  mind?  we 
surely  cannot  approach  the  answer  to  this  question  without  calling 
attention  to  the  nature  of  the  phenomena  themselves. 

So  far  as  the  necessities  of  the  present  discussion  are  concerned, 


588  RELATIONS   OF   MIND   AND   BRAIN. 

it  may  be  said  that  there  are  two  rival  and  contrary  ways  of  reply- 
ing to  the  general  inquiry  into  the  nature  of  the  Mind.  One  of 
these  denies  that,  in  order  to  account  for  naental  phenomena,  we 
need  assume — much  less  are  able  to  prove — the  existence  of  any 
reality  other  than  the  material  substance  of  the  living  and  active 
nervous  system  (especially,  or  wholly,  of  the  brain).  The  other, 
on  the  contrary,  claims  that  no  explanation  of  mental  phenomena 
is  possible  without  referring  them  to  a  non-material  or  spiritual 
entity  as  the  real  subject  or  gTound  of  them  all.  Both  of  these 
ways  of  explanation  admit  of  various  modifications.  The  former, 
as  held  by  its  different  advocates,  has  used  different  terms  to  set 
forth  the  relation  in  which  it  believes  that  the  phenomena  of  con- 
sciousness stand  to  the  states  and  activities  of  the  brain.  The  lat- 
ter, also,  has  by  no  means  always  been  self-consistent  in  its  advo- 
cacy of  the  unique  and  independent  character  of  the  subject  of 
mental  phenomena.  Even  the  power  of  immediately  penetrating 
in  consciousness  the  secret  of  its  own  interior  nature  has  sometimes 
been  claimed  for  the  mind.  The  former  of  the  foregoing  views,  in 
whatever  particular  shape  it  may  occur,  has  customarily  been  re- 
garded as  essentially  the  "materialistic,"  and  the  latter  as  the 
"  spiritualistic,"  theory  of  the  human  mind.  A  third  view,  which 
regards  both  the  so-called  "brain"  and  the  so-called  "mind"  as 
merely  phenomenal  aspects  of  some  one  reality  that  is  like  neither, 
but  manifests  itself  in  both,  requires  for  its  discussion  so  much  of 
subtle  metaphysics,  and  is  so  foi-eign  to  all  the  scientific  material 
with  which  we  have  thus  far  been  dealing,  that  it  is  for  the  present 
passed  by  with  a  bare  allusion. 

§  4.  In  the  remaining  part  of  our  discussion  we  shall  be  chief- 
ly occupied  with  considering  which  one  of  the  two  theories  just 
stated  best  accords  with  all  the  facts.  These  facts,  which  are  to 
test  the  theory,  are  facts  of  the  nervous  mechanism,  and  of  the 
correlations  between  this  mechanism  and  the  phenomena  of  con- 
sciousness. The  question  before  us  may  then  be  stated  in  the 
following  provisional  form :  Do  the  phenomena  of  consciousness 
require  for  their  explanation  nothing  more  than  a  statement  of 
those  changes  in  the  material  mechanism  with  which  they  are  obvi- 
ously correlated  ;  or  do  they  also  require  the  assumption  of  one 
real  and  non-material  being  as  the  subject  and  ground  of  them  all? 
To  repeat  a  remark  already  made,  the  approach  to  this  question 
must  be  through  the  introspective  study  of  mind  ;  for  only  such 
study  can  tell  us  what  the  phenomena  of  consciousness  actually  are. 

§  5.  It  is  so  obvious  as  scarcely  to  need  or  admit  of  debate,  that 
mental  phenomena  are  not  identical  with  the  changing  conditions 


CONSCIOUSNESS   AND   NERYE-COMMOTION.  589 

and  activities  of  the  nervous  system.  However  our  states  of  con- 
sciousness may  be  related  to  the  states  of  the  brain — even  if  the 
former  are  absolutely  and  without  exception  dependent  upon  the 
latter — the  two  are  certainly  not  the  same.  What  the  exact  states 
of  the  brain  are  with  which  any  of  the  mental  states  are  correlated 
we  know  only  very  imperfectly  and  by  remote  conjecture.  But  so  far 
as  we  do  know  anything  about  the  particular  molecular  activities 
of  the  central  nervous  system  which  are  most  directly  connected  with 
the  phenomena  of  consciousness,  they  do  not  differ  essentially  from 
other  molecular  activities  of  this  system  not  thus  connected  with 
consciousness.  The  chemical  constitution  and  structural  form  of 
the  nerve-fibres  and  nerve-cells  of  the  brain  do  not  differ  from 
those  of  the  spinal  cord  in  any  such  respect  as,  of  itself,  to  account 
for  the  difference  in  the  relations  in  which  the  two  stand  to  con- 
scious mental  states.  They  do  not  so  differ  even  from  the  mole- 
cules which  enter  into  the  living  plant  or  animal  of  much  lower 
species,  mentally,  than  man.  It  is  a  surprise,  from  which  scientific 
investigation  can  never  recover,  to  find  that  the  connection  between 
our  sensations,  mental  images,  and  vohtions  and  the  peculiar  ma- 
terial constitution  and  functions  of  the  cerebral  mass  of  nervous 
matter  should  be  so  intimate  as  it  undoubtedly  is.  The  foregoing 
fact  shows  that  it  is  quite  impossible  to  regard  the  two  classes  of 
events — the  molecular  changes  of  the  central  nervous  mass  and  the 
happenings  of  our  conscious  expeiience — as  one  and  the  same. 

All  physical  events  are  modes  of  motion — alterations  in  the  re- 
lations of  the  material  atoms  or  masses  to  each  other  in  space. 
This  is  as  true  of  the  human  brain  as  it  is  of  the  clod  of  the  valley. 
Its  atoms  cannot  be  conceived  of  as  doing  anything,  so  long  as  they 
remain  material  atoms,  that  does  not  essentially  consist  merely  in 
changing  their  relations  in  space  to  other  mateiial  atoms.  This 
is  the  activity  which  chemistry  supposes  to  be  continually  taking 
place  as  the  work  of  nutrition  and  depletion  in  the  nervous  cen- 
tres accompanies  the  process  of  thought ;  this  is  what,  as  general 
"nerve-physiology "  rightfully  conjectures,  occurs  when  any  form 
of  stimulus  acts  upon  the  afferent  nerve  through  the  end-organs 
of  sense,  and  corresponding  states  of  sensation  arise  in  the  mind. 
But  the  conscious  process  of  thinking  is  not  the  change  in  the 
chemical  constitution  of  the  nervous  mass  ;  the  conscious  sensa- 
tions are  not  the  wave-like  movements  of  nerve-fibres  and  nerve- 
cells.  It  is  not  simply  true  that  to  identify  these  two  kinds  of 
phenomena — phenomena  of  the  motion  of  material  atoms  and 
j)henomena  of  change  in  mental  states — is  difficult  for  the  average 
mind,  but  attainable  by  the  scientific  observer ;  it  is  rather  true 


590  EELATIONS   OF   MIND   AND   BRAIN. 

that  no  mind  can  frame  any  intelligible  idea  of  what  could  be 
meant  by  identifying  the  two. 

Moreover,  the  history  of  investigation  shows  that  a  man  may  be 
highly  trained,  both  in  the  observation  of  the  phenomena  of  the 
animal  body  and  of  his  own  self-conscious  mind  (for  example, 
Ai'istotle),  without  even  suspecting  the  important  relation  which 
exists  between  the  latter  and  the  cerebral  mass.  Indeed,  there  is 
no  distinction  which  all  men  are  compelled  to  make  more  clearly 
than  that  between  their  own  conscious  states  and  the  changing  con- 
ditions, by  way  of  motion,  of  the  masses  and  molecules  of  matter. 
All  theory  which  assumes  the  possibility  of  idenlifyhig  molecular 
motions  of  brain-atoms  with  the  shifting  forms  of  mental  experi- 
ence, or  attempts  to  set  forth  the  peculiar  nature  of  the  latter  by 
simply  stating  the  conjectured  laws  which  control  the  former,  in- 
creases the  general  confusion  which  tends  to  surround  the  whole 
subject. 

§  6.  Furthermore,  it  is  not  easy  to  see  what  could  possibly  be 
meant,  that  is  worth  serious  consideration,  by  speaking  of  the  phe- 
nomena of  consciousness  as  the  jjrodud  of  the  brain.  By  the  word 
"product"  we  ordinarily  understand  the  new  form  into  which  a 
material  substance  has  been  thrown  by  the  action  upon  it  of  some 
machine  or  mechanism.  Thus  we  call  certain  secretions  of  the  body 
the  "pi'oduct"  of  the  tissues  where  they  are  secreted  in  somewhat 
the  same  way  as  that  in  which  we  speak  of  the  products  of  the 
field  or  of  the  loom.  The  function  of  the  living  molecular  mech- 
anism of  which  certain  tissues  consist  is  exercised  in  producing 
from  the  pabulum  brought  to  them  by  the  blood  the  secretions  of 
gastric  juice  and  bile.  To  speak  of  mental  states  and  processes  as 
the  "  jDroduct "  of  the  nervous  mass  of  the  brain,  in  any  sense  of 
the  words  corresponding  to  that  which  we  rightly  apply  to  the 
various  secretions  of  the  body,  involves  us  at  once  in  the  grossest 
absurdities.  The  secretory  product  of  the  brain  is  the  fluid  found 
in  certain  of  its  cavities  ;  its  nutritive  product,  so  to  speak,  is  the 
new  nervous  tissue  which  is  constantly  being  formed  from  the 
blood  by  that  activity  of  reproducing  its  own  kind  which  this  tis- 
sue has  in  common  with  other  living  tissues.  But  this  fluid  and 
these  newly  produced  molecules  or  nerve-corpuscles  in  the  brain 
are  in  themselves  no  more  like  mental  processes,  and  no  more  to  be 
identified  with  such  processes,  than  are  the  tears  that  flow  from  the 
tear-ducts  or  the  pus  that  exudes  from  a  wound.  In  so  crass  a 
way  of  speaking  it  is  diflficult  to  distinguish  what  can  properly  be 
meant  by  comparing — under  the  term  "product" — the  relation  of 
conscious  sensation  and  thought  to  the  brain  with  the  relation  of 


CO'lSrSCIOUSNESS   AND   NEEVE- COMMOTION-.  591 

the  gastric  juice  to  the  stomach  or  of  the  pancreatic  juice  to  the 
pancreas. 

There  is  another  and  more  plausible  use  of  the  word  "product'' 
to  describe  the  connection  between  the  nervous  matter  of  the  brain 
and  the  phenomena  of  consciousness.  When  a  system  of  material 
molecules  is  acting  under  relations  to  each  other  which  are  deter- 
mined by  their  constitution,  arrangement,  and  environment,  we  may 
speak  of  the  constantly  new  relations  which  they  assume  as  the 
'product  of  their  previous  constitution  and  arrangement,  and  of 
whatever  influences  act  upon  them  from  material  molecules  outside 
of  the  system  (the  environment).  Thus  the  functional  activity  of 
the  nervous  centres,  the  complex  and  interacting  nerve-commotions 
of  the  brain,  might  be  regarded  as  the  product  of  the  matter 
constituting  these  centres.  This  manner  of  speaking  has  certain 
marked  advantages.  It  emphasizes  the  merely  mechanical  point  of 
view.  It  insists  upon  the  valid  assumption  that  the  account  of 
every  change  that  arises  in  the  material  particles  out  of  which  the 
brain  is  composed  must  be  sought  for  in  the  previous  constitution 
and  arrangement  of  those  same  particles  as  acted  upon  by  stimuli 
either  external  or  internal  to  the  whole  brain-mass. 

Let  us  suppose,  for  the  sake  of  illustration,  an  incredible  increase 
in  our  powers  of  observation.  Let  us  suppose  that  it  were  possible 
with  the  microscope  to  discern  the  exact  chemical  constitution  of 
every  molecule  of  the  nervous  substance  of  the  brain,  to  Avatch  the 
motion  of  all  the  atoms  composing  these  molecules  as  chemical 
changes  take  place  or  as  waves  of  nerve-commotion  in  infinite  va- 
riety move  hither  and  thither  among  its  countless  nerve-fibres  and 
nerve-cells.  All  this  would  be  in  itself  absolutely  nothing  more  than 
an  expansion  under  the  eye  of  the  observer  of  what  he  sometimes 
sees  in  somewhat  grosser  form — for  example,  in  the  amceba — and 
of  what  he  infers  is  constantly  taking  place  in  every  kind  of  nervous 
tissue.  The  status  of  the  system  of  moving  molecules  at  each  in- 
stant is  to  be  explained — so  far  as  explanation  is  possible — from  its 
status  at  the  preceding  instant,  in  connection  with  any  influences 
bi'ought  to  bear  upon  it  from  the  outside.  Moreover,  all  such  out- 
side influences,  so  far  as  they  are  of  a  physical  sort,  are  nothing  but 
modes  of  the  molecular  activity  of  other  material  particles.  Looked 
at  in  this  way,  the  product  of  the  brain  is  the  molecular  activity  of 
the  brain.  That  is  to  say,  the  function  of  this  unique  system  of 
molecules  is  to  be  constantly  in  motion,  in  the  form  of  activity 
which  we  have  already  examined  as  "nerve-commotion." 

But  if  the  foregoing  statement  be  admitted,  how  does  it  help  us 
in  the  least  to  understand  the  phenomena  of  consciousness  regarded 


592  EELATIONS   OF   MIND   AND   BRAIN. 

as  the  product  of  the  brain  ?  In  order  to  hold  that  mental  phe» 
nomena  are  related  to  the  substance  of  the  brain,  in  the  same  way 
as  that  in  which  the  nerve-commotions  or  molecular  changes  are 
related  to  the  same  substance,  we  must  identify  mental  phenom- 
ena with  molecular  changes.  But  we  have  already  seen  that  it  is 
impossible  to  identify  the  two  classes  of  phenomena,  as  phenomena. 
The  phenomena  of  nerve-commotion  may  be  regarded  as  the  prod- 
uct of  the  nervous  mass  in  which  they  occur  ;  that  is,  they  may 
be  attributed  to  the  constitution  and  arrangement  of  the  molecules 
which  compose  this  mass,  as  showing  what  the  mass  can  do.  But 
the  phenomena  of  consciousness  cannot  be  regarded  as  the  product 
of  the  same  nervous  mass  in  any  similar  meaning  of  the  word 
"product." 

§  7.  Yet  another  unsatisfactory  way  of  regarding  the  relation 
between  the  brain  and  conscious  mental  phenomena  requires  a 
more  detailed  and  careful  consideration.  Everything  in  our  pre- 
vious examination  has  tended  to  show  that  the  molecular  changes 
which  go  on  in  the  brain,  whether  they  are  occasioned  by  afferent 
impulses  that  oi'iginate  in  the  application  of  stimuli  to  the  end- 
organs  of  sense,  or  by  the  modified  amount  and  quality  of  the  blood- 
suppl}^  are  not  only  regular  antecedents,  but  true  causes  of  what 
takes  place  in  the  mind.  All  the  second  part  of  this  treatise  was 
occujDied  in  pointing  out  the  different  classes  of  such  relations 
between  physical  antecedents  and  consequent  mental  phenomena. 
[The  objections  Avhich  are  ordinarily  urged  against  speaking  of 
physical  changes  as  the  cause  of  the  phenomena  of  consciousness 
will  be  raised  and  answered  later  on.] 

It  is  plain  to  every  unprejudiced  mind  that,  in  some  valid  sense, 
changes  in  the  condition  and  activity  of  the  substance  of  the  brain 
are  sjDecially  related  to  certain  of  the  shifting  phenomena  of  con- 
scious mental  life.  From  this  admission,  which  is  enforced  by  the 
entire  study  of  Physiological  Psychology,  the  temptation  is  strong 
to  proceed  at  once  to  the  completion  of  an  apparently  simple  and 
comprehensive  theory.  This  theory  claims  thata/^  mental  phenom- 
ena, whatever  their  varied  characteristic  shading,  have  exact  equiva- 
lents, as  it  were,  in  specific  forms  of  the  nerve-commotion  of  the 
living  brain.  Every  such  phenomenon,  therefore,  is  only  the  man- 
ifestation of  what  has  previously  taken  place,  or  is  simultaneously 
taking  place,  in  the  physical  molecular  structure  of  the  nervous 
centres.  To  employ  a  figure  of  speech — for  every  state  and  action 
of  the  so-called  mind  in  consciousness,  that  collection  of  nerve- 
fibres  and  nerve-cells  which  we  call  the  brain  exacts  a  payment 
in  some  special  kind   of  coin.     For  example,  with  the  molecular 


CEEEBRAL   AND   MENTAL   COMBINATIONS.  593 

chaiages  in  the  substance  of  the  brain  which  may  be  designated  A, 
B,  C,  D,  etc.,  the  mental  states  called  a,  ^,  y,  8,  etc.,  are  uniformly 
and  necessarily  joined  ;  and  with  the  combination  of  molecular 
changes  which  may  be  described  by  A  4-  B  +  C  +  D,  etc.,  the 
mental  states  a  +  /3  +  y  +  S,  etc.,  are  as  uniformly  and  necessarily 
joined.  When  the  molecular  changes  recur  in  a  fainter  or  modi- 
fied form,  as  A',  B',  C,  D',  then  there  must  be  a  recurrence  of  the 
corresponding  mental  states,  only  in  fainter  form,  as  a',  (i\  y',  8'. 
Finally,  it  is  without  exception  true — so  this  theory  holds — that 
nothing  happens  in  the  mind  by  way  of  conscious  sensation,  pres- 
entation of  objects  of  sense,  ideation,  reproduction  of  mental  im- 
ages, and  higher  aesthetic  feeling  or  intellectual  processes  or  choice, 
w^hich  does  not  find  its  only  real  explanation  in  the  equivalent 
changing  states  of  the  nervous  system. 

§  8.  Our  first  impression  on  considering  the  foregoing  way  of  ac- 
counting for  mental  phenomena  is  that  of  a  certain  surprising  audaci- 
ty. The  theory,  standing  on  a  slender  basis  of  real  fact,  makes  a 
leap  into  the  dark  which  carries  it  centuries  in  advance  of  where 
the  light  of  modern  research  is  now  clearly  shining.  Physiological 
Psychology,  as  we  have  been  compelled  to  regard  it,  has  been  seen 
to  be  encompassed  with  difficulties  at  every  step  ;  and  some  of 
these  difficulties  appear  absolutely  insurmountable.  It  has  achieved 
its  greatest  triumphs  in  giving  a  physical  and  physiological  expla- 
nation of  the  variations  in  the  quantity  and  quality  of  sensation, 
and  of  the  time-rate  of  the  simpler  mental  processes.  But  even  in 
these  domains  of  greatest  achievement  it  is  found  that  almost  every- 
thing needed  for  an  exact  science  of  the  relations  of  the  molecular 
changes  in  the  substance  of  the  brain  and  the  changes  in  states  of 
consciousness  is  lamentably  deficient.  In  the  first  place,  little  prog- 
ress has  been  made  in  framing  a  theory  of  the  nature  of  the  phys- 
ical changes  themselves.  Physical  science  is  not  as  yet  able  to  deal 
with  the  phenomena  of  nervous  action,  as  shown  even  by  a  single 
living  nerve  with  a  muscle  attached  when  acted  upon  by  any  one 
form  of  external  stimuli ;  how  much  less,  then,  with  that  vast  com- 
plex of  nerve-fibres  and  nerve-cells  which  constitutes  the  human 
brain  !  As  to  purely  physical  explanations  of  the  variations  in  the 
quantity  of  sensations  we  are  also  in  great  doubt.  No  adequate 
means  exist  for  measuring  accurately  the  changes  in  the  amount  of 
all  the  stimuli  which  act  on  the  end-organs  of  sense.  We  have  less 
knowledge  of  the  laws  which  regulate  the  amount  of  excitation  set 
up  in  these  organs  by  changes  in  the  amount  of  stimuli;  and 
scarcely  any  real  knowledge  at  all  of  what  molecular  changes  take 
place  within  the  central  organs  when  the  afferent  nerves  have  stirred 
38 


594  MIJSD   AS   CONSCIOUS   BEING. 

them  to  their  cliaracteristic  action.  Hence  Fechner's  laws,  con- 
sidered as  merely  empirical  statements  of  relations  between  the 
amounts  of  certain  external  stimuli  and  our  judgments  under  ex- 
traordinary conditions  as  to  how  much  we  are  affected  thereby,  are 
readily  disputed.  But  considered  as  setting  forth  the  essential  re- 
lations which  exist  between  the  physical  changes  in  the  brain  and 
the  intensities  of  the  resulting  mental  changes  they  are  quite  inde- 
fensible. Moreover,  the  amount  of  our  being  affected,  the  quan- 
tity of  the  sensation  which  results  from  the  application  of  physical 
stimulus,  can  be  determined  only  by  the  judgment  of  the  same 
consciousness  which  is  affected  with  the  sensation.  But  judgment 
itself  is  a  form  of  mental  phenomena  for  the  essential  part  of 
which  no  physical  equivalent  can  be  discovered  or  even  conceived 
of. 

What  has  just  been  said  concerning  our  inability  to  give  a  com- 
plete physical  explanation  of  variations  in  the  quantity  of  sensa- 
tions applies  with  equal  force  to  their  qualities  and  time-relations. 
But  even  if  the  whole  field  of  sensation,  as  respects  the  amounts, 
kinds,  and  order  in  time  of  its  phenomena,  were  already  covered  by 
such  purely  physical  explanation  as  refers  them  wholly  to  changes 
in  the  molecular  condition  of  the  brain,  the  above-mentioned  theory 
would  by  no  means  be  established.  For  in  investigating  the  corre- 
lations which  undoubtedly  exist  between  the  nervous  mechanism 
and  the  phenomena  of  consciousness,  it  is  found  that  some  of  these 
phenomena  imply  activities  of  the  mind  which  do  not  admit,  in  any 
sense  of  the  word,  of  being  thus  correlated.  For  an  example  upon 
this  point,  we  may  refer  to  what  was  said  (Part  11. ,  chapters  VI.  and 
Vn.)  as  to  a  mental  synthesis  being  implied  in  the  formation  of  all 
presentations  of  sense.  "  Things  "  are  not  mere  loose  aggregates 
of  sensations.  They  are  the  results  of  mental  synthetic  acts,  the 
laws  of  which  cannot  be  attributed  solely  to  the  various  ways  in 
which  the  physical  molecules  of  the  brain  are  made  to  move  by  the 
action  of  stimuli  reaching  them.  Let  it  be  admitted  that,  with  in- 
creased information,  we  should  find  the  scale  of  varieties  in  the 
kinds  of  mental  phenomena  called  sensations  corresponding,  point 
for  point,  to  the  scale  of  varieties  in  the  manner  of  the  motion  of  the 
waves  of  nervous  excitation.  Let  it  also  be  admitted  that  the  scalp 
of  the  changes  in  the  intensities  of  mental  phenomena,  that  are  of 
the  same  kind,  corresponds  with  equal  exactness  to  the  scale  of  the 
changes  in  the  vibratory  swing  of  these  waves.  Let  it  be  still 
further  admitted  that,  whenever  any  presentation  of  sense  occurs, 
there  exists  a  kind  and  amount  of  various  excitations  simultane- 
ously effected  in  the  brain  which  corresponds  exactly  to  this  par- 


NATUKE   OF   ALL    "THINGS."  595 

ticular  presentation  of  sense.  The  mere  congeries  or  common 
occurrence  of  such  sensations,  as  the  necessary  result  of  the  exci- 
tations of  the  brain,  does  not  constitute  a  real  "  Thing,"  Each 
"thing"  implies,  not  simply  a  vast  number  of  moving  physical 
molecules,  on  the  kind  and  amount  of  whose  motion  the  phenomena 
of  conscious  sensation  are  dependent,  but  a  uniting  energy  and  a 
unity  in  mind.  Fifty  million  molecules,  even  when  they  are  highly 
complex  and  unstable  phosporized  compounds,  gyrating  in  the  most 
wonderful  fashion  with  inconceivable  rapidity,  certainly  do  not 
constitute  07ie  thing.  They  do  not,  then,  by  molecular  constitution 
and  activities,  even  constitute  a  physical  basis  which  is  conceivable 
as  a  representative  or  correlate  of  one  thing.  Each  molecule  among 
them  all,  even  in  order  to  be  conceived  of  as  being  itself  one  such 
thing  among  the  other  millions  of  more  or  less  similar  but  not 
identical  molecules,  is  dependent  upon  this  same  synthetic  activity 
of  the  mind. 

§  9.  Still  further,  the  study  of  metaphysics  shows  us  that  certain 
assumptions,  which  are  not  of  a  sensuous  character,  or  verifiable 
at  all  by  an  appeal  to  the  sensations,  enter  into  every  presentation 
of  sense.  No  such  presentation  of  sense  consists  of  a  mere  put- 
ting together  of  individual  sensations.  Whatever  account  one  may 
choose  to  give  of  the  nature  and  origin  of  this  belief,  there  can  be 
no  doubt  that  all  men  do  believe  that  the  "  things  "  they  perceive 
are  neither  bare  groupings  of  mental  phenomena  nor  forms  of  the 
molecular  motion  of  a  nervous  mass  ;  men  believe  that  things  are 
real  existences  set  in  space  outside  of  their  OAvn  bodies.  Things 
are  known  as  real ;  they  are  supposed  to  Jtave  attributes  ;  they  act 
on  each  other  and  on  us  who  observe  them  ;  they  exercise  force  ; 
they  are  extended  and  movable  in  space,  and  continue  uninterrupt- 
edly through  more  or  less  of  time.  To  be  all  this  is  necessary  in 
order  to  be  a  "Thing."  Now,  the  assumptions  which  enter  into 
the  popular  belief  may  be  regarded  as  all  true  or  all  false,  or  as 
partly  false  and  partly  true,  in  the  form  in  which  men  ordinarily 
hold  them.  But  not  one  of  them  is  capable  of  being  justified,  or 
in  any  way  accounted  for,  by  an  enumeration  of  the  sensory  states 
into  which  consciousness  is  thrown  by  the  action  of  the  stimuli 
on  the  nervous  system.  Much  less  is  it  accounted  for  by  refer- 
ence to  certain  hypothetical  wave-like  motions  in  the  substance  of 
the  brain.  That  such  wave-like  motions  occur  we  have  no  doubt. 
That  the  changes  in  the  quantity  and  quality  of  the  sensations  are 
related  to,  and  dependent  upon,  the  intensity  and  the  kind  of  these 
motions  is  a  most  reasonable  conjecture.  That  the  motions  which 
are  correlated  with  the  presentations  of  sense  differ  in  kind  or  de- 


£96  MIND   AS    CONSCIOUS   BEING. 

gree  from  those  whicli  are  correlated  with  mere  images  of  imagi- 
nation may  also  be  true.  It  is  true,  furthermore,  that  our  percep- 
tions and  ideas  of  the  extension  and  motion  of  things  are  dependent 
for  their  characteristics  in  great  measure  upon  the  structure  of 
the  physical  organism.  But  it  is  impossible  to  conceive  of  any 
form  of  molecular  motion  which  could  serve  as  the  physical  basis 
or  physical  representative  of  any  of  those  metaphysical  assumptions 
which  enter  into  all  knowledge  of  things.  What  kind  of  nervous 
action  can  be  the  equivalent  of  an  unchanging  conviction  or  belief 
in  the  reality  and  true  causal  energy  of  all  things  both  visible  and 
invisible  ?  What  sjjlitting  up  of  the  chemical  constitution  of  the 
molecules  of  nervous  substance,  or  difference  in  the  character  of 
their  agitations,  can  be  conceived  of  as  analogous  to,  or  serving  as 
true  cause  of,  the  distinction  which  is  involved  in  our  speaking  of 
each  Thing  as  though  it  were  a  substance  with  attributes  ? 

Reference  to  Avhat  has  already  been  said  (Part  II.,  chapter  X.) 
concerning  the  impossibility  of  assigning  a  physical  basis  to  the 
mental  operations  of  voluntary  recollection,  with  its  recognition  of 
similarity,  to  attentive  choice,  and  to  all  the  discrimination  which 
underlies  the  work  of  the  intellect  proper,  will  furnish  further  oc- 
casion for  distinsting  the  above-mentioned  theory.  For  example, 
the  new  process  of  physical  excitation,  which  serves  as  the  "  basis  " 
—  so  to  speak — of  any  image  of  memory,  may  be  similar  to  the 
process  which  served  as  the  basis  of  the  original  presentation  of 
sense.  But  the  mental  act  of  recognizing  the  similarity  of  the  ob- 
ject before  the  mind  to  one  no  longer  before  it,  and  yet  of  distin- 
guishing the  former  from  the  latter  as  characterized  by  the  time  in 
which  it  occurs,  does  not  admit  of  being  conceived  of  under  any 
analogy  to  such  physical  processes.  The  same  thing  may  be  said 
of  consciousness  in  itself  considered,  and  so  of  every  mental  j)he- 
nomenon  considered  as  being  what  it  actually  is — a  phase  of  con- 
sciousness. But  to  make  clear  this  aspect  of  the  case  requires  that 
we  should  resume  the  consideration  of  the  so-called  "material- 
istic" theory  of  the  relations  between  mental  j^henomena  and  ner- 
vous substance  from  a  slightly  different  point  of  view. 

§  10.  There  can  be  no  doubt  that  the  popular  and  wellnigh  imi- 
versal  belief  regards  the  subject  of  the  mental  phenomena  as  a  real, 
non-material,  and  permanent  being.  This  belief  also  undoubtedly 
regards  this  subject  as  on«  indivisible  being,  a  "unit-being."  In 
other  words,  the  prevalent  conception  of  the  Mind  is  that  of  an 
existence  which  is  spiritual  and  is  a  unity  in  some  unique  sense. 
The  many  objections  which  have  been  raised  against  the  belief 
may  be  divided  into   two  classes — one  of  which  may  be   called 


IKFLUENCE   OF   THE   BLOOD-SUPPLY.  597 

metaphysical,  and  the  other  physiological  or  physical.  The  meta- 
physical objections  arise,  in  part,  from  the  difficulty  which  is  felt 
in  defining  what  is  meant  by  "  reality,"  "  spirituaUty  "  (or  non- 
materiality),  and  "  unity  "  in  that  strict  sense  in  which  these  terms 
are  thought  to  apply  to  the  mind.  The  consideration,  both  of 
these  objections  and  of  that  way  of  considering  the  facts  which  es- 
capes them  as  far  as  possible,  will  be  for  the  present  postponed. 
But  the  other  class  of  objections  arises  from  the  very  facts  with 
which  it  is  the  special  business  of  the  science  of  Physiological 
Psychology  to  deal.  It  may  be  summarily  stated  in  the  form  of 
questions  like  the  following  :  What  kind  of  permanent  reality  can 
belong  to  a  being  whose  essential  characteristic  of  having  various 
states  of  consciousness  can  be  temporarily  laid  aside  when  the  brain 
sleeps  or  is  deprived  of  its  blood-supply ;  or  can  be  wholly  lost 
when  certain  nervous  centres  are  subjected  to  permanent  pressure 
or  destroyed  by  disease  or  the  surgeon's  knife  ?  How  can  non- 
materiality  be  affirmed  of  phenomena  which — so  far  as  we  can 
trace  them  at  all — exist  only  in  immediate  dependence  upon  a  cer- 
tain chemical  constitution,  structural  form  and  arrangement,  and 
functional  activity  of  material  atoms  ?  How  can  the  claim  of  be- 
ing the  highest  unity  be  made  for  that  which  exists  at  all  only  as  it 
is  in  a  constant  flux  ;  which,  indeed,  is  possessed  of  its  one  charac- 
teristic activity  of  being  conscious,  only  on  condition  that  it  divides 
itself  into  subject  and  object  and  experiences  a  constant  change  of 
the  f oi'ms  in  which  it  is  conscious  ? 

In  spite  of  such  objections  from  the  physiological  point  of  view 
as  are  the  foregoing,  the  popular  assumption,  when  freed  from  its 
crudities  and  interpreted  intelligently,  may  be  shown  to  be  the  only 
one  compatible  with  all  the  facts  of  obsei'vation.  It  may  be  shown 
that  it  is  demanded  by  these  facts.  On  the  contrary,  the  attrib- 
uting of  mental  phenomena  to  the  substance  of  the  brain  (with  or 
without  including  the  rest  of  the  nervous  substance)  does  not  satisfy 
the  facts  of  observation.  The  relation  between  brain  and  mind  is 
not  such  that  the  former  can  be  considered  as  a  real  being,  of  which 
the  phenomena  of  the  latter  may  be  regarded  as  activities.  Another 
real  being  must  be  assumed  to  exist  as  the  subject  of  the  mental 
phenomena — a  being  with  a  nature  quite  unlike  that  of  material 
molecules. 

§  11.  The  phenomena  whose  relation  to  the  molecules  of  the  ner- 
vous system  is  in  dispute  are  phenomena  of  consciousness.  Noth- 
ing in  regard  to  these  phenomena  is  more  impressive,  upon  first 
subjecting  them,  as  such,  to  introspective  observation,  than  their 
surprising  complexity  in  unity.     Or  we  may  rather  say,  the  way  in 


598  MIISTD   AS   CO]SrSCIOUS   BEING. 

A,\-lnch  all  states  of  consciousness,  however  different  they  may  be 
with  respect  to  characteristic  quality  or  origin,  are  attributed  by 
the  conscious  subject  to  one  subject  as  his  own  states  is  the  most 
surprising  of  all  facts.  This  fact  underlies  all  the  truths  and  law? 
into  which  psychology  inquires,  whether  starting  from  the  physio- 
logical or  from  some  other  point  of  view. 

It  has  been  customary  for  psychologists  to  classify  all  the  mental 
phenomena  under  a  few  so-called  "  faculties  "  of  the  mind.  The 
objection  has  often  been  made  to  such  classification  that  it  tends 
to  confuse  or  destroy  a  just  appreciation  of  the  unity  of  mind.  A 
more  obvious  objection  to  the  ordinary  psychological  classification 
is  perhaps  this,  that  it  fails  to  take  due  account  of  the  vast  com- 
plexity of  mental  phenomena.  For — it  should  never  be  forgotten — 
mental  phenomena  are  always,  primaribj  considered,  nothing  more 
than  events.  This  is  true  of  sensations  and  perceptions,  with  all 
their  objective  reference,  as  well  as  of  acts  of  imagination  and  of 
so-called  pure  thought.  The  yellow  of  the  watch,  the  red  of  the 
rose,  which  I  see,  are  modes  of  the  affection  of  my  consciousness. 
Excluding  for  the  present  all  reference  to  any  metaphysical  assump- 
tions, these  colors  are  simply  events  in  consciousness.  The  real 
jDrocesses  outside  of  consciousness — the  objective  existences  and 
events — to  which  the  events  in  consciousness  are  referred  by  science 
are  in  no  sense  similar  to  the  events  of  consciousness  themselves. 
What  the  real  process  outside  of  consciousness  is — whether  it 
consist  of  I'apidly  vibrating  waves  of  ether,  or  of  photo-chemical 
changes  in  the  tissues  of  the  retina,  or  of  nerve-commotions  prop- 
agated along  the  optic  nei've  and  in  the  upper  occipital  lobe  of 
the  brain — we  know  only  by  doubtful  inference  from  certain  con- 
scious affections  of  our  own  to  certain  material  existences  assumed 
to  exist  out  of  consciousness.  Whether  the  right  to  make  these 
inferences  be  disputed  or  allowed,  there  can  be  no  dispute  over  the 
statement  that  the  phenomena  of  conscious  vision  are  not  copies  of 
any  of  these  external  events.  What  is  tnie  of  colors  is  also  plainly 
true  of  smells,  and  tastes,  and  sounds.  These  sensations  are  all 
events  in  consciousness.  Recent  researches  into  the  nature  of  the 
sensations  which  come  through  the  excitation  of  the  skin  show  that 
these  also  are,  primarily  considered,  mental  events  of  various  kinds  ; 
such  as  having  the  feeling  of  cold,  or  of  heat,  or  of  pain,  or  of 
pressure,  or  of  motion,  etc. 

Moreover,  the  modern  experimental  view  of  the  way  in  which  the 
sensations  are  localized  and  synthetically  combined  to  form  the 
presentations  of  sense  shows  that  the  latter  also  must  be  consid- 
ered as  being,  primarily,  mental  events.     Of  course  there  is  a  sense 


COMPLEXITY   OF   MENTAL   PHElSTOMElSrA.  599 

in  which  it  is  absurd  to  say,  not  simply,  "Perceptions  of  things  are 
always  merely  mental  events  ; "  but  also,  "  Things  themselves  are 
merely  mental  events."  It  has  already  been  shown  that  certain  as- 
sumptions enter  into  all  our  perceptions  and  conceptions  of  so- 
called  "  things  ;  "  but  that  even  the  attempt  to  account  for  these 
assumptions,  by  assigning  them  to  any  conceivable  form  of  a  physi- 
cal basis  in  the  brain,  leads  to  absurdity.  Still  there  is  also  a  sense 
in  which  "  things,"  that  can  certainly  never  be  any  different  with 
respect  to  their  known  qualities  from  the  way  in  which  they  appear 
to  us  when  perceived,  are  mental  events.  Sensations  are  mental 
events  ;  the  discriminating,  combining,  and  localizing  of  sensations 
are  mental  events.  Things  to  us  are  never  more  than  discrimi- 
nated, combined,  and  localized  sensations,  p?i<s  the  metaphysical 
assumptions  to  which  reference  has  been  made. 

§  12.  Eeflection  upon  facts  like  those  just  stated  leads  us  to  won- 
der at  the  enormous  complexity  of  mental  phenomena.  For  the 
purposes  of  the  jji'^ctical  life  we  are  warranted  in  regarding  the 
surrounding  world  as  composed  of  a  limited  number  of  material 
existences  that  undergo  little  or  no  change  from  day  to  day.  But 
this  way  of  regarding  the  objects  of  experience  does  not  at  all 
satisfy  the  demands  of  psychological  inquiry.  Such  inquiry  con- 
siders the  knowledge  of  external  nature,  as  well  as  of  what  is  recog- 
nized as  pertaining  most  strictly  to  the  world  within,  to  involve  an 
unceasing  change  in  the  activities  of  consciousness.  Indeed,  with 
the  limitations  already  referred  to,  we  may  say  that  the  entire 
world,  so  far  as  it  is  our  world,  consists  only  of  these  changing 
states.  It  follows,  then,  that  the  first  truth  of  which  we  have  to 
take  account  is  the  following :  Our  entire  conscious  existence — 
whether  regarded  simply  as  being  ourselves  affected  in  a  certain 
way  or  as  having  a  purely  objective  experience  of  the  existence  and 
qualities  of  so-called  Things — is  a  continually  shifting  succession 
of  individual  mental  activities,  no  one  of  which  is  exactly  like  any 
other  or  is  to  be  considered  as  a  mere  repetition  of  any  other. 

It  would  be  acknowledged  by  all  that  a  mental  state  of  pain  on 
account  of  toothache  is  different  from  a  state  of  pleasure  in  smell- 
ing a  rose  ;  that  the  sensation  of  yellow  is  vinlike  the  sensation  of 
i-ed,  and  that  these  sensations,  in  common  with  all  sensations  of 
color,  are  unUke  those  of  touching  a  cold  piece  of  iron  or  of  hear- 
ing a  musical  tone.  All  the  practical  activities  of  men  are  based 
upon  the  conviction  that  the  individual  things  with  which  they 
deal  differ  from  each  other — not  simply  in  respect  to  the  qualities 
they  have,  and  the  degree  in  which  they  severally  possess  these 
qualities,  but  also  as  separate  real  beings  differ.     But  the  tinith 


600  MIND   AS    CONSCIOUS   BEING. 

now  undei'  consideration  reaches  further  than  this  common  ac» 
knowledgment.  Strictl}'  speaking,  from  the  point  of  view  taken  by 
an  analysis  of  consciousness,  the  same  so-called  "  thing  "  is  never 
in  experience  twice  the  same.  Every  time  that  it  exists  before  the 
mind,  as  a  presentation  of  sense,  it  is  constituted  anew  by  an  ac- 
tivity of  the  mind.  Unless  various  localized  sensations  and  re- 
membered images  of  sensations  are  "synthesized "under  the  laws 
which  govern  such  kinds  of  mental  phenomena,  there  can  be  no 
presentation  of  sense  ;  and  the  only  "  thing  "  which  has  immedi- 
ate existence  for  us  is  the  presentation  of  sense.  Accordingly,  the 
variety  of  the  mental  phenomena,  when  we  begin  the  attempt  to 
classify  them,  appears  as  great  as  that  of  all  the  individual  acts 
and  states  of  consciousness,  whether  those  acts  and  states  have 
reference  to  comparatively  unchanging  beings  outside  of  conscious- 
ness or  not. 

Even  a  description  of  the  different  kinds  of  mental  phenomena 
which  psychological  science  proposes  to  explain  would  be  impos- 
sible, if  the  foregoing  truth  were  not  merely  one  side  of  the  whole 
truth.  For  what  is  infinite  in  variety  and  always  changing  its  kind 
cannot  be  described.  There  could  then  be  no  science  of  the  mental 
phenomena,  no  classification  of  the  states  of  consciousness,  or  ex- 
planation of  them  by  relating  them  to  each  other  and  to  the  physical 
basis  on  which  they  are  supposed  to  rest. 

§  13.  Observation  of  the  jjhenomeua  of  consciousness,  liowever, 
shows  us  that  they  are  plainly  classifiable,  and  that  the  authority  on 
which  this  classifying  reposes  is  immediate  and  indisputable.  For 
the  phenomena  of  consciousness  ai'e  directly  recognized  in  con- 
sciousness as  like  or  unlike  with  varying  degrees  of  similarity  and 
dissimilarity.  They  are  assigned  by  everyone  possessed  of  a  de- 
veloped experience  to  this  or  that  class,  without  any  question  that 
the  act  of  classification  is  legitimate  and  correct.  The  number  of 
distinguishable  colors,  or  kinds  of  visual  sensations,  is  indeed  in- 
definitely large  ;  and  so  is  the  number  of  sensations  of  musical 
tone.  The  power  to  raake  all  the  necessary  discriminations  in  these 
sensations  varies  greatly  with  different  persons.  It  is  perfectly 
proper  to  say  that  the  number  of  kinds  of  the  states  of  conscious- 
ness arising  through  the  senses  of  sight  and  sound  varies  greatly 
in  different  individuals.  There  are  many  more  colors  and  tones 
for  some  men  than  for  others.  The  qualities  belonging  to  the  sen- 
sations wbich  follow  excitation  of  the  skin  are  also  diverse  ;  and, 
in  the  case  of  sensations  of  smell,  the  means  of  classification  for 
each  individual  are  limited  chiefly  by  the  number  of  the  different 
smellable  things  with  which  he  has  happened  to  come  in  contact. 


DIFFEEENCES   IN   PHET^OMENA.  601 

It  must  also  be  confessed  that  the  j)opular  classifications  of  the 
states  of  consciousness,  as  based  on  conscious  experience  itself,  is 
not  infrequently  erroneous.  So  far  as  the  sensations  are  concerned, 
this  is  partly  due  to  the  fact  that  they  are  ordinarily  referred  to  some 
thing  or  to  some  part  of  the  body,  which  is  only  approximately  cor- 
rect, and  yet  correct  enough  for  practical  purposes.  The  taste  of 
the  onion  is  no  less  clearly  distinguished  from  other  states  of  sensa- 
tion arising  through  the  mouth  because  the  subject  of  the  taste  does 
not  know  that  his  sensations  are  in  fact  largely  sensations  of  smell. 
Because  one  believes  that  one  tastes  the  pepper  instead  oi  feels  it 
with  the  tongue,  one  has  lost  none  of  one's  power  to  make  clear  dis- 
criminations in  the  domain  of  consciousness.  Nor  is  this  power 
taken  from  the  color-blind,  although  the  length  of  their  color-spec- 
trum is  shortened  so  that  they  have  a  less  extended  domain  of  sen- 
sations of  this  order  within  which  to  discriminate. 

It  appears,  then,  that  likenesses  and  unlikenesses  in  the  phe- 
nomena of  consciousness,  and  an  immediate  "awareness" — so  to 
speak — of  these  likenesses  and  unlikenesses,  or  direct  discrimina- 
tion by  consciousness  of  the  quality  of  the  states  of  consciousness,  as 
such,  are  involved  in  that  classification  of  the  mental  phenomena 
which  all  men  make.  If  the  classification  becomes  more  refined 
and  elaborate,  it  at  no  time  ceases  to  repose  on  the  same  founda- 
tion. All  classifications  of  mental  phenomena  which  have  any  other 
foundation,  or  which  introduce  any  other  consideration  than  the 
simple  one  of  how  I,  the  conscious  subject,  am  affected,  are  not 
really  classifications  of  mental  phenomena  as  such.  Such  alleged 
classifications  may  indeed  tell  us  much  that  scientific  inquiry  de- 
sires to  know  about  the  origin  or  correlations  of  the  mental  phe- 
nomena. They  may  assume  to  say  what  special  part  of  the  external 
organ  of  sense,  or  what  special  area  of  the  brain,  is  more  direct- 
ly concerned  in  producing  the  physical  state  which  precedes  or 
causes  the  mental  phenomena.  They  may  demonstrate  what  kind 
of  physical  stimuli  result,  respectively,  in  exciting  such  and  such 
states  of  consciousness.  But  they  tell  nothing  whatever  as  to  what 
the  phenomena  really  are,  whether  like  or  unlike,  or  as  to  how  they 
may  be  ranged  and  rated  together.  They  are  classifications  of  the 
causes,  or  occasions,  or  physical  excitements  of  the  mental  phe- 
nomena ;  they  are  not  classifications  of  mental  phenomena,  as  such. 

§  l-i.  Moreover,  the  principles  which  regulate  the  formation  of 
classes  among  the  conscious  states  of  the  mind  are  very  different 
from  those  which  regulate  the  proposal  to  classify  the  elements  of 
the  physical  basis  of  these  states,  or  the  molecular  activities  of 
these  elements.     To  be  sure,  the  Youug-Helmholtz  theoiy  of  vis- 


602  MI]S"D   AS   CONSCIOUS   BEING. 

ual  sensations  proposes  to  distinguisli  red,  green,  and  yellow  as 
the  three  kinds  of  retinal  elements  ;  and  the  opto-ehemical  theory 
of  vision  speculates  as  to  the  classes  of  pigments  connected  with 
the  seeing  of  various  colors.  It  has  bee^  held  by  some  physiolo- 
gists that  the  two  main  parts  of  the  inner  ear  (vestibule  and  coch- 
lea) correspond  to  the  two  principal  classes  of  sensations  of  sound 
(to  noises  and  musical  tones) ;  or  even  that  the  vibration  of  an  in- 
dividual nervous  element  in  the  organ  of  Corti  represents,  in  some 
sort,  each  definite  one  among  the  many  states  of  consciousness  that 
constitute  our  hearing  of  a  melody.  Sensations  of  feeling  may  be 
classified  as  of  peripheral  or  central  origin,  in  reference  to  the 
place  from  which  the  nervous  impulses  occasioning  them  are  sup- 
posed to  take  their  rise.  But  one  need  not  be  deceived  by  all  this. 
The  "  red  "  retinal  elements  are  not  themselves  red  ;  and  if  they 
did  appear  of  this  color  to  external  observation,  it  would  not  in  the 
least  degree  help  us  the  better  to  understand  what  is  the  quality 
of  that  state  of  consciousness  which  we  call  the  sensation  of  red. 
The  different  nervous  elements  of  the  organ  of  Corti  may  be  capa- 
ble of  being  aiTanged  in  a  scale  ;  if  so,  they  are  classified  as  longer 
or  shorter,  and  as  arranged  in  space  one  above  the  other.  But  this 
classification  is  in  no  real  respect  like  that  which  we  make  when  we 
arrange  the  states  of  consciousness  called  musical  tones  in  a  scale 
of  their  pitch. 

In  general,  the  physical  elements  of  the  nervous  system  are  di- 
visible into  classes  according  to  their  chemical  constitution — as, 
for  example,  the  phosphorized  and  the  non-phosphorized  proximate 
principles  of  the  brain  ;  or,  according  to  their  structural  form,  into 
nerve-fibres  and  nerve-cells  of  a  great  variety  of  shapes,  sizes,  etc.  ; 
or,  according  to  their  physiological  function,  into  afferent  and  effer- 
ent, reflex  or  inhibitory  or  automatic.  But  no  such  principles  of 
division  can  be  carried  over  to  the  mental  phenomena.  They  have 
absolutely  no  applicability  to  these  phenomena,  as  such.  We  cannot 
introduce  distinctions  of  chemical  constitution,  structural  form,  and 
physiological  function  into  sensations  and  ideas,  into  feelings  and 
thoughts  and  acts  of  will.  A  phosphorized  thought,  or  a  stellate 
feeling,  or  an  afferent  thought,  are  phrases  that  have  no  meaning. 

Nor  should  we  be  any  better  able  to  apply  the  jDrinciples  by  which 
we  classify  the  different  factors  of  the  physical  basis  of  conscious- 
ness to  the  phenomena  of  consciousness  itself,  in  case  we  had  a 
much  more  minute  acquaintance  with  those  factors.  Let  it  be  sup- 
posed that  psycho-physical  science  should  so  far  advance  as  to  be 
able  to  tell  precisely  what  kinds  of  molecular  activities  of  what 
nervous   elements  are  correlated  with  all  the  various  classes  of 


PRINCIPLES   OF   CLASSIFICATION.  603 

mental  plienomena.  The  latter  woiild  still  remain  precisely  such 
as  they  are  in  kind ;  they  would  still  have  to  be  classified,  if  at  all, 
on  the  ground  of  their  hkenesses  and  unlikenesses  as  directly 
known  in  consciousness.  If  it  should  be  discovered  that  the  mo- 
lecular agitation  of  a  particular  group  of  fibres  and  cells  in  the  or- 
gan of  Corti  is  necessary  in  order  to  produce  the  sensation  of  the 
musical  note  a  ,  and  that  this  agitation  resembles  that  which  some- 
what similar  fibres  and  cells  in  the  retina  undergo  preceding  the 
sensation  of  a  particular  shade  of  green,  the  two  sensations  would 
then  be  no  easier  to  classify  together  than  they  are  now.  Both 
stand  near  the  middle  of  their  respective  scales.  In  that  respect 
it  might  be  said  that  the  sensation  of  the  musical  tone  a  is  like  the 
sensation  of  green.  This  point  of  likeness  is  really,  however,  one 
that  appertains  solely  to  a  physical  quality  or  function  in  certain 
bits  of  nervous  matter  more  or  less  directly  connected  with  the 
physical  antecedents  of  the  sensations  ;  it  cannot  be  conceived  of 
as  appertaining  to  the  sensations  themselves. 

§  15.  Considerations  derived  from  the  theory  of  the  quantity  of 
stimuli  and  their  resulting  intensities  in  the  states  of  conscious- 
ness might  be  urged  in  the  same  direction.  The  variations  in  the 
amount  of  the  molecular  processes  within  the  nervous  system  are 
all  measurable  and  classifiable,  if  at  all,  on  principles  with  which 
physics  is  familiar.  The  excitation  in  the  nervous  system  always 
consists  simply  of  so  many  molecules,  having  such  a  chemical  con- 
stitution, moving  so  much  in  such  a  direction  with  relation  to  each 
other.  But  the  most  nearly  related  mental  phenomena  are  feelings, 
and  judgments  comparing  feelings,  such  as  can  be  expressed  only 
somewhat  as  follows  :  "  Now  that  shade  of  red  seems  to  me  a  little 
more  intense  ;"  or,  "now  I  think  something  has  been  added  to  the 
sensation  of  pressure ; "  or,  "  I  should  call  this  note  the  major 
third  of  the  other."  In  general,  we  may  say  that,  quantitatively 
considered,  the  changes  in  the  nervous  mechanism  are  all  precisely 
alike  as  to  kind — that  is,  are  all  that  mode  of  motion  called  "nerve- 
commotion  " — and  admit  of  being  measured  off  by  a  common  phys- 
ical standard  or  unit  of  measure.  But  the  mental  phenomena  are 
classifiable  only  as  a  succession  of  states,  that  are  continually  chang- 
ing their  qualit}'  and  have  no  quantitative  measure  which  we  can 
separate  from  these  changes  of  quality.  Nerve-commotions  can  be 
conceived  of  as  added  and  subtracted,  switched  to  the  right  or  to 
the  left,  concentrated,  distributed,  dissipated.  But,  strictly  speak- 
ing, the  resulting  mental  phenomena  admit  of  no  treatment  of  this 
sort.  Every  sensation  exists,  if  at  all,  as  an  indivisible  qualitative 
state  of  consciousness  ;  it  cannot  even,  as,  such  state,  be  retained  to 


604  MIND    AS    CONSCIOUS   BEING. 

be  compared  with  some  other  succeeding  state,  in  order  to  decide 
whether  it  is  more  or  is  less  in  respect  to  quantity.  Without 
memory  and  comparison,  which  are  complex  activities  of  mind  dif- 
ferent from  the  mere  having  of  sensation,  we  could  not  affirm  of 
any  mental  state  that  it  is  more  or  less  than  another. 

Still  further,  other  forms  of  mental  activity  which  have  an  un- 
doubted reality  do  not  admit  of  even  the  loose  application  to  them 
of  terms  of  quantity  which  is  proper  when  speaking  of  sensations 
and  feelings.  A  "  weighty"  judgment  and  a  "  high  "  ideal  ai'e  not 
to  be  measured  by  standards  that  admit'  of  correlation  with  the  in- 
creasing or  diminishing  swing  of  nervous  molecules.  Yet  if  those 
classes  of  the  phenomena  of  consciousness  which  these  words  imply 
have,  as  such,  any  physical  basis  whatever,  this  basis  must  consist 
in  some  form  of  nerve-commotion  as  to  the  quantity  of  which  an 
exact  measurement  is  conceivable.  If,  however,  a  wide  swing  of 
the  molecules  were  found  to  go  with  a  good,  sound,  clear  judg- 
ment, and  a  contracted  swing  to  be  the  physical  cause  of  narrow- 
ness of  mental  apprehension,  such  a  fact  would  not  help  us  in  any 
regard  the  better  to  revise  the  Aristotelian  classification  of  the  syl- 
logism. Reasoning,  as  a  mental  activity,  would  be  deductive  or 
inductive,  analytic  or  synthetic,  as  before,  after  making  the  discov- 
ery that  the  one  process  is  connected  with  a  continual  diminution 
of  the  cortical  areas  over  which  the  nerve-commotions  spread  them- 
selves, and  the  other  with  a  noble  diffusion  of  such  commotions 
over  an  ever-widening  expanse  of  the  brain. 

§  16.  It  is  an  undoubted  fact,  however,  that  mental  phenomena 
admit  of  a  fairly  satisfactory  arrangement  into  classes.  The  ar- 
rangement can  be  made  only  upon  the  basis  of  their  likenesses  and 
unlikenesses  as  known  in  consciousness  and  by  consciousness.  No 
other  arrangement  of  these  phenomena,  as  such,  is  possible — none 
that  is  not  founded  upon  the  same  ultimate  facts  thus  distinguished. 
All  attempts  at  an  arrangement  of  them  by  other  principles,  and 
from  other  points  of  view,  result  in  the  classification  of  something 
else  (such  as  the  physical  antecedents,  causes,  or  concomitants) 
than  the  phenomena  themselves.  It  is  not  strange,  then,  that  the 
"old  psychology"  won  its  principal  triumphs,  by  the  method  of 
introspection,  within  the  field  of  classification.  The  crude  begin- 
nings of  a  physiological  psychology  in  the  phrenology  of  Gall  and 
Spurzheim  were  obliged  at  that  time  to  accept  from  introspective 
psychology  its  division  of  the  mind's  activities  into  so-called  "  fac- 
ulties." In  its  more  scientific  and  experimental  form  at  the  pres- 
ent time  physiological  psychology  is  just  as  dependent  as  ever 
upon  introspective  psychology  for  a  classification  of  the  mental 


KINDS    OF   MENTAL    PHENOMElSrA.  605 

phenomena.  The  inti'ospective  science  of  mind  has  already  arrived 
at  very  general  agreement  upon  this  point. 

It  is  very  generally  agreed  that  all  the  mental  phenomena  are 
classifiable  under  three  great  heads — into  phenomena  of  knowing, 
phenomena  of  feeling,  and  j^henomena  called  acts  of  will.  The 
distinction  of  the  two  latter  classes  of  phenomena  is,  indeed,  a  mat- 
ter established  in  comparatively  recent  times.  A  certain  number 
of  investigators,  who  use  the  method  of  introspection,  still  venture 
to  affirm  that  acts  of  feeling  in  the  form  of  desire  are  not  to  be  dis  ■ 
tinguished  as  differing  in  kind  from  acts  of  will.  In  their  view, 
so-called  acts  of  will  are  resolvable  into  phenomena  of  feeling. 
But  the  oiDinion  of  the  great  majority  of  students  of  psychology 
is  decidedly  in  favor  of  adhering  to  the  threefold  division  of  the 
mental  faculties.  There  is  also  a  large  amount  of  agreement  as  to 
the  sub-classes  that  fall  under  these  three — at'  any  rate,  with  the 
exception  of  the  varied  efforts  made  to  deal  with  the  very  complex 
phenomena  of  feeling  in  its  many  forms.  The  more  recent  at- 
tempts (made  especially  by  certain  English  writers  on  psychology) 
to  depart  from  the  accepted  classifications  of  the  "  old  psychology" 
have  attained  little  or  no  valuable  result.  These  attempts  have  in- 
troduced into  psychology  a  great  number  of  uncouth  terms,  derived 
largely  from  false  analogies  of  physical  science,  which  tend  to  rep- 
resent the  case  as  though  sensations  could  be  weighed  or  measured 
or  compounded  like  the  nervous  shocks  which  cause  them,  and  as 
though  ideas  could  become  "  agglutinated  "  or  "agglomerated" 
like  globules  of  mercury  or  minute  particles  of  water.  Such  at- 
tempts, however,  have  thrown  no  light  on  the  nature  of  the  mental 
phenomena,  or  on  the  question  of  their  correct  classification  ;  they 
have  not  really  succeeded  in  supplanting  or  discrediting  the  classi- 
fications of  the  "  old  psychology."  Nor  is  it  at  all  likely  that  the 
principal  classes  into  which  all  mental  phenomena  are  now  throvni 
will  ever  be  changed.  The  "faculties"  of  the  mind — however  the 
term  is  to  be  understood — will  remain  the  same.  At  all  events,  if  a 
change  should  be  made  in  these  divisions,  such  change  could  only 
be  accomplished  by  the  method  of  introspection. 

§  17.  The  question  may  now  be  raised  :  How  are  we  to  account 
for  facts  like  the  foregoing  ?  In  attempting  an  answer  to  this 
question,  the  great  significance  of  the  facts  themselves  should  be 
recalled.  It  has  been  shown  that  mental  phenomena  cannot  be 
conceived  of  as  identical  with  the  molecular  motions  of  the  nervous 
mass  ;  and  that  the  fundamental  relations  between  the  two  cannot 
be  expressed  by  the  statement,  the  phenomena  of  consciousness  are 
the pr-oduct,  of  the  brain — in  any  meaning  of  the  word  "product" 


606  MIND   AS   CONSCIOUS   BEING. 

wliicb  can  be  clearly  defined.  Nor  can  tbe  tlieory  be  accepted  that 
every  mental  state  and  process  bas  its  exact  equivalent,  with  respect 
to  all  its  factors,  in  some  antecedent  or  concomitant  state  or  pro- 
cess of  cerebral  nerve-fibres  and  nerve-cells,  and  that  therefore  all 
mental  phenomena  are  to  be  directly  and  exclusively  referred  to 
these  physical  structures  as  their  sole  subject  or  ground.  More- 
over, it  has  been  found  necessary  to  admit  that  mental  phenomena, 
as  such,  can  be  classified  only  by  introspection  ;  and  that  the  prin- 
ciples on  which  the  classification  must  be  based  differ  from  those 
applicable  to  the  nervous  substance,  while  the  actual  classes  discov- 
ered by  the  only  available  method  do  not  correspond  to  any  of 
those  with  which  physics  and  physiology  make  us  familiar.  And 
yet  there  is  no  insuperable  difficulty  in  classifying  the  phenomena 
of  mind.  Introspective  psychology  furnishes  us  with  a  classifica- 
tion, on  the  whole,  tolerably  satisfactory 

What,  then,  is  the  fair  inference  from  all  these  facts  with  respect 
to  a  decision  between  the  two  theories  of  mind  which  were  previ- 
ously proposed  ?  (See  §  3. )  Plainly,  such  inference  favors  looking 
toward  some  other  subject  or  ground  of  the  mental  phenomena 
than  the  nervous  substance  of  the  brain.  Its  result  commends  sub- 
stantially the  same  view  as  that  held  by  the  great  majority  of  man- 
kind. We  shall  state  and  explain  this  view,  however,  in  different 
terms  from  those  employed  by  this  majority. 

The  phenomena  of  human  consciousness  miud  he  regarded  as  activi- 
ties of  some  other  form  of  Beat  Being  than  the  moving  molecules  of 
the  brain.  They  require  a  subject  or  ground  which  is  in  nature 
unlike  the  phosjDhorized  fats  of  the  central  masses,  the  aggregated 
nerve-fibres  and  nerve-cells  of  the  cerebral  cortex.  This  real  be- 
ing, thus  manifested  immediately  to  itself  in  the  phenomena  of 
consciousness,  and  indirectly  to  others  through  the  bodily  changes, 
is  the  Mind.  To  it  the  mental  phenomena  are  to  be  attributed  as 
showing  what  it  is  by  what  it  does.  The  so-called  mental  "  fac- 
ulties "  are  only  the  modes  of  the  behavior  in  consciousness  of  this 
real  being.  We  actually  find,  by  the  only  method  available,  that 
this  real  being  called  Mind  behaves  in  certain  perpetually  recur- 
ring modes  ;  therefore,  we  attribute  to  it  certain  faculties.  The 
mental  faculties,  then,  are  not  entities  that  have  an  existence  of 
themselves  ;  nor  are  the  individual  behavings  of  the  mind  (the 
so-called  "  ideas  ")  existences  that  can  become  "  agglutinated  " 
or  "  associated  "  or  "  compounded  "  in  any  way.  They  are  not 
divisions  of  the  mind  ;  nor  are  they  powers  of  the  mind,  if  by 
this  word  be  meant  some  permanent  recognizable  reality,  stored 
up  in  a  s^Diritual  subject,  or  attached  to  it  or  inherent  in  it,  after 


'     THE   UNITY   OF   CONSCIOUSNESS.  607  . 

the  analogy  of  tlie  relation  of  physical  forces  to  their  subjects,  the 
atoms.  The  faculties  of  the  mind  are  the  modes  of  the  behavior, 
in  consciousness,  of  the  mind.  And  the  very  nature  of  the  classi- 
fying acts  "which  lead  to  their  being  distinguished  is  explicable 
only  upon  the  assumption  that  a  real  being  called  mind  exists,  and 
is  to  be  distinguished  from  the  real  beings  known  as  the  physical 
molecules  of  the  brain's  nervous  mass. 

That  the  subject  of  the  states  of  consciousness  is  a  real  being, 
standing  in  certain  relations  to  the  material  beings  which  com- 
pose the  substance  of  the  brain,  is  a  conclusion  warranted  by  all 
the  facts.  That  the  modes  of  its  activity  in  consciousness  are  cor- 
related under  law  with  the  activities  of  the  brain-substance  is  a 
statement  which  Physiological  Psychology  confirms ;  one  upon 
which,  indeed,  it  is  largely  based.  It  will  be  our  task,  in  a  subse- 
quent chapter,  to  consider  under  what  general  terms  such  correla- 
tion may  best  be  expressed.  All  physical  science,  however,  is  based 
upon  the  assumption  that  real  beings  may  have  an  existence  such 
as  is  sometimes  called  "  independent,"  and  yet  be  constantly  re- 
lated to  each  other  under  known  or  discoverable  laws.  If  this  as- 
sumption could  not  be  made  and  verified,  all  the  modern  atomic 
theory  would  stand  for  nothing  but  a  vain  show  of  abstractions. 
Upon  what  grounds  of  reason  or  courtesy — we  may  inquire  at  this 
point — does  Materialism  decline  to  admit  the  validity  of  similar  as- 
sumptions as  demanded  by  mental  phenomena  ? 

§  18.  The  foregoing  view  of  the  mind  and  its  faculties  is  greatly 
confirmed  by  a,nother  consideration.  Consciousness  has  a  certain 
remarkable  unity.  If  the  complexity  of  mental  phenomena  is  be- 
wilderingly  great,  the  unity  of  consciousness  is  striking  and  unique. 
Many  disputed  questions  may  be  raised  touching  the  essential  nat- 
ure of  this  unity,  the  means  we  have  for  recognition  of  it,  and  the 
inferences  which  may  legitimately  be  drawn  therefrom.  Some  of 
these  questions  will  be  merely  alluded  to  at  this  point,  and  their 
further  consideration  postponed  until  later  on. 

All  developed  forms  of  consciousness  involve  an  attribution  of  the 
present  particular  state  of  consciousness  to  a  subject  of  the  state. 
It  is  for  this  reason,  as  has  already  been  remarked,  that  we  express 
each  state  of  our  consciousness  by  saying  :  "/am  in  such  or  such 
a  condition  ;  "  "/feel  thus  and  so  ;"  "/  see,  or  hear,  or  smell,  or 
taste,  or  think,  or  plan,"  etc.  Such  language — and  all  language  de- 
signed to  describe  our  mental  phenomena  is  such — plainly  shows 
that  some  kind  of  distinction  is  made  by  everyone  between  the 
state  and  the  "^gfo"  which  is  the  subject  of  the  state.  It  is  no 
adequate  explanation  of  this  fact  to  say  that  by  the  subject,  in  all 


608  MIND    AS    CONSCIOUS    BEING. 

these  sentences  (the  "I"  to  which  the  states  are  attributed),  we 
mean  to  denote  a  mere  concept  of  myself  formed  upon  the  basis 
of  past  experience.  Such  a  concept  may  indeed  be  formed.  Its 
completeness  and  correctness  furnishes  an  excellent  test  of  the 
amount  of  development  attained  by  each  individual  in  self-knowl- 
edge. Few  individuals,  however,  would  be  found  able  to  give  a 
statement,  at  all  satisfactory  to  themselves  or  to  others,  of  just  what 
characteristics  are  to  be  considered  peculiar  to  their  "self -hood." 
"We  do  not,  then,  merely  designate  the  "self"  when  we  thus  con- 
stantly refer  to  the  "  I "  which  is  the  subject  of  each  state.  Our 
knowledge  that  the  state  is  our  state,  or  that  we  are  in  this  definite 
individual  state,  is  perfectly  clear  and  immediately  conclusive  with 
reference  to  all  the  experience  we  have  or  can  remember. 

The  clearness  and  immediateness  of  the  reference  which  we  are 
continually  making  of  our  states  to  the  subject  of  them  all  is  in 
marked  contrast  with  the  obscurity  and  indirect  nature  of  the  con- 
cept we  are  able  to  form  as  to  what  manner  of  persons  we  are. 
Moreover,  all  the  ability  we  have  to  frame  a  concept  of  the  "  self  " 
is  dependent  upon  this  constant,  primary,  and  inexplicable  fact  of 
a  possible  reference  of  each  state  to  the  subject  of  the  state  (the 
"  I ").  To  explain  this  reference,  we  have  to  assume  that  it  has 
already  been  made  ;  we  have  to  assume  it  in  each  attempt  at  ex- 
planation. "We  may  express  the  absurdity  of  the  effort  to  think  or 
imagine  ourselves  out  of  the  reach  of  this  form  of  all  consciousness 
by  asking  ourselves  such  questions  as  follow :  How  can  there  be 
a  pain,  a  sensation,  a  thought,  an  act  of  will,  that  is  not  somebody's 
pain,  sensation,  thought,  or  act  of  will  ?  What  is  a  state  of  con- 
sciousness considered  as  separable,  or .  actually  separated,  from  a 
subject  of  such  state  ?  That  is  to  say,  no  state  of  consciousness 
can  even  be  conceived  of  that  does  not  involve  this  same  reference. 
There  may,  indeed,  be  great  doubt  whether  some  of  the  lower 
animals  ever  make  any  such  reference.  It  may  be  that  the  amoeba 
or  the  oyster  can  have  a  sensation  that  is  not,  quoad  sensation,  the 
conscious  state  of  the  amoeba  or  the  oyster.  As  to  this  we  cannot 
say.  But  we  can  say  that  if  such  a  so-called  sensation  is  possible 
for  any  animal,  it  is  impossible  for  us  to  imagine  it.  "We  cannot 
imagine  what  we  cannot  bring  under  the  unchanging  forms  of  our 
own  consciousness. 

The  force  of  the  foregoing  remarks  is  not  destroyed  by  calling 
attention  to  the  fact  that  the  attribution  of  the  state  of  conscious- 
ness to  the  subject  of  the  state,  to  the  "  I,"  is  by  no  means  con- 
tinually being  made.  It  is  plain  that  some  distinction  must  here 
be  drawn  between  being  conscious  and  being  self-conscious.     The 


EEFERElSrCE   TO   THE   EOO.  609 

crowd  intently  watching  a  tragedy  in  a  theatre,  or  a  conflagration, 
is  certainly  not  unconscious,  but  is  rather  in  an  exalted  state  of 
consciousness  ;  on  the  contrary,  he  who  is  intently  watching  the 
spectacle  is  not  at  all,  or  is  only  in  a  slight  degree,  se//"-conscious. 
There  are  considerable  periods  of  every  day  when,  so  far  as  we  can 
remember,  we  have  been  "conscious"  (not  being  in  profound  slum- 
ber or  having  fainted  away),  but  with  little  or  no  reference  in  con- 
sciousness of  its  activities  to  the  subject  of  them  all.  Nevertheless 
there  can  be  no  doubt  that  we  are  capable  of  this  reference  ;  that 
it  is  found  to  be  involved  in  every  mental  state  just  so  soon  as  we 
seek  to  determine  the  factors  of  such  state  ;  and  that  to  recognize 
its  being  there  is  essential  to  any  explanation  of  the  nature  of 
mind, 

§  19.  All  the  different  mental  phenomena  of  an  individual  must 
be  regarded  as  states  of  one  consciousness  ;  they  are  all  said  to  occur 
in  the  unity  of  consciousness.  There  can  be  no  doubt  that  every 
person  (with  the  exception,  at  most,  of  certain  rare  cases  of  so- 
called  double  consciousness)  attributes  all  the  forms  of  his  con- 
sciousness to  one  and  the  same  subject.  This  is  what  is  meant  by 
saying  that  he  regards  them  all  as  his  states.  We  cannot  conceive 
of  ourselves  as  dubitating  whether  some  particular  pain  or  pleasure, 
or  act  of  memory  or  of  imagination  or  of  will,  present  in  conscious- 
ness, is  to  be  ascribed  to  our  ego  or  not.  We  cannot  attribute  any 
such  state  to  some  other  than  our  own  ego.  It  is  true  that  in  cer- 
tain cases  of  disease  or  lesion  of  the  brain  an  abnormal  condition 
in  this  respect  seems  to  occur.  The  one  person  sometimes  seems 
to  pass  back  and  forth  between  two  mental  lives,  which  are  so 
distinct  from  each  other  that  they  may  well  be  said  to  belong  to 
two  personalities.  But  reflection  upon  these  abnormal  cases  only 
makes  the  stronger  and  clearer  our  conviction  as  to  the  unity  of 
consciousness.  Living  two  seemingly  distinct  mental  lives  is  not 
possible  without  its  being  assumed  that  each  one  of  the  two  is  lived 
in  the  unity  of  its  own  consciousness.  This  would  be  as  true  of 
twenty  distinct  lives,  if  they  followed  each  other  in  the  case  of  any 
individual  as  the  result  of  disease  of  the  bx-ain,  as  it  is  of  two  such 
lives. 

It  is  not  at  all  surprising  that  the  fact  of  the  primary  vrnitj  of 
consciousness  should  be  inexplicable  ;  for  it  is  itself  the  fact  im- 
plied and  assumed  in  all  attempts  at  exj)lanation  of  other  mental 
facts.  Were  this  the  line  of  thought  necessary  to  introduce  at  this 
point,  it  might  be  shown  that  all  the  unity  possessed  by  "Things  " 
is  dependent  upon  the  unity  of  consciousness.  Without  memory 
and  judgment  there  can  be  no  perception  of  Things.  But  the  bind- 
39 


610  MIND   AS   CONSCIOUS   BEING, 

ing  force  of  memory  is  dependent  upon  this  unity.  We  cannot 
remember  that  which  has  not  in  some  form  or  other  been  previously 
present  in  consciousness,  in  our  own  consciousness,  in  one  and  the 
same  consciousness  as  that  in  which  the  remembered  image  is  now 
present.  We  cannot  judge  except  by  uniting  two  terms  in  one  con- 
sciousness. 

Of  course,  all  language  as  to  the  unity  of  consciousness,  when 
carefully  examined,  turns  out  to  be  figurative,  and  to  have  no  mean- 
ing except  as  interpreted  over  from  entities  and  relations  of  a 
material  sort  into  terms  of  consciousness.  By  the  "  unity  of  con- 
sciousness "  it  cannot  be  meant  that  consciousness  is  some  kind  of 
an  entity  which  remains  one  and  unchangeable  throughout,  like 
those  atoms  which  physical  science  has  supposed  to  constitute  the 
whole  world  of  material  reality.  It  will  be  found,  however,  that  no 
conception  can  be  formed  of  the  unity  which  is  supposed  to  belong 
to  the  atom  without  involving  in  it  the  unity  of  consciousness. 
We  can,  indeed,  picture  to  ourselves  a  very  little  bit  of  extended 
matter,  barely  visible  under  the  highest  powers  of  the  microscope, 
Vv'hich  never  changes  its  shape  or  color,  etc.,  and  which  always  be- 
haves itself  in  exactly  the  same  way  under  precisely  similar  circum- 
stances. But  this  mental  picture  would  itself  have  any  unity  be- 
longing to  it  only  as  it  existed  in  the  unity  of  consciousness.  It  is 
this  unity  which  makes  each  "  Thing  "  to  be  one  thing  ;  it  is  this 
unity  which  imparts  to  all  else  that  is  one  whatever  unity  it  may 
have. 

When,  then,  we  speak  of  the  unity  of  consciousness  we  mean, 
fii-st  of  all  and  chiefly,  to  call  attention  to  the  following  primary 
fact  of  experience  :  All  states  of  consciousness  involve  a  reference 
of  the  state  to  an  "I,"  as  the  subject  of  the  state  ;  and,  in  spite  of 
the  constant  change  of  states  which  goes  on,  so  that  in  reality  the 
same  state  never  recurs,  and  even  the  same  thing  is  never  twice 
known,  all  the  states  are  understood  to  be  states  of  one  and  the 
same  subject.  This  reference  and  this  understanding  enter  into 
all  our  experience  ;  they  give  conditions  to  experience  and  make  it 
possible.  Whatever  changes  experience  may  be  conceived  of  as 
undergoing,  they,  as  conditions  of  all  possible  experience,  must  be 
conceived  of  as  remaining.  To  ask  us  to  try  to  imagine  a  mental 
state  or  act  not  involving  this  reference  and  understanding,  with 
respect  to  the  unit-subject  of  consciousness,  is  to  ask  us  to  try  to 
be  conscious  and  unconscious  at  the  same  time.  The  "  I "  may 
become  unconscious  ;  that  is,  the  phenomena  of  consciousness  in 
that  connected  development  which  characterizes  the  individual  may 
cease  to  exist.     But  phenomena  of  consciousness  cannot  be  con- 


KNOWLEDGE   OF   SELF   INDIRECT.  611 

ceivecT  of  as  occurring  without  being  referable  to  some  one  subject 
as  its  modes  or  states. 

§  20.  Metaphysics,  presuming  upon  its  intimate  relations  to  the 
"  old  psychology,"  has  doubtless  often  made  an  unwarrantable  use 
of  the  facts  above  mentioned.  It  has  often  declared  that  we  have 
an  immediate  and  indubitable  knowledge  of  the  mind  as  one  and 
the  same  real  being  in  all  acts  of  consciousness.  The  facts  have 
been  interpreted,  as  though  the  case  stood  as  follows  :  I  have  the 
power  to  look  within  myself,  and  by  thus  looking  I  can  discern 
what  I  really  am.  I  immediately  know  (that  is,  know  by  the  intro- 
spective act  of  self-consciousness)  that  "/"am  always,  however  my 
states  may  change,  one  and  the  same  real  being.  I  am  a  real,  self- 
identical  entity ;  and  if  asked  how  I  know  that  I  am  all  this,  ray 
appeal  is  to  the  indubitable  evidence  of  the  act  of  self-conscious- 
ness. 

The  foregoing  metaphysical  statement  of  the  case  is  by  no  means 
obviously  correct ;  we  believe  it,  on  the  contrary,  to  be  exaggerated 
and  incorrect.  In  thus  overstating  the  case,  there  is  liability  that 
the  case  itself  will  be  lost.  Consciousness  carries  with  it  no  immediate 
knowledge  of  any  real  and  self-identical  being — not  even  of  that  real 
being  which  we  call  Mind  and,  with  good  reason,  assume  to  exist 
as  the  ground  or  permanent  subject  of  mental  phenomena.  Meta- 
physics is  the  science  which  treats  of  those  assumptions  that  under- 
lie all  of  our  experience  with  what  we  call  "reality."  But  it  treats 
of  assumptions  or  beliefs  such  as  we  find  do  actually  and  inevita- 
bly enter  into  all  our  experience.  The  real  existence  of  "  Things," 
whether  of  the  masses  of  matter  we  daily  test  by  the  senses,  or  of 
those  hypothetical  beings  called  atoms  which  physical  science  re- 
quires in  order  to  account  for  the  phenomena,  depends  upon  such 
assumptions.  If  it  be  admitted  that  we  cannot  be  immediately 
conscious  of  ourselves  as  real  unit-beings,  we  are  no  worse  off  than 
we  are  with  respect  to  our  belief  in  the  existence  of  any  of  the  so- 
called  real  beings  of  which  all  men  suppose  the  world  to  be  com- 
posed. 

It  can  also  be  shown  that  the  case  of  the  mind  or  soul,  with  re- 
spect to  its  unity  as  a  real  being,  is  made  no  better  by  admitting 
that  an  immediate  consciousness  of  ourselves  as  such  unit-beings  is 
possible.  For  let  it  be  supposed  that  by  concentrating  all  my  at- 
tention upon  the  present  state  of  consciousness  I  most  clearly  and 
indisputably  discern  myself  as  one  real  being,  forming  the  ground 
of  that  state.  Let  it  be  supposed  that  every  half-hour  in  the  day  I 
repeat  this  mental  act.  It  would  still  have  to  be  assumed,  as  some- 
what altogether  out  of  consciousness,  that  the  real  being  discerned 


612  mijs^d  as  conscious  being. 

in  any  one  of  these  acts  of  introspection  is  one  and  the  same  real 
being  as  that  discerned  in  all  the  rest.  A  real  unit-being  that 
should  last  only  while  the  difficult  act  of  concentrated  introspec- 
tion was  taking  place  would  be  of  no  value  to  serve  as  a  self-con- 
scious mind.  In  fact,  such  a  unit-subject  of  the  individual  state 
would  have  no  claim  to  be  considered  as  a  real  being  at  all. 

§  21.  The  grounds  on  which  depends  the  assumption,  that  the 
subject  to  Avhich  all  the  phenomena  of  consciousness  are  actually 
referable  is  one  real  being,  will  be  considered  more  in  detail  at 
another  point.  For  the  present  we  merely  adopt  the  assumption, 
provisionally,  as  much  more  probable  than  any  which  accounts  for 
our  conscious  reference  to  such  subject,  by  enumerating  certain 
possible  relations  into  which  the  masses  and  molecules  of  the  brain 
may  be  thrown  as  conditions  of  the  empirical  unity  of  conscious- 
ness. That  there  is  such  empirical  unity  of  consciousness  there 
can  be  no  dispute.  Dispute  itself  would  assume  it.  It  scarcely 
admits  of  more  doubt  that  all  physical  theories  to  account  for  this 
unity  are  wholly  unsatisfactory.  We  know,  indeed,  certain  of  the 
physical  conditions  and  concomitants  of  consciousness.  If  oxygen- 
ated blood  is  shut  off  from  the  cerebral  substance,  consciousness 
disappears.  If  the  blood  has  floating  in  it  certain  drugs,  or  prod- 
ucts of  the  combustion  of  tissue,  consciousness  is  disturbed.  If 
certain  cerebral  areas  are  injured  or  eradicated,  the  psycho-physi- 
cal basis  of  certain  forms  of  consciousness  is  altered.  Still,  all 
this  does  not  seem  to  bring  us  a  step  nearer  a  satisfactory  physical 
account  of  the  unity  of  consciousness.  The  molecules  of  the  brain 
are  infinitely  numerous  ;  they  are  made  up  into  structural  forms  of 
indefinite  number  and  variety  ;  the  kinds  of  the  relations  they  as- 
sume toward  each  other  are  indescribably  many.  Consciousness, 
so  far  as  we  know,  has  no  special  centre  or  seat  within  the  cere- 
brum ;  and  if  it  had,  the  constituents  and  activities  of  that  centre 
would  have  to  be  exceedingly  manifold  and  complex.  Now,  all 
this  is  precisely  the  opposite  of  what  we  should  expect  of  a  phys- 
ical structure  which  should  be  called  upon  to  exhibit  the  phenom- 
ena of  many  conscious  states,  all  referable  to  one  subject.  No  help 
toward  solving  the  problem  is  derived  from  calling  attention  to 
the  fact  that  the  different  portions  and  elements  of  the  brain  are 
all  interconnected.  The  connecting  structures  only  add  still  fur- 
ther to  its  multiplicity  and  complexity  of  elements.  It  would  be 
easier  to  conceive  of  an  atom  as  becoming  conscious  than  the  cer- 
ebral cortex, 

§  22.  But  surely  the  assumption  that  one  real  being  is  the  sub- 
ject of  these  states,  which  are   certainly  all  referable  in  conscious- 


MIND   A   EEAL   UNIT-BEIISTG.  613 

ness  to  one  and  the  same  subject,  is  not  an  impossible  one.  On 
the  contrary,  it  is  the  most  natural  assumption  ;  it  is  the  assump- 
tion instinctively  made  by  men  in  general.  Notwithstanding  the 
difficulties  which  encompass  it  as  soon  as  we  attempt  to  define  it, 
or  to  test  the  ground  on  which  it  rests,  we  shall  find  that  it  is  de- 
fensible and  valid. 

We  conclude,  then,  from  the  previous  considerations  :  The  sub- 
ject of  all  the  states  of  consciousness  is  a  real  unit-heing,  called  Blind  ; 
ivhich  is  of  non-material  nature,  and  acts  and  develops  according  to 
laws  of  its  own,  but  is  specialhj  correlated  loith  certain  material  mole- 
cular and  masses  forming  the  substance  of  the  Brain. 


CHAPTER   II. 
THE    DEVELOPMENT    OF    THE    MIND. 

§  1.  A  DISTINCTIVE  feature  of  modern  science  is  its  endeavor  to 
satisfy  inquiry  into  the  nature  of  the  objects  of  its  investigation  by 
a  detailed  description  of  their  development.  In  answer  to  the  in- 
quiry what  a  thing  is,  we  are  invited  to  listen  to  an  account  of  how 
it  hecavie  what  it  is.  Indeed,  the  universal  process  of  "  Becoming  " 
has  been  almost  personified  and  deified  so  as  to  make  it  the  true 
gi'ound  of  all  finite  and  concrete  existences.  There  can  be  no 
doubt  as  to  the  great  fruitfuluess  and  value  of  this  historical  and 
genetic  way  of  studying  everything.  Any  complex  existence  is  cer- 
tainly far  better  understood  after  it  has  been  not  simply  analyzed 
into  its  jjresent  component  parts,  but  has  also  been  traced  back  to 
its  most  nearly  primitive  and  undifferentiated  stages.  The  history 
of  the  egg  explains  the  bird  even  more  than  the  nature  of  the  bird 
'explains  the  egg. 

Both  of  the  two  subjects,  with  whose  correlations  Physiological 
Psychology  deals,  require  for  their  most  satisfactory  understanding 
to  be  studied  by  this  genetic  method.  The  structure  of  the  nervous 
system  appears  in  a  new  light  when  regarded  as  the  result  of  a  pro- 
cess of  evolution.  Beginning  with  the  unimpregnated  ovum,  by 
propagation  of  cells  of  living  protoplasm,  by  segmentation  of  larger 
sections  of  these  cells,  by  prolifei'ation  of  cells  and  separation  into 
layers,  the  one  portion  of  the  gei'm  from  vv^hich  the  mechanism  of 
nerve-fibres  and  nerve-cells  is  to  unfold  itself  becomes  differentiated 
from  the  other  portions.  By  vital  processes  kept  up  through  nutri- 
tion and  resulting  in  the  growth  of  some  areas  beyond  others,  and 
by  mechanical  influences  at  work  to  crowd  forward  here  or  push 
back  there,  to  fold  and  tuck  and  cause  to  dip  or  curve,  etc.,  this 
epiblastic  portion  develops  the  system  of  end-organs,  central  or- 
gans, and  connecting  tracts  of  nerves. 

Psychology,  also,  has  felt  strongly  this  modern  impulse.  It  has 
been  forced  to  confess  that  its  real  task  is  but  begun  when  it  has, 
by  introspection,  examined  and  classified  the  j^henomena  of  adult 
conscious  Ufe.     All  the  mental  phenomena  undoubtedly   have  a 


MENTAL   FACULTIES    PROGRESSIVE.  613 

truly  vital  connection.  Those  of  the  present  have  their  roots  in 
those  of  the  past.  The  so-called  faculties  of  the  mind  are  neither 
hard  and  fixed  lines  drawn  to  exclude  from  internal  relation  the 
various  modes  of  its  behavior  in  consciousness,  nor  are  they  kinds 
of  activities  that  spring  up,  full-formed  at  once,  at  different  in- 
tervals in  its  entire  history.  Although  we  can  never  reproduce 
in  adult  self-consciousness  the  forms  of  the  earliest  stages,  we 
can  show  that  these  forms  differed  greatly  from  those  taken  in 
this  adult  self-consciousness.  We  can  show  that,  the  earlier  forms 
must  have  been  much  the  simpler.  For  exam.ple,  an  analysis  of 
the  presentations  of  sense  shows  that  the  "things"  of  developed 
experience  are  resolvable  into  certain  elements  of  sensation  which 
the  mind  has  learned  to  localize.  In  other  words,  perception  is  a 
result  of  development ;  for  "things"  are  not  ready-made  products 
existing,  as  they  appear,  outside  of  the  mind,  but  resultants  of 
mental  activities  that  have  to  be  performed  anew  so  often  as  the 
things  appear.  It  is  in  the  evolution  of  the  mind  that  we  find  our 
means  for  understanding  its  true  nature.  Moreover,  the  character- 
istics which  distinguish  one  mind  from  another  are  to  be  under- 
stood as  largely  resulting  from  the  order  and  relative  prominence 
of  different  activities  in  the  development  of  each. 

§  2.  So  far  as  the  connection  of  mental  phenomena  with  the  in- 
creasing complexity  of  the  nervous  activities,  and  with  the  stored 
energies  and  hardening  habitus  of  the  nervous  elements,  affords  any 
explanation  of  the  development  of  the  mind,  we  have  already  said 
all  that  is  necessar3^  The  growth  of  the  mind  in  the  acquirement 
and  arrangement  of  sensations,  in  the  recalling  of  ideas,  in  the 
forming  of  judgments  about  objects  of  sense,  etc.,  is  plainly  de- 
pendent upon  the  evolution  of  the  bodily  members.  But  the  nat- 
ure of  the  relation  which  exists  between  the  mental  phenomena 
and  the  nervous  mechanism,  so  far  as  this  can  be  learned  by  study- 
ing the  development  of  both,  furnishes  us  with  another  question. 
Upon  this  question,  also,  the  same  conflict  of  view  as  that  to  which 
we  have  already  drawn  attention  may  arise.  On  the  one  hand,  the 
attempt  is  made  to  refer  all  the  so-called  development  of  the  mind 
to  the  evolution  of  the  substance  of  the  brain,  under  purely  physi- 
cal and  mechanical  causes.  This  attempt,  then,  denies  that  any 
real  unit-being  called  the  Mind  needs  to  be  assumed  as  undergoing 
a  process  of  development  according  to  laws  of  its  own.  It  cannot 
be  disputed  that  many  facts  of  experience  tend  to  strengthen  such 
an  attempt. 

There  is  a  general  correspondence,  with  respect  to  the  complex- 
ity and  quality  of  the  work  done,  between  the  different  stages  in 


616  MIND   AS    A   DEVELOPMENT. 

the  development  of  both  body  and  mind.  Nervous  system  and 
mental  condition  are  both  immature  in  infancy ;  both  develop  with 
great  rapidity  in  early  childhood,  and  then  more  slowly  on  into 
adult  life  ;  both — it  is  claimed — remain  comparatively  stationary 
through  the  period  of  man's  highest  maturity  ;  and  as  old  age  ad- 
vances, both  keep  pace  in  their  decline.  Moreover,  cases  of  arrested 
development  of  brain  are  cases  of  arrested  development  of  mind. 
Idiots  are  frequently  microcephalic  ;  many  of  them  have  brains 
weighing  less  than  thirty  ounces.  Degeneracy  of  the  tissues  of  the 
cerebral  hemispheres  is  commonly  connected  with  increasing  de- 
generacy of  the  mind.  As  the  tides  of  molecular  nerve-commotion 
rise  and  fall  in  the  nervous  mass,  so  rise  and  fall  the  tides  of  men- 
tal vigor.  A  temporary  increase  of  cerebral  action,  caused  by  a 
glass  or  two  of  wine,  is  expressed  in  the  form  of  mental  phenomena 
by  a  heightening  of  imagination,  a  quickened  flow  of  ideas.  What 
need,  then — it  is  asked — of  assuming  any  permanent  subject  of 
what  we  regard  as  mental  development,  other  than  the  mechanism 
of  physical  molecules  with  its  evolution  under  the  control  of  physi- 
cal law  ? 

On  the  other  hand,  all  attempts  to  account  for  the  orderly  in- 
crease in  complexity  and  comprehensiveness  of  the  mental  phe- 
nomena by  tracing  the  physical  evolution  of  the  brain  are  wholly 
unsatisfactory  to  many  minds.  We  have  no  hesitation  in  classing 
ourselves  among  this  number.  Those  facts  of  experience  which 
show  a  correspondence  in  the  order  of  the  development  of  the  body 
and  the  mind,  and  even  a  certain  necessary  dependence  of  the  lat- 
ter upon  the  former,  are,  of  course,  to  be  admitted  ;  but  they  are 
equally  compatible  with  another  view  of  the  mind's  development. 
This  other  view  has  the  additional  advantage  that  it  makes  room 
for  many  other  facts  of  experience  which  are  very  difficult  of  rec- 
onciliation with  any  materialistic  theory.  On  the  whole,  the  his- 
tory of  each  individual's  experience  is  such  as  requires  the  assump- 
tion that  a  real  unit-being  (a  Mind)  is  undergoing  a  process  of  de- 
velopment, in  relation  to  the  changing  condition  or  evolution  of 
the  brain,  and  yet  in  accordance  with  a  nature  and  laws  of  its  own. 

^  3.  That  the  development  of  a  real  non-material  being  is  im- 
plied in  the  history  of  the  mental  phenomena  of  each  person  may 
be  argued  on  two  principal  grounds.  In  the  first  place,  it  may  be 
shown  that  the  stages  and  laws  of  the  development  of  mind  do  not 
fully  correspond  to  those  which  are  observed  on  tracing  the  evolu- 
tion of  the  nervous  system.  It  may  also  be  shown  that  certain  ele- 
ments necessarily  enter  into  the  development  of  mind,  which  have 
nothing  like  them,  or  strictly  correlated  with  them,  in  the  evolu- 


EEALITY   OF   MENTAL   HISTORY.  617 

tion  of  the  material  mechanism.  One  real  being  may  be  dependent 
on  other  beings  for  its  starting,  as  it  were,  and  for  certain  factors 
that  enter  into  its  growth  or  furnish  the  indispensable  conditions 
of  its  growth.  It  may  thus  receive  the  form  and  direction  of  its 
development,  in  large  measure,  fi'om  these  other  beings.  And  yet 
this  fact  gives  us  no  right  whatever  to  refuse  to  such  a  being  all 
title  to  take  rank  among  other  real  existences  with  a  complex  nat- 
ure of  its  own.  No  existence  loses  or  impairs  its  claim  to  reality 
by  being  dependent  for  its  development  on  other  existences.  The 
mind,  on  the  contrary,  most  indubitably  establishes  such  a  claim, 
because  the  stages  and  laws  of  its  unfolding,  and  some  of  the 
factors  which  necessarily  enter  into  this  unfolding,  are  peculiar  to 
itself  (sai  generis). 

§4.  That  the  words,  "development  of  the  Mind,"  stand  for  a 
real  process,  there  can  be  no  reasonable  doubt.  The  sum-total  of 
the  conscious  experience  of  each  individual  is  something  far  more 
than  a  mere  series  of  states  of  consciousness.  No  difference  in  de- 
grees under  the  same  kind  can  be  conceived  of  which  is  greater 
than  the  difference  between  the  most  mature  and  highly  developed 
mental  performances  and  those  inconceivably  simple  activities  with 
which  the  mental  life  begins.  So  far  as  the  character  of  the  phe- 
nomena of  consciousness  is  concerned,  the  mind  of  the  adult  New- 
ton or  Kant  is  much  farther  removed  from  the  mind  of  the  infant 
Newton  or  Kant  than  the  latter  is  fi'om  the  mind  of  one  of  the 
lower  animals.  There  is  much  more  which  is  companionable  and 
mutually  intelligible  between  the  adult  man  and  his  dog  than  be- 
tween the  adult  man  and  his  newly  born  child.  The  latter  is, 
however,  raised  at  once  above  the  most  intelligent  animal  when 
we  consider  the  possibilities  of  its  mental  development.  What  the 
human  being  is  cannot  be  at  all  adequately  described  without  con- 
sidering the  nature  and  limits  of  that  process  of  becoming  which 
belongs  to  it. 

There  is  no  doubt,  also,  that  the  incomparable  improvement  of 
the  mental  processes  which  distinguishes  the  adult  from  the  infantile 
human  being  is  a  true  development.  Each  stage  of  this  improve- 
ment is  dependent  upon  preceding  stages.  The  changes  are  aU  in 
some  sort  according  to  a  plan.  Thus  the  life  of  every  individual's 
mental  experience  is  capable  of  being  made  into  a  history.  A  cer- 
tain tolerably  uniform  order  in  the  relative  development  of  the  dif- 
ferent faculties  is  discernible.  At  first  the  senses  are  awakened  to 
a  lively  and  varied  activity  ;  then  memory  and  imagination  become 
more  prominent  ;  and,  finally,  judgment  and  the  reasoning  powers 
assert  their  sway.     Gradually,  things  become  known  and  conduct 


618  MIND    AS   A   DEVELOPMENT. 

shaped  under  principles  which  are  assumed  to  have  a  universal 
vahdity  as  so-called  general  laws.  The  history  of  the  mental  life 
of  every  human  being,  from  the  cradle  (or  even  from  its  embryonic 
existence)  to  the  grave,  has  all  these  characteristics  of  unfolding 
itself  in  a  regular  order,  in  which  all  that  comes  at  all  comes  in 
due  sequence  and  acknowledged  dependence  upon  what  has  pre- 
ceded.    This  is  the  very  essence  of  a  true  development. 

§  5.  Can  the  development  of  the  mind  be  explained  as  merely 
the  I'esultant  or  expression  of  the  physical  evolution  of  the  nervous 
system — this  system  being  regarded  as  situated  in  the  rest  of  the 
bodily  environment,  and  surrounded  by  the  more  extended  envi- 
ronment of  the  world  of  active  physical  energies  outside  ?  Against 
an  affirmative  answer  to  this  inquiry  stand  many  facts  and  laws  of 
all  such  mental  development.  In  spite  of  what  must  be  said  con- 
cerning the  striking  correspondence  between  the  evolution  of  the 
bodily  organism  and  the  development  of  the  mental  powers,  it 
must  be  held  that  there  are  marked  divergences  as  Avell.  At  cer- 
tain epochs  of  life  the  evolution  of  the  brain  seems  to  stand  far  in 
advance  of  the  mind ;  at  others,  the  mind  appears  to  have  over- 
taken and  passed  by  the  stage  reached  by  its  physical  substratum. 
During  a  long  period  of  life  the  growth  of  mental  powers  is  con- 
stant and  solid,  while  the  growth  of  the  physical  basis  has  nearly 
ceased,  and  such  changes  as  are  taking  place  in  it  appear  quite 
inadequate  to  serve  as  correlates  for  the  mental  growth.  More- 
over, the  most  distinctly  typical  features  in  the  develojDment  of  the 
mind  remain  the  same  when  malformation  or  disease  or  accident 
have  largely  changed  the  physical  evolution  of  the  brain. 

§  6.  We  have  no  sufficient  means  for  deciding  how  far  the  mental 
life  of  the  human  embryo  keeps  pace  with  its  organic  evolution. 
We  do  not  even  know  beyond  doubt  that  the  embryo  has  a  mental 
life,  in  the  only  tenable  meaning  of  the  words — that  is,  a  life  of 
conscious  states.  But  it  is  probable  that  its  antenatal  movements 
are  not  all  purely  reflex,  and  neither  accompanied  nor  directed  by 
conscious  sensation,  feeling,  and  volition.  The  mental  life  of  the 
embryo,  if  it  exist  at  all,  can  hardly  be  more  than  an  irregular  and 
fitful  succession  of  the  lowest  and  least  complex  mental  phenomena. 
Taste,  smell,  hearing,  and  sight  are,  of  course,  not  to  be  thought 
of  as  entering  into  such  a  mental  life.  Touch,  as  we  understand 
the  word  to  express  the  localized  sensations  of  pressxire  which  arise 
through  the  practised  organ  of  the  skin,  is  scarcely  more  likely  to 
belong  to  the  human  embryo.  Obscure  feelings  arising  from 
changes  in  its  relation  to  the  surrounding  tissues  and  fluids  of  the 
mother,  or  from  disturbances  in  its  own  internal  organs,  and  result^ 


THE   AROUSING   OF  THE   MIND.  619 

ing  equally  obscure  feelings  of  innervation,  as  its  limbs  are  moved, 
must  constitute  the  great  part  of  its  experiences.  As  yet  there  is 
no  experience,  properly  so  called  ;  no  perception  of  things,  no  feel- 
ing of  self,  no  discrimination  of  ego  and  state.  Yet  long  before 
the  child  is  born  it  possesses  a  wonderfully  elaborate  nervous 
mechanism,  far  surpassing  in  its  grade  of  evolution  the  nervous 
system  of  the  most  intelligent  adult  animals.  Previous  to  birth 
this  nervous  mechanism  must  also  be  constantly  in  action  in  a 
highly  complicated  way  ;  it  is  engaged  in  supervising  the  processes 
of  nutrition,  and  in  the  reflex  and  automatic  activities  which  are 
expressed  by  the  changes  of  the  child's  position  within  the  womb 
of  the  mother.  The  mind,  however,  is  as  yet  unawakened  ;  this  is 
not  because  the  nervous  mechanism  is  not  complex  and  active 
enough  to  serve  as  the  physical  basis  of  a  rich  mental  development, 
but  because  the  kinds  of  sensation — visual,  tactual,  auditory,  etc. — 
which  start  and  furnish  and  direct  this  development  have  not  yet 
been  supplied.  The  mental  life  cannot  then  be  said  to  have  kept 
pace  before  birth  with  the  evolution  of  the  brain,  or  with  its  dis- 
tinctive activities.  On  the  contrary,  it  is  far  behind  the  stage  al- 
ready reached  by  its  physical  support.  It  waits  to  he  aroused  and 
set  to  its  own  work  of  combining  and  interpreting  those  sensations 
which  are  to  serve  as  its  chief  means  of  early  culture. 

For  the  first  few  weeks  of  infancy  the  same  relation  between  the 
relative  development  of  the  body  and  soul  of  the  child  is  maintained. 
Both  are  subjects  of  a  rapid  growth,  but  the  former  is  still  much  in 
advance  of  the  latter.  The  newly  born  infant  is,  in  respect  to  the 
condition  of  its  nervous  system,  much  the  most  highly  oi-ganized 
and  fully  equipped  of  all  young  animals  ;  but  as  judged  by  the 
number  and  quality  of  its  volitions  and  perceptions,  many  other 
young  animals  are  less  stupid  and  insensate.  If  we  may  represent 
its  mental  condition  by  anything  conceivable  through  the  adult 
imagination,  the  human  infant  is  in  a  dreamless  sleep  occasionally 
interrupted  by  instants  of  unlocalized  and  unmeaning  sensations. 

The  cavity  of  the  infant's  tympanum  is  filled  with  a  fluid,  the 
place  of  which  is  only  gradually  taken  by  the  air.  Sensations  of 
sound,  if  they  arise  at  all,  must  be  at  first  only  occasional  and 
faint.  Binocular  movements  of  the  eyes  in  the  direction  of  bright 
objects  take  place  early  ;  and  it  is  through  sensations  of  light  and 
color  that  the  first  activities  of  the  mind  in  perception  are  aroused 
and  controlled.  But  for  some  weeks  there  ai-e  only  sensations  and 
impressions,  without  tme  perceptions  ;  there  is  as  yet  no  knowl- 
edge of  any  "  Thing."  This  earliest  relation  of  mind  and  brain, 
with  respect'  to  the  degree  and  rate  of  their  development,  is  not 


620  MIND   AS   A  DEVELOPMENT. 

favorable  to  any  form  of  the  materialistic  theory.  It  rather  favors 
the  view  that  the  mental  phenomena  belong  to  another  principle 
than  any  material  substratum.  The  dependence  of  the  mind  on 
the  brain  is  indirect  and  through  the  sensations  (chiefly  of  sight 
and  touch)  which  must  be  furnished  to  the  mind  as  the  primary 
factors  in  its  development.  The  halt  in  the  development  of  mind 
at  first,  and  its  distinct  backwardness  with  respect  to  the  relative 
stage  it  has  reached,  are  due  to  a  lack  of  such  sensations  as  have 
the  characteristics  of  spatial  series  (see  Part  II.,  chap.  VI.),  and  so 
are  able  to  stimulate  the  mind,  and  afford  it  the  requisite  material 
for  the  construction  of  true  presentations  of  sense. 

§  7.  Within  a  few  months  after  birth  the  child  has  undergone 
an  enormous  mental  development ;  it  has  become  a  mind,  in  some 
inchoate  way  recognizing  itself  as  the  subject  of  states,  and  per- 
ceiving a  little  surrounding  world  of  objects  of  sense.  It  has  also 
begun  to  attend  to  the  objects  presented  in  consciousness,  and  to 
direct  its  attention  by  voluntary  choice.  The  mind's  relating  ac- 
tivity has  been  aroused  ;  and  acts  of  memory,  discrimination,  and 
judgment,  as  the  basis  for  those  concepts  which  require  articulate 
language  to  express  them,  are  repeatedly  taking  place.  The  as- 
sumptions of  reason,  as  involved  in  all  human  experience  of  things, 
and  of  their  action  and  reaction  upon  each  other,  are  found  to  be 
shaping  the  growth  of  the  mental  powers. 

As  accompanying  and  forming  the  ground  for  this  sudden  blos- 
soming of  the  mind  in  the  use  of  its  conscious  powers,  there  is  a 
continuous  and  yet  diminishing  monthly  increase  of  the  substance 
of  the  brain.  No  new  organs  are  formed  within  the  cranial  cavity  ; 
but  those  which  have  been  formed  previous  to  birth  are  further 
developed  under  the  changed  conditions  of  nutrition.  In  respect  to 
the  quantity  and  arrangement  of  its  molecules,  the  nervous  mech- 
anism certainly  undergoes  no  development  during  the  first  year  of 
the  child's  life  which  at  all  corresponds  to,  or  accounts  for.  the 
development  of  the  child's  mind. 

It  may  be  claimed,  however,  that  the  most  important  develop- 
ment of  the  nervous  mechanism  has  been  overlooked  in  the  fore- 
going description.  This  development  does  not  consist  so  much  in 
the  increased  quantity  of  the  brain's  substance,  or  in  the  more 
intricate  arrangement  of  its  elements  with  relation  to  each  other. 
It  consists  rather  in  the  forming  of  what  has  already  been  alluded 
to  (Part  n.,  chap.  X.,  §§  18  f.)  as  "  dynamical  associations  "  among 
the  existing  elements.  The  statement  that  such  is  the  nature  of 
the  developing  activities  of  the  nervous  mechanism,  and  the  as- 
sumption that  such  activities  are  an  indispensable  physical  condi- 


FORM  ATI  ON   OF   ASSOCIATIONS.  621 

tion  for  the  growth  of  the  mind,  may  both  be  taken  for  granted. 
But  even  then  the  argument  is  far  from  complete  upon  which  the 
development  of  mind  as  a  real  being,  with  a  nature  of  its  own,  and 
with  a  history  controlled  by  its  own  laws,  is  denied.  The  forma- 
tion of  the  so-called  "dynamical  associations"  among  the  mole- 
cules of  the  nervous  mass  furnishes  no  adequate  account  of  the 
development  of  mind.  This  development  is  not  in  the  direction 
simply  of  associating  together  states  of  feeling,  each  one  of  which 
has  an  exact  physical  correlate  in  a  physical  association  among  the 
molecules  of  nervous  substance.  It  is  rather  a  development  which 
for  its  very  existence  requires  something  different  from  such  asso- 
ciations. The  child  might  go  on  forever  merely  associating  together 
affections  of  its  own  mind  in  correspondence  to  dynamical  associa- 
tions among  the  nervous  molecules,  and  yet  have  no  growth  of  ex- 
perience such  as  it  actually  attains.  The  fact  is  that  within  a 
single  year,  or  within  two  years,  the  child  has  learned  to  know 
"Things,"  to  attend  to  some  in  preference  to  others,  to  refer  its 
states  in  some  crude  way  to  itself,  to  form  concepts  and  judgments 
by  the  mind's  relating  activity,  and  to  underlay  the  world  of  its 
sensuous  experience  with  another  world  of  assumption  respecting 
certain  non-sensuous  realities.  To  account  for  this  boundless  ex- 
pansion of  the  activities  of  consciousness,  with  its  surprising  new 
factors  and  mysterious  grounds  of  synthesis  and  assumption,  by 
proposing  an  hypothesis  of  "dynamical  associations"  among  the 
particles  of  nervous  substance  in  the  brain,  is  a  deification  of  im- 
potency.  So  far  as  we  really  know  anything  about  the  development 
of  both  brain  and  mind,  we  are  compelled  to  say  that  the  latter, 
when  once  started  by  the  sensations  furnished  through  excitation 
of  the  former,  proceeds  to  unfold  its  activities  with  a  rapidity  and 
in  an  order  for  which  no  adequate  physical  causes  can  be  assigned. 

During  the  period  of  young  manhood,  or  young  w^omanhood,  the 
dependence  of  the  development  of  the  mind  on  that  of  the  body 
is  most  strikingly  seen  in  the  influence  over  the  emotions  and 
imagination  from  the  sudden  unfolding  of  certain  bodily  organs 
and  powers.  The  indirect  influence  of  these  acts  of  feeling  and 
imagination  upon  the  more  purely  intellectual  progress  of  the  mind 
is,  of  course,  correspondingly  great.  But  the  dependence  of  mind 
on  body  is  by  no  means  such  as  to  favor  the  view  that  there  is  no 
ground  in  a  real  being,  other  than  the  brain,  for  the  order  and  rate 
of  the  mental  development. 

This  same  statement  is  emphatically  true  of  the  long  period  of 
maturity  which  constitutes  what  we  call  the  "middle  life  "  of  man. 
During  this  time  the  nervous  matter  undergoes  scarcely  any  dis- 


622  MIND   AS   A   DEVELOPMENT. 

cernible  development.  Nothing  that  microscope  or  electrometer 
can  detect  distinguishes  the  brain  of  the  man  of  twenty-five  from 
that  of  the  man  of  fift3\  A  few  grammes  of  weight  have  perhaps 
been  added  to  it  during  this  long  period  of  years.  Anyone  is  at 
liberty  to  speculate  as  to  the  immense  development  of  so-called 
"dynamical  associations"  which  has  taken  place  during  the  same 
period.  We  are  far  from  denjdng  the  possibility  of  such  develop- 
ment. But  the  fact  that  a  large  development  of  mind  may  have 
taken  place  during  the  same  period  cannot  be  denied.  If  it  be 
true  that  large  numbers  of  mankind  remain  mentally  stationary  for 
most  of  their  adult  life,  this  truth  in  no  way  favors  a  materialistic 
view  of  the  development  of  mind.  Most  observing  persons  will 
rightly  find  the  chief  account  of  the  failure  of  mental  growth  in 
precisely  those  kinds  of  mental  activity  which  least  admit  of  being 
explained  by  physical  analogies.  It  is  from  want  of  mental  curiosity, 
attention,  careful  and  comprehensive  judgment,  sound  moral  pur- 
pose, etc.,  that  most  men  fail  to  develop  during  adult  life  in  their 
mental  powers.  And  these  ai*e  mental  activities  for  explaining 
which  no  one  as  yet  has  been  able  to  conjecture  any  analogous  or 
corresponding  class  of  cerebral  changes. 

Many  minds,  however,  not  only  make  vast  acquisitions,  but  also 
experience  a  large  unfolding  of  mental  capacities  during  the  period 
of  middle  life.  How  mature  and  wide-reaching  do  the  judgments 
of  some  men  then  become !  How  profound  the  insight  into  the 
most  abstract  and  difficult  speculations  comes  to  be !  What  cere- 
bral evolution  shall  be  conceived  of  as  being  the  only  true  cause, 
and  the  exact  physical  correlate,  of  the  mental  development  of  Kant 
during  the  years  preceding  the  appearance  of  the  "Critique  of  Pure 
Reason,"  or  of  Newton  while  he  was  unfolding  the  calculations  and 
conjectures  of  the  "PrinciiDia?"  To  hold  that  the  changing  mole- 
cules of  the  brain-substance  of  these  thinkers  were  the  sole  subjects, 
really  being  and  acting  in  the  unrolling  of  these  great  dramas  of 
human  speculations,  involves  an  astonishing  credulity.  On  the 
contrary,  we  seem  compelled  to  affirm  that  no  important  activity, 
or  law,  or  fact,  in  the  order  of  such  mental  development,  fails  to 
demand  the  assumption  of  a  real  and  non-material  unit-being,  un- 
folding its  powers  according  to  its  own  nature,  although  in  de- 
pendence upon  certain  elements  and  conditions  furnished  through 
the  brain. 

§  8.  Advancing  old  age  is  doubtless,  as  a  rule,  characterized  by 
a  simultaneous  decline  both  of  certain  mental  and  of  certain  bodily 
powers.  In  this  period  of  life,  howevei",  the  correspondence  be- 
tween the  changes  in  the  character  of  the  phenomena  of  conscious- 


'        THE   FIISTAL   MEISTTAL   STAGE.  623 

ness  and  tlie  altered  vigor  and  quality  of  the  nervous  mechanism  is 
not  such  as  to  suggest  that  the  two  have  an  altogether  common 
basis.  In  healthy  normal  old  age  the  course  of  the  mental  life  is 
distinguished  chiefly  by  the  dropping  out  or  diminished  action  of 
certain  factors  that  are  relatively  prominent  in  youth.  The  circu- 
lation is  slower  ;  the  vital  energy  is  declining  ;  the  muscles  are  less 
promptly  and  completely  under  the  control  of  the  volitions  ;  the 
end-organs  of  sense  are  less  sensitive  under  impressions  ;  and 
certain  emotions  and  passions  whose  physical  basis  is  of  the  most 
obvious  sort  become  greatly  modified  or  disappear.  As  to  the 
marked  effect  of  these  bodily  changes  upon  the  mental  development 
there  can  be  no  doubt ;  and  if  the  previous  mental  development  has 
been  chiefly  along  lines  indicated  by  organic  activities  the  apparent 
decay  of  mental  vigor  when  the  physical  basis  begins  to  fail  is,  of 
course,  also  most  plainly  marked. 

On  the  other  hand,  there  are  many  other  cases,  where  no  notable 
difference  can  be  detected,  or  even  fairly  assumed,  in  the  course  of 
the  psychical  evolution  down  to  the  "  feebleness  "of  old  age ;  where 
the  course  of  mental  development  continues  substantially  undis- 
turbed in  all  its  most  important  features.  The  mind  of  the  culti- 
vated old  man,  with  calm  and  broad  judgment,  with  refined  kind- 
liness and  fixed  moral  principles,  is  not  to  be  spoken  of  as  suffering 
a  decline  which  keeps  pace  with  the  failing  of  his  physical  powers. 
It  maj  justly  be  claimed  that  the  final  period  of  human  life,  on  the 
whole,  favors  that  theory  which  regards  the  mind  as  by  no  means 
wholly  conditioned  upon  the  brain  for  the  character,  order,  and 
laws  of  its  development. 

§  9.  The  same  general  view  of  the  development  of  mind,  which 
is  most  consistent  with  the  facts  of  the  different  stages  of  life,  is 
also  favoxxd  by  considering  those  sudden  checks  or  changes  in  the 
course  of  this  development  that  are  caused  by  disturbing  or  de- 
stroying considerable  portions  of  the  nervous  matter.  The  phe- 
nomena which  follow  experimental  extirpation  of  the  substance  of 
the  brain  in  the  lower  animals,  and  loss  of  it  by  serious  lesions  in 
the  case  of  man,  do  not  favor  a  materialistic  theory  of  mental  de- 
velopment (see  Part  11.,  chaps.  I.  and  II.).  Extensive  losses  in 
certain  areas  of  the  cerebral  hemispheres  are  often  followed  by 
no  appreciable  disturbance  even  of  any  sensory  or  motor  activity. 
When  lesions  are  followed  by  such  disturbance,  their  effects  may 
in  time  wholly  or  partially  disappear.  When  such  disturbance  is 
permanent,  it  is  not  necessarily  connected  with  loss  in  the  power 
of  judgment,  in  the  higher  intellectual,  aesthetic,  and  ethical  activi- 
ties of  feeling,  intellect,  or  will.     Even  where  aphasia  is  so  severe 


624  MIISTD   AS   A   DEVELOPMENT. 

as  to  include  the  loss  of  all  power  to  utter  or  understand  articulate 
language,  the  patient  may  still  show  a  good  degree  of  mental  acute- 
ness  by  ability  to  make  calculations  or  play  games  of  skill. 

On  the  other  hand,  the  much  more  serious  interruption  or  com- 
plete loss  of  mental  development  may  occur  when  no  adequate  ex- 
planation can  be  detected  in  the  distui'bance  or  arrest  of  cerebral 
development.  It  is,  of  course,  natural  to  conjecture  that,  in  all 
this  latter  class  of  cases,  more  accurate  information  would  show  us 
some  diseased  condition  of  the  brain  as  the  physical  antecedent  of 
the  mental  defects.  We  know  that  subtle  changes  in  the  character 
of  the  blood-supply,  such  as  we  have  no  physical  means  whatever 
for  detecting,  are  often  the  causes  of  most  profound  changes — 
either  temporary  or  more  permanent — in  the  train  of  ideas.  None 
the  less,  however,  do  both  classes  of  cases  above  mentioned  favor 
the  theory  we  are  advocating,  rather  than  the  so-called  materialistic 
theory  of  mind. 

§  10.  All  the  foregoing  considerations  suggest  the  conclusion 
that  the  mind  is  primarily  and  chiefly  dependent  in  its  develop- 
ment upon  the  nervous  mechanism  for  furnishing  and  directing 
the  combination  and  order  in  recurrence  of  those  sensations  which 
enter  into  all  presentations  of  sense.  Let  any  person  of  normal 
and  sane  brain  and  mind  consider  how  intimate  and  extensive  is 
the  connection  between  his  sensations  and  his  whole  mental  devel- 
opment. Fickle  and  confused  experience  of  sensation  involves 
fickleness  and  confusion  of  judgment  on  all  matters  of  sense.  Loss 
of  any  class  of  sensations,  as  a  whole  or  in  part,  involves  a  distinct 
impairment  of  mental  powers.  Such  loss  necessarily  changes  to  a 
considerable  extent  the  character  of  the  subsequent  mental  life. 
Such  loss,  however,  is  regularly  compensated  for,  to  some  extent, 
by  an  increase  of  mental  activity  along  the  lines  which  remain  open 
to  the  mind.  The  man  blind  from  birth  can  never  have  the  same 
course  of  mental  unfolding,  with  respect  to  his  perceptions  of 
things,  his  idea  of  space,  his  feelings  before  the  beautiful,  etc.,  as 
that  open  to  his  more  fortunate  fellow.  But  he  is  not  necessarily 
inferior  in  mental  capacity  and  activity  ;  because  the  development 
of  his  mind,  as  conditioned  upon  the  other  senses,  proceeds  with 
the  ordinary  pace,  although  along  a  different  path. 

The  mind  is  absolutely  dependent  upon  the  nervous  organism  for 
its  awakening  and  furnishing  in  the  life  of  conscious  sensation. 
The  case  of  Laura  Bridgman,  and  others  similar,  show  how  large 
mental  development  is  possible  with  even  a  greatly  diminished  out- 
fit of  the  senses.  But,  of  course,  if  touch  and  muscular  sensation, 
as  well  as  smell,  taste,  hearing,  and  sight,  were  lacking,  no  con- 


.    EELATION   OF  THE   FACULTIES.  625 

scious  mental  life  would  be  possible  in  any  form  known  to  human 
experience.  The  form  in  which  the  sensations  shall  combine,  and 
the  time-order  of  their  recurrence,  are  also  dependent  upon  the 
character,  number,  and  succession  of  the  cerebral  excitations 
caused  by  external  or  internal  stimuli.  But  when  once  the  mind 
is  started  upon  its  career  of  unfolding  its  powers,  it  maintains  a 
relative  independence  of  its  physical  basis.  Not  that  sensations  and 
resulting  presentations  of  sense,  together  with  the  reproduced  im- 
ages of  such  mental  products,  do  not  always  continue  to  furnish 
indispensable  factors  and  conditions  of  all  mental  development. 
In  the  most  abstract  thought,  and  in  the  highest  flights  of  the  im- 
agination, the  mind  never  wholly  gets  away  from  the  world  of  sen- 
sation and  perception,  with  its  immediate  dependence  upon  the 
activities  of  the  physical  and  nervous  basis.  On  the  other  hand, 
the  course  and  extent  of  its  unfolding  are  such  as  to  show  that  its 
stages  and  laws  do  not  all  correspond  to  those  which  characterize 
the  evolution  of  this  basis.  Its  general  dependence  upon  such 
basis,  in  all  its  development,  is  through  the  sensations  and  their 
reproduced  images. 

§  11.  Several  references  to  the  second  argument  (comp.  §  3)  for 
our  view  of  tlie  development  of  mind  have  ah-eady  been  made.  This 
argument  is  based  upon  the  fact  that  certain  indispensable  elements 
enter  into  the  development  of  mind  which  have  nothing  similar  to 
them,  or  strictly  correlated  with  them,  in  the  evolution  of  the  ma- 
terial mechanism.  The  mind  can,  indeed,  undergo  no  development 
except  as  conditioned  upon  these  elements.  But  the  elements 
themselves  cannot  be  regarded  as  the  expression  in  consciousness 
of  merely  physical  causes,  or  as  flowing  necessarily  from  more 
primitive  activities  of  the  mind  which  may  possibly  be  regarded  as 
the  expression  of  such  causes. 

All  three  of  those  fundamental  forms  of  activity  which  are  recog- 
nized in  the  ordinary  threefold  division  of  the  soul  into  faculties — 
namely,  acts  of  feeling,  acts  of  knowledge,  and  acts  of  will — neces- 
sarily enter  into  the  development  of  the  mind.  Its  development 
consists  in  the  unfolding  of  these  three  classes  of  acts,  in  their 
mutual  dependence  and  according  to  the  laws  which  belong  to  each. 
Among  each  of  these  three  great  classes  of  acts  there  are  certain 
subordinate  kinds  that  defy  all  attempts  whatever  to  correlate  them 
with  the  changes  in  the  nervous  mechanism,  or  to  explain  them  as 
necessarily  or  actually  arising  out  of  such  physical  changes.  Such 
are  the  feeling  of  moral  obligation,  the  sentiment  of  justice,  the 
love  of  truth,  and  certain  of  the  higher  aesthetic  feelings.  Among 
the  acts  of  knowledge,  such  are  the  mind's  relating  activity,  its  use 
40 


626  PSYCHICAL   FACTOKS   SUPREME. 

of  the  principle  of  reason  and  consequent  in  drawing  deductions, 
its  confident  assumption  that  similar  phenomena  are  signs  of  like 
realities,  and  that  the  world  of  sensuous  individual  experience  is 
but  the  manifestation  of  an  invisible  world  of  real  beings,  with  per- 
manent properties  and  forces,  acting  and  reacting  under  law. 
Such,  also,  are  the  acts  of  deliberate  choice  among  courses  of  con- 
duct, under  the  influence  of  moral  considerations — the  acts  of  "free 
will "  in  the  highest  sense  of  the  term. 

Not  one  of  the  higher  acts  of  feeling,  knowing,  or  willing,  so  far 
as  its  sui  generis  character  is  concerned,  admits  of  being  correlated 
with,  or  represented  under,  any  of  the  conceivable  modes  of  the 
motion  and  relation  of  molecules  of  nervous  substance.  Certain 
sensations  and  perceptions  connected  with  the  rise  and  growth  of 
the  higher  forms  of  feeling  have,  undoubtedly,  a  physical  basis  ; 
but  such  basis  is  not  assignable  to  the  feelings  themselves.  Sen- 
sations and  perceptions,  which  are  resultants  (in  some  meaning  of 
the  word)  of  physical  processes,  are  discriminated  by  judgment  and 
made  the  basis  of  deductions  and  inductions.  But  admitting  this 
does  not  one  whit  the  better  enable  us  to  conceive  of  a  physical 
process  which  can  account  for  the  sui  generis  character  of  the  re-" 
lating  activity  itself.  Acts  of  "  free  will,"  so  called,  always  take 
place  under  certain  conditions  of  sensation  and  perceiDtion,  as  well 
as  of  desire ;  but  the  physical  correlates  of  these  conditions  can  in 
no  respect  be  conceived  of  as  being  also  correlates  of  the  conviction 
that  the  choice  is  responsible  and  free. 

Now,  if  such  activities  as  the  foregoing  do  actually  constitute 
indispensable  elements  of  mental  development — and  it  is  obvious 
that  they  do — this  development  cannot  properly  be  accounted  for 
by  assigning  it  to  a  mass  of  nervous  matter  undergoing  a  physical 
process  of  evolution,  after  the  manner  of  the  growing  human  brain. 
Such  development  rather  implies  a  real  being  of  another  than  the 
physical  order.  This  being  must  be  thought  of  as  stimulated  by 
the  rise  and  recurrence  of  sensations  and  images  of  past  sensations, 
to  unfold  its  own  activities  as  conditioned  by  its  own  inherent 
powers.  Like  every  other  real  being,  the  history  of  its  unfolding 
is  dependent  upon  the  relations  in  which  it  is  placed  to  other  real 
beings  ;  but  it  is  nevertheless  a  history  determined  also  by  what 
the  being  is. 

§  12.  The  trial  will  doubtless  be  made  to  escape  from  the  con- 
clusions hitherto  reached,  by  means  of  help  derived  from  a  certain 
psychological  theory  of  the  development  of  mind.  It  may  be  ad- 
mitted that  the  attempt  to  find,  directly,  an  adequate  phj^sical  basis 
for  all  these  so-called  higher  faculties,  or  modes  of  the  behavior  of 


'  MECHANICAL  THEORY  OF  MIND.  627 

the  mind  in  its  development,  must  be  abandoned.  But  the  higher 
faculties  themselves — it  is  said — are  to  be  regarded  as  develop- 
ments of  the  simplest  activities.  These  highest  faculties  of  all  may 
then  be  directly  connected  with  the  evolution  of  the  body,,  or  of 
the  cranial  mass,  through  the  simplest  mental  activities.  In  this 
way  a  kind  of  necessitated  psychical  mechanism  is  set  up,  which  is 
itself  entirely  explicable  as  a  development  from  one  kind  of  element 
(the  sensation) ;  and  then,  by  regarding  this  one  kind  of  element 
as  connected  with  the  motion  of  nervous  molecules  in  a  purely 
mechanical  way,  the  need  is  obviated  of  supposing  any  real  being 
called  Mind  as  undergoing  a  process  of  mental  development. 

For  example,  it  may  be  claimed  that  the  one  simple  and  undif- 
ferentiated element  of  all  psychical  experience  is  the  "neroous 
shock."  This  nervous  shock  is  merely  the  simplest  expression  or 
result  in  consciousness  of  a  nerve  commotion  set  up  by  the  action 
on  the  nervous  mechanism  of  external  or  internal  stimulus.  By 
differentiation  and  combination  of  the  nervous  shocks,  the  so-called 
simple  sensations  arise.  By  reproduction  of  similar  combinations 
of  fainter  shocks,  the  images  of  memory  are  produced.  By  "  ag- 
glutination "  and  "  agglomeration  "  of  the  sensations  and  ideas, 
judgments  take  place — only,  since  some  new  kind  of  idea  does  cer- 
tainly seem  to  be  involved  in  the  essence  of  judgment,  it  must  be 
held  that  a  "  feeling  of  relation  "  is  somehow  slipped  in  between  the 
agglutinated  and  agglomerated  sensations  and  ideas.  By  still  more 
elaborate  groupings  of  the  simple  ideas,  systems  of  thought  and  so- 
called  ideas  of  the  highest  order  of  abstraction — like  the  ideas  of 
space,  time,  etc. — come  into  mental  being. 

In  the  foregoing  way,  all  the  so-called  mental  processes  that  con- 
stitute the  development  of  the  mind  are  strictly  correlated,  under 
laws  analogous  to  those  which  control  the  relations  of  physical  ele- 
ments, with  the  processes  that  go  on  in  the  nervous  system  ;  thus 
so-called  "  psychology  "  results  in  bringing  the  mind  of  man  into 
the  same  strict  subjection  to  the  energy  of  outside  nature,  under 
the  law  of  the  conservation  and  correlation  of  energ}'^,  that  charac- 
terizes all  the  phenomena  with  which  modern  physical  science  is 
accustomed  to  deal. 

The  above-mentioned  theory  is  doubtless  admirably  simple  and 
thorough-going.  But  its  somewhat  extreme  simplicity  and  thor- 
oughness constitute  very  important  objections  to  it.  In  so  crude  a 
form  it  scarcely  deserves  detailed  consideration.  It  is  enough  in 
this  connection  to  call  attention  to  the  fact  that  the  theory  is  built 
throughout  upon  unverified  assumptions ;  and  that,  even  granting 
its  assumptions,  it  affords  no  adequate  description  whatever  of  the 


628  PSYCHICAL    FACTORS    SUPUEME. 

real  process  of  human  mental  development.  No  theory  of  nerve- 
commotion  has  yet  been  devised  to  connect  it  with  the  externa] 
stimuli  under  the  law  of  the  conservation  of  energy.  If  by  "  ner- 
vous shock  "  be  meant  a  psychical  event,  the  break  between  such 
shock  and  the  nerve-commotion  which  is  its  antecedent  is  absolutely 
impassable  ;  no  physical  energy,  under  the  general  law  of  its  con- 
servation and  correlation,  can  pass  this  break. 

Moreover,  there  is  no  actual  or  conceivable  psychical  event  cor- 
I'esponding  to  the  undifferentiated  nervous  shock.  Sensations  are 
always,  as  such,  and  from  their  very  nature,  of  this  or  that  definite 
quality.  An  undifferentiated  psychical  element  is  a  pure  abstrac- 
tion. Nor  do  sensations  and  their  remembered  images  constitute 
such  existences  that  they  can  be  spoken  of  as  "  agglutinated  "  or 
"  agglomerated."  The  so-called  "  feelings  of  relation,"  slipped  in 
between  the  single  ideas  and  sensations,  if  by  this  be  meant  any- 
thing less  than  relating  activities  of  the  mind,  are  absurdities  in  no 
way  fitted  to  explain  or  represent  the  act  of  judgment.  And,  finally, 
this  entire  account  of  the  course  of  mental  evolution  is  an  utterly 
inadequate  description  of  what  actually  takes  place  in  the  history 
of  even  the  poorest  and  weakest  human  minds. 

§  13.  All  theoi'ies  of  the  mental  development  which  account  for 
the  different  so-called  faculties  and  stages  of  the  growth  of  mind  as 
■  though  they  flowed  necessarily  from  some  one  fundamental  activity 
are  inadequate  and  misleading.  The  mind  is  indeed  a  unit-being, 
but  its  unity  is  not  of  the  kind  alleged  by  these  theories.  Its  dif- 
ferent constitutional  modes  of  behavior  are  not  to  be  resolved  into 
each  other,  or  into  any  one  most  primitive  activity  ;  nor  do  they  all 
necessarily  flow  forth  from  such  a  primitive  activity.  They  manifest 
the  rich  variety  of  the  mind's  nature.  They  do,  indeed,  preserve  a 
certain  order  in  time  with  regard  to  the  relative  amount  of  their 
unfolding.  The  different  periods  of  life  are  characterized  by  dif- 
ferent stages  of  mental  development ;  these  different  stages  of  men- 
tal development  are  characterized  by  a  relative  jDrominence  of  partic- 
ular faculties,  or  modes  of  the  behavior  of  the  mind.  But  because 
such  a  time-order  is  followed  in  the  development  of  the  mind,  we 
can  by  no  means  conclude  that  the  faculties  latest  develojDed  are 
any  the  less  native  and  essential  to  the  character  of  the  mind.  Nor 
is  it  true  that  these  latest  and  highest  faculties  can  be  explained  as 
mere  developments  from,  or  modifications  of,  the  earlier  and  sim- 
pler. 

Strictly  speaking,  none  of  the  faculties,  or  constitutional  modes 
of  the  behavior  of  the  mind,  admit  of  being  explained  as  mere  de- 
velopments of  other  faculties.     This  is  true  even  of  those  minor 


NO   DEDUCTION   OF   FACULTIES.  629 

forms  of  activity  which  it  is  customary  to  class  under  the  same  fac- 
ulty. That  I  have  the  sensation  "  red  "  is  no  reason  why  I  should 
have  the  sensation  "  green  ;  "  and  that  I  have  the  sensations  "red  " 
and  "green"  is  no  reason  why  I  should  also  have  the  sensation 
"  blue."  Neither  does  the  existence  of  all  these  so-called  funda- 
mental color-tones,  of  itself,  form  any  reason  why  the  mind  should 
be  affected  with  any  of  all  the  thousands  of  sensations  supposed  to 
be  compounded  from  them.  None  of  these  color-tones,  psychologi- 
cally considered,  can  be  regarded  as  a  development  from  the  fun- 
damental color-tones.  That  I  am  affected  with  a  certain  sensation 
of  color,  lying  at  the  bottom  of  the  spectrum's  scale,  when  several 
billion  vibrations  of  ether  strike  the  retina,  and  with  a  qualitatively 
different  sensation  when  the  number  of  vibrations  is  increased  by 
several  billions  more,  cannot  be  explained  as  an  evolution.  The 
same  remark  holds  within  the  Hmits  of  each  of  the  other  senses. 
Their  scales  of  quality  are  not  such  that  experiences  at  one  place 
of  the  scale  can  be  evolved  from  those  at  other  places  of  the  scale. 
Some  of  them,  such  as  smell  and  taste,  do  not  admit  of  being  re- 
ferred to  any  form  of  a  scale  or  diagram  representing  relations  of 
quality.  The  feeling  of  heat  is  not  another  phase  of  the  feeling  of 
cold  ;  neither  of  the  feelings  of  temperature  is  to  be  explained  as 
arising  out  of  feelings  of  pressure  or  motion. 

When  the  sensations  of  the  different  senses  are  compared  with 
each  other,  the  impossibility  of  considering  any  of  the  classes  as 
developing  from  any  other  becomes  yet  more  apparent.  That  a 
sentient  being  has  an  experience  of  hearing  musical  tones  which  rise 
in  pitch  as  the  number  of  acoustic  vibrations  varies  from  thirty  to 
thirty  thousand  is  no  reason  at  all  why  the  same  being  should  have 
an  experience  of  seeing  colors  that  change  their  "  color-tone  "  as  the 
number  of  light-vibi'ations  varies  from  about  four  hundred  billions 
to  about  seven  hundred  billions.  In  the  development  of  the  mind, 
the  senses  may  actually  awaken  in  a  certain  order  more  or  less  defi- 
nitely fixed.  But  this  is  very  different  from  holding  that  the}^  develop 
out  of  each  other,  or  that  they  are  all  developments  of  some  undif- 
ferentiated sense-element,  the  psychical  correlate  of  the  nervous 
shock.  Moreover,  our  percepts,  or  knowledges  of  "  Things,"  cannot 
be  regarded  as  mere  developments  of  sensations.  That  a  sentient 
being  should  have  sensations  of  sound  and  smell  and  taste,  and  even 
of  light,  color,  temperature,  and  pressure,  is  not  of  itself  a  sufficient 
reason  for  its  having  perceptions  such  as  belong  to  human  experi- 
ence. The  only  way  in  which  such  perceptions  can  be  regarded  as 
the  necessary  resultants  of  the  sensations  which  enter  into  them  as 
component  pnrts  is  by  taking  the  nature  of  the  mind  into  the  ac- 


630  PSYCHICAL   FACTOES   SUPREME. 

count.  But  this  implies  that  perceptions  are  not  developed  forms 
of  sensations ;  that  they  are  rather  advanced  forms  of  the  activity 
of  that  real  being  which  is  developing  under  the  experience  of 
sensation — elaborate  products  of  the  synthetic  activity  of  mind. 

§  14.  The  knowledge  of  things  by  perception  involves  the  activ- 
ity of  the  mind  as  memory  and  judgment.  But  acts  of  memory 
and  judgment  are  not  developments  from  perception  ;  they  are 
not  merely  modified  forms  of  sensations  as  recurring  or  combined 
under  the  action  of  physical  antecedents.  All  talk  about  the  "  im- 
age "  of  memory  as  though  it  were  merely  a  faint  or  faded-out  im- 
pression of  sense  is  quite  unavailing  ;  it  does  not  hit  the  real  point 
of  inquiry,  and  consequently  does  nothing  to  explain  the  mystery 
(comp.  Part  11.,  chajD.  X.,  §§  18  ff.).  The  vital  element  in  memory, 
that  which  makes  it  to  be  memory,  is  neither  a  sensation,  nor  a 
modified  form  of  sensation,  nor  a  development  of  sensation.  The 
same  statement  is  true  of  judgment. 

The  relating  activity  of  mind,  the  power  to  bring  two  objects 
together  in  the  \inity  of  consciousness,  and,  while  keeping  their 
ideas  distinctly  separate,  to  bind  them  into  one  under  the  mental 
affirmation  of  their  likeness  or  unlikeness — this  is  a  new  and  start- 
ling mode  of  the  activity  of  mind  as  contrasted  with  merely  being 
affected  in  sensation.  Minimize  it  as  we  may,  we  cannot  look  upon 
this  activity  as  a  mere  "  resultant  "  of  two  sensations  or  images  of 
sensations  arising  simultaneously  in  the  mind.  We  cannot  consider 
judgment  under  the  principle  of  the  conservation  and  correlation  of 
energy.  To  treat  it  as  such  involves  the  grossest  misapplication  of 
the  laws  which  control  the  coincidence  or  conflict  of  physical  forces. 
Nor  are  the  different  forms  of  the  relating  activity  of  the  mind — 
concept,  judgment,  deduction,  induction — to  be  legarded,  strictly 
speaking,  as  developments  from  each  other  or  from  any  one  mental 
activity  simpler  than  any  of  them.  They  may  all,  indeed,  be  consid- 
ered as  modes  of  the  relating  activity,  because  they  involve  discrim- 
ination, the  discernment  of  likenesses  and  unlikenesses.  Bat  each 
one  of  them  involves  somewhat  more  than  simjDle  discrimination  ; 
each  one  involves  other  elements  peculiar  to  itself.  That  a  sentient 
being  should  simply  judge,  or  affirm  this  of  that,  is  not  of  itself  a 
sufficient  reason  why  it  should  also  make  inferences  by  syllogistic 
processes  or  arrive  at  general  laws  by  induction.  Indeed,  the 
former  may  belong  to  many  animals  which  are  incapable  of  the 
latter. 

§  15.  We  may  proj)erly  continue  the  foregoing  line  of  remarks  into 
the  consideration  of  the  mind's  most  general  activities.  Modern 
losychology,  we  have  seen,  is  accustomed  to  distinguish  faculties  of 


UNITED   ACTION   OF   FACULTIES.  631 

knowing,  feeling,  and  willing  as  belonging  to  the  mind.  But  it  is 
emphatically  ti-ue  that  no  one  of  these  three  faculties  can  be 
i-egarded  as  developed  from  any  other  one,  or  from  any  two  com- 
bined. That  a  being  feels — that  is,  is  affected  with  a  state  of 
consciousness  more  or  less  pleasurable  or  painful,  and  having  a 
characteristic  quality — is  in  itself  no  ground  for  explanation  of  its 
knowing  '•  Tuings"  through  sense-perception,  and  inference.  Con- 
versely, a  being  is  conceivable  with  the  knowledge  of  an  archangel, 
but  without  experience  of  desire,  emotion,  or  sentiment  of  attrac- 
tion or  rej)ulsion.  Sucli  a  being  would  indeed  have  to  attain  its 
knowledge  in  other  ways  than  those  open  to  us,  and  we  find  it 
difficult  or  impossible  to  imagine  precisely  what  such  knowledge 
could  be  like.  But  growth  in  knowledge  is  a  different  thing  from 
the  unfolding  of  mere  feeling  ;  and  the  former  cannot  be  explained 
as  arising  out  of  the  latter.  Acts  of  will  are,  indeed,  always  actually 
dependent  upon  knowledge  and  feeling,  and  cannot  even  be  con- 
ceived of  as  taking  place  without  this  dependence.  But  acts  of 
will  are  not  mere  developments  of  those  acts  of  knowledge  and 
feeling  on  which  they  undoubtedly  depend.  The  act  of  choice  in- 
volves a  new  element,  an  element  not  to  be  necessarily  evolved  from 
the  other  activities  of  mind. 

§  16.  We  are  so  accustomed  to  the  action  in  common,  in  the 
unity  of  consciousness,  of  all  the  so-called  faculties,  that  any 
attempt  to  account  for  them  as  different  modifications  of  one  form 
of  energy  meets  with  a  favorable  reception.  Nothing  thus  far  said 
is,  of  course,  to  be  construed  to  the  prejudice  of  the  unity  of  the 
mind.  But,  on  the  other  hand,  the  incomparable  wealth  in  variety 
of  its  natural  achievements  should  not  escape  our  notice.  From 
the  beginning  to  the  end  of  conscious  life,  the  forth-puttings  of  the 
mind  continue.  They  are  all  actual  concrete  events,  happenings  in 
consciousness  which  has-e  no  permanent  existence  and  are  never 
twice  precisely  alike.  That  they  are,  however,  ahke  in  certain 
particulars  and  unlike  in  others,  we  can  observe  in  consciousness 
itself.  Indeed,  it  is  upon  this  fact  that  the  possibility  of  any 
orderly  progress,  any  true  development  of  mind,  depends.  But 
the  different  classes  of  mental  activities  are  not  to  be  regarded  as 
though  they  could  themselves  be  explained  each  from  the  other,  as 
the  different  stages  of  the  embrj'o  of  an  animal  or  of  the  germinat- 
ing and  growing  seed  of  a  plant  are  successively  evolved. 

The  development  of  mind,  therefore,  cannot  be  explained  after 
the  analogy  of  the  accretion  of  molecules  within  a  germ,  and  the 
resulting  division,  multiplication,  and  advancing  arrangement  of 
the  living  cells  into  sepai'ate  organs  of  the  entire  system.     No  real 


632  PSYCHICAL   FACTOES   SUPREME. 

elements  of  the  mind  exist  which  can  aggregate  to  themselves  other 
elements  by  absorbing  them  as  pabulum,  or  can  grow  by  arranging 
the  new  material  thus  gained  according  to  the  energies  inherent  in 
the  material  already  organized.  The  life  of  consciousness  is  a  never- 
ceasing  change  of  states.  Yet  the  result  of  this  change  of  states  is 
an  orderly  history,  a  true  development.  Such  development  is  not 
merely  the  expression  of  the  evolution  of  the  material  basis  of  some 
of  these  mental  states.  For  it  does  not  follow  the  same  order  or 
the  same  laws  as  govern  the  material  evolution ;  and  some  of  its 
most  important  factors  cannot  be  regarded  as  having  any  physical 
correlate,  or  as  evolved  from  other  factors  which  have  such  a  corre- 
late. The  development  of  Mind  can  only  he  regarded  as  the  progres- 
sive manifestation  in  consciousness  of  the  life  of  a  real  being  which, 
although  taking  its  start  and  direction  from  the  action  of  the  physi- 
cal elements  of  the  body,  proceeds  to  unfold  powers  that  are  sui  generis, 
according  to  laws  of  its  own. 


CHAPTER    III. 
EEAL    CONNECTION    OF    BEAIN    AND    MIND. 

§  1.  That  certain  uniform  relations  exist  between  the  mental 
phenomena  and  the  action  of  stimuli  upon  the  nervous  system,  is  a 
most  general  conclusion  of  Physiological  Psychology.  These  rela- 
tions are  chiefly  concerned  with  variations  which  take  place  in  the 
quality,  intensity,  combination,  and  time-order  of  the  states  of  con- 
sciousness, as  dependent  upon  the  varying  amounts  and  order  of 
different  modes  of  physical  energy  as  applied  to  the  end-organs  of 
sense.  But  evidence  enough  exists  to  show  that  the  more  ultimate 
psycho-physical  relations  are  those  which  exist  between  states  of  the 
brain  and  states  of  the  mind.  The  dependence  of  mental  states  on 
physical  events  outside  of  the  body,  or  at  its  periphery,  is  gained  by 
means  of  the  central  organs  of  the  nervous  system.  In  the  case  of 
man,  at  least,  what  happens  be^'ond  the  cerebral  hemispheres  is 
significant  for  the  states  of  consciousness  only  as  the  hemisiDheres 
themselves  are  affected  by  it.  What  happens  heyond  the  cerebral 
hemispheres  becomes  the  cause  or  antecedent  of  what  happens  in 
consciousness,  through  this  portion  of  the  brain.  If  our  informa- 
tion were  sufficient,  then,  the  empirical  science  of  the  connection 
of  body  and  mind  would  comprise  a  statement  of  all  the  relations 
which  exist  between  the  mental  phenomena  and  the  changes  with 
respect  to  chemical  constitution,  structural  form,  and  physiological 
function,  which  take  place  in  the  molecules  of  the  cerebral  areas. 

But  even  if  the  conditions  were  already  fulfilled  for  a  complete 
science  of  Physiological  Psychology,  we  should  scarcely  find  our 
speculative  inquiries  satisfied  by  this  science.  The  desire  would 
doubtless  still  be  strong  to  discover  some  more  general  statement 
for  the  real  connection  between  physical  and  psychical  phenomena. 
The  question  would  still  be  raised :  What,  then,  is  the  one  inclusive 
proposition,  or  word,  or  term,  which  gives  the  essence  of  all  the  re- 
lations between  the  brain  and  the  mind  ?  It  would  seem  tedious  and 
disappointing  to  reply  to  this  question  by  again  enumerating  all  the 
particulars  which  psycho-physical  science  has  discovered.  Let  it  be 
taken  for  granted  that,  when  lesions  happen  in  certain  areas  of  the 


634  MIND   AND   ITS   OEGAN. 

cerebral  cortex,  such  or  such  disturbances  of  the  phenomena  of 
consciousness  take  place  ;  that  when  so  many  molecular  vibrations  of 
a  given  wave-form  and  intensity  occur  within  the  cerebral  elements, 
sensations  of  a  certain  fixed  quality  and  quantity  arise  in  the  mind  ; 
that  when  certain  fainter  vibrations  of  like  wave-form  return  in  the 
same  elements,  reminiscences  of  the  aforesaid  sensations  are  ex- 
perienced, etc.,  etc.  We  are  still  inclined  to  ask  :  What  is  the 
meaning  of  all  this  ?  or,  How  are  brain  and  mind,  actually  and  in 
principle,  related  to  each  other  ? 

It  is  in  deference  to  the  raising  of  inquiries  of  the  foregoing 
rational  sort^ — inquiries  which  are  perpetually  repeated  all  the  way 
along  the  path  of  psychological  research — that  we  speak  further  of 
a  7^eal  connection  between  brain  and  mind.  Of  course  every  such 
form  of  speech  involves  the  assumption  that  the  mind  is  a  real  be- 
ing which  can  stand  in  relation  to  other  real  beings,  and  not 
merely  the  formal  or  grammatical  subject  of  mental  phenomena. 
This  assumption  has  already  been  made  and  partially  verified.  In 
continuing  to  make  it  for  the  purposes  of  the  present  chapter,  we 
shall  find  it  still  further  verified. 

§  2.  Various  attempts  have  been  made,  from  one  or  another 
point  of  view,  to  sum  up  in  some  single  Avord  the  relations  that 
maintain  themselves  between  the  body  and  the  soul.  Thus,  the 
body  has  frequently  been  spoken  of  as  the  "  seat  "  or  "organ  "  of 
the  soul.  Looking  at  these  relations  fi'om  the  more  materialistic 
point  of  view,  we  have  already  seen  how  mental  phenomena  may 
be  regarded  as  the  "  products  "  or  "  resultants  "  or  "manifesta- 
tions "  of  the  functional  activity  of  the  brain.  More  highly  figura- 
tive terms  even  have  often  enough  been  employed.  The  body  has 
been  called  the  "  prison  '"'  or  "  tenement  "  or  "  tabernacle  "  of  the 
soul.  Not  seldom,  also,  has  the  mind  been  represented  as  master- 
ing and  controlling,  and  even  "  moulding  "  the  body — somewhat 
as  the  rider  subdues  and  guides  his  horse,  or  the  worker  in  clay 
and  metal  shapes  the  product  of  his  toil.  One  form  of  the  doctrine 
of  "  Animism  "  has  held  that  the  mind  is  identical  with  the  vital 
principle,  which  is  busy  from  the  very  impregnation  of  the  ovum 
in  shaping  its  increasing  molecules  according  to  an  unconscious  or 
dimly  conscious  plan.  Much  debate  has  also  been  held  as  to 
whether  the  conception  of  "  cause  "  is  applicable  to  any  of  the  rela- 
tions in  which  body  and  soul  stand  to  each  other — whether,  indeed, 
it  must  not  rather  be  held  that  what  happens  in  one  is  only  the 
"  occasion "  on  which  some  underlying  cause,  common  to  both, 
operates  to  pi'oduce  a  change  in  the  other. 

§  3.  The  inquiry  in  what  sense,  if  at  all,  the  brain  can  be  said  to 


BRAIN   AS   THE   SEAT   OF   MIND.  635 

be  the  "  seat "  of  the  mind  is  more  easily  answered  in  a  negative 
than  a  positive  way.  Nothing  but  the  cnidest  notions,  both  of  the 
nervous  mechanism  and  of  the  mind,  would  be  consistent  with  any 
of  the  more  literal  and  direct  interpretations  of  this  word.  Few 
would  seriously  regard  the  mind  as  a  special  entity,  whether  con- 
structed of  ordinary  material  atoms  or  constituted  in  ethereal  form, 
that  maintains  a  sitting  or  other  posture  amidst  the  cerebral  masses. 
Nor  is  it  any  more  correctly  conceived  of  as  thinly  diffused  over 
the  entire  mechanism  of  nerve- cells  and  nerve-fibres,  or  as  wander- 
ing about  among  the  nerve -molecules  to  find  its  temporary  "  seat  " 
where  occasion  seems  to  require  its  presence.  And,  although  some 
of  the  phenomena  of  mind  and  brain  perhaps  admit  very  well  of 
being  brought  under  the  conception  of  the  atom,  acting  and  acted 
upon  in  varying  relations  to  other  atoms  of  kinds  different  from 
itself,  no  essential  gain  is  made  by  the  attempt  to  regard  the  mind 
as  in  reality  an  atom.  In  brief,  there  is  no  literal  meaning  of  the 
words  in  which  we  can  speak  of  the  mind  as  seated  in  the  brain. 
The  phrase,  the  brain  is  the  "  seat  "  of  the  mind,  is,  hoAvever,  very 
well  adapted  to  raise  the  whole  question  of  the  spatial  qualities  of 
the  mind,  and  of  its  alleged  spatial  relations  to  the  molecules  of 
the  central  nervous  system.  We  shall,  then,  briefly  consider  the 
question  in  this  form. 

§  4.  There  can  be  no  doubt  that  ordinary  language  justifies  us  in 
speaking  of  the  soul  as  in  the  body,  in  some  sense  in  which  this 
term  does  not  apply  to  any  other  collection  of  material  atoms. 
The  human  soul  is  in  the  human  body  as  it  is  not  in  the  bird,  the 
tree,  the  house,  the  star.  Even  that  waj'  of  regarding  the  mind's 
nature  which  does  not  hesitate  to  speak  as  though  it  were  a  thinly 
diffused  and  half-spiritualized  form  of  matter,  assents  to  the  neces- 
sity of  asserting  a  special  relation  in  space  between  it  and  the  body. 
Hence  some  old-time  philosophies  represented  the  soul  in  percep- 
tion as  streaming  out  through  the  avenues  of  sense  in  order  to  get 
the  sensuous  object  into  its  embrace  :  or  else  pictured  some  ethe- 
realized  copy  of  this  object  as  streaming  into  the  soul  by  the  same 
avenues.  But  even  such  a  view  of  the  nature  and  activities  of  the 
mind  is  based  upon  the  claim  that  the  body  is,  in  some  sort,  the 
peculiar  dwelling-place,  or  "seat,"  of  the  mind.  A  correct  account 
of  the  process  by  which  the  world  of  things  becomes  known  shows 
that  all  our  experience  is  connected  with  the  establishing  and  jus- 
tifying of  this  claim.  There  are  no  "  things "  known  to  experi- 
ence except  as  our  sensations,  or  modes  of  being  affected,  are  both 
localized  and  projected  ej;^ra-mentally.  Inducements  and  consid- 
erations, such  as  have  already  been  treated  in  great  detail  (Part  II., 


636  MIND   AND   ITS   ORGAN. 

chaps.  VI.  and  VII.)  irresistibly  urge  the  mind  to  arrange  all  its 
phenomena  into  two  great  classes — phenomena  which  are  quaUties 
of  outside  things,  and  phenomena  which  are  mere  states  of  internal 
experience.  But  the  same  inducements  and  considerations  compel 
us  to  look  upon  certain  phenomena  of  the  first  class  as  related  to 
our  mere  states  of  consciousness  in  a  peculiar  way.  The  world  of 
things  outside  always  (at  least  in  ordinary  experience)  affects  us — 
is  perceived  by  us  or  modifies  our  consciousness — through  the  body. 
The  mind  is,  therefore,  said  to  be  in  the  body. 

The  conclusion  from  the  foregoing  general  experience  is  con- 
firmed by  certain  experiences  of  a  special  order.  The  feeUngs  of 
pleasure  and  pain,  which  have  so  immediate  and  incontestable  a 
value  for  the  life  of  the  mind,  are  all  connected  with  sensations 
more  or  less  definitely  localized  in  the  body.  Hence  men  say,  "My 
nose  is  ofiended  by  this  smell,"  "My  tooth  is  aching,"  or  "My 
limb  is  suffering."  So  close  is  the  connection  between  the  localized 
sensations  and  the  painful  or  pleasurable  states  of  the  mind,  that 
the  mind  actually  seems  to  be  suffering  in  that  part  of  the  body 

■where  the  sensations  are  localized.     When  the  localizino;  of  sensa- 

•  .  ... 

tions  connected  with  feelings  of  strong  "tone"  is  very  indefinite, 

as  it  is  in  cases  where  the  feelings  arise  from  the  condition  of  large 
areas  of  the  internal  organs,  the  soul  seems  to  be  suffering  in,  and 
throughout,  almost  the  entire  body. 

Furthermore,  both  ordinary  experience  and  scientific  observation 
require  us  to  regard  the  mind  as  standing  under  certain  special  re- 
lations to  parts  of  the  body.  The  ancients  located  the  soul  in  the 
heart  or  lower  viscera,  because  of  certain  marked  connections  be- 
tween the  states  of  the  soid  and  the  condition  of  these  organs. 
But  to  speak  of  the  soul  as  seated  in  the  heart  or  other  viscera 
plainly  applies  most  pertinently  only  to  the  soul  as  an  emotional 
being  ;  the  obvious  connection  of  the  head  with  most  of  the  more 
obtrusive  sensations  tends  to  confirm  us  in  the  belief  that  the 
mind,  as  perceptive,  has  its  "seat"  in  that  region  of  the  body. 
For  reasons  already  given  in  detail  (see  Book  II.,  chaps  I.  and  IE. 
and  elsewhere),  modern  scientific  researches  justify  us  in  narrowing 
more  precisely  the  local  domain  within  which  we  can  affirm  the 
mind  to  have  its  seat.  The  mind  is  certainly  in  the  nervous  sys- 
tem, in  a  sense  in  which  it  is  not  in  any  otlier  of  the  systems  of  the 
animal  bod}'.  More  precisely  yet,  it  is  pre-eminently  in  the  brain  ; 
and,  among  all  the  complex  groups  of  encephalic  organs,  the  final 
and  special  claim  of  the  cerebral  cortex  to  be  the  "  seat "  of  the 
mind  is  most  easily  maintained.  Here,  in  this  convoluted  rind 
which  forms  the  interlaced  "  projection-systems  "  of  sensory  and 


NO   MATEEIAL   SEAT   OF   MIND.  637 

voluntary  motor-impiilses,  here — if  anywhere — must  it  be  held 
that  the  subject  of  the  states  of  consciousness  has  its  dwelling- 
place  and  home. 

§  5.  At  this  point,  however,  the  results  of  modern  scientific  in- 
quiry become  unfavorable  to  the  effort  yet  more  particularly  to 
designate  a  material  "  seat  "  for  the  mind.  The  eager  imagination 
having,  as  it  were,  hunted  the  soul  down  as  it  retreats  inward  and 
upward  to  the  higher  regions  of  the  supreme  central  organs,  re- 
quires some  more  precise  information  as  to  just  where  in  these 
regions  its  existence  may  be  pointed  out.  Is  there  any  one  mathe- 
matical point,  or  minute  area  in  the  cerebral  cortex  that  is  most 
especially  of  all  the  dwelling-place  of  mind  ?  If  so,  might  it  not 
be  properly  conceived  of  as  ordinarily  remaining  at  this  point  to 
receive  the  messages  despatched  to  it  from  the  various  parts  of  the 
periphery  ;  and  as  executing  its  will  over  those  peripheral  jiarts 
by  sending  back  to  them  corresponding  messages  despatched  from 
the  same  central  point  ?  The  pineal  gland  has  undoubtedly  lost 
the  significance  which  Descartes  gave  to  it  as  the  special  seat  of  the 
soul.  But  can  no  substitute  be  found  to  take  and  hold  so  impor- 
tant a  place  ?  The  answer  of  cerebral  histology  and  physiology  to 
the  foregoing  questions  is,  on  the  whole,  a  decided  negative  (comp. 
Book  I.,  chap.  II.,  and  Book  II.,  chaps.  I.  and  II.). 

Certain  areas  of  the  cerebral  cortex  do,  indeed,  appear  to  have  a 
particular  connection  with  the  execution  of  certain  functions  of  the 
mind  ;  the  exact  nature  of  this  connection,  howevei",  cannot  as  yet 
be  clearly  indicated.  But  the  very  phenomena  on  which  reliance 
is  placed  for  establishing  the  foregoing  connection,  forbid  us  to 
regai'd  the  mind,  in  its  special  relations  to  the  brain,  as  hmited  to 
any  point  or  small  area  of  the  cerebral  cortex.  Considerable  parts 
of  all  the  cerebral  areas  can  be  destroyed  without  impairment  of 
any  of  the  essential  functions  or  faculties  of  mind.  Moreover,  both 
gross  and  microscopic  anatomy  show  us  that  the  cortical  part  of 
the  brain,  like  all  its  other  parts,  is  not  constructed  on  the  plan  of 
having  its  uses  for  the  mind  concentrated  in  any  one  minute  cir- 
cumscribed spot.  In  any  sense  in  which  the  mind  can  be  said  to 
have  its  "  seat "  in  the  brain  at  all,  in  that  same  sense,  and  with 
equal  propriety,  may  the  entire  cerebral  cortex,  Avith  its  vast  com- 
plexity of  nerve-fibres  and  nerve-cells,  be  said  to  be  the  "seat"  of 
the  mind. 

§  6.  And  now  the  puzzling  question  recurs  :  What  that  is  intelli- 
gible can  be  meant  by  designating  the  supreme  central  organs  of 
man's  nervous  mechanism  as  the  "  seat  "  of  his  conscious  mind? 
No  one  is  directly  conscious  of  these  organs.     The  subject  of  con* 


638  MIN^D   AND   ITS   OEGA]^. 

sciousness  is  not  a  beiDg  which  can  be  conceived  of  as  "  posturing  * 
within  or  amongst  a  certain  larger  or  smaller  group  of  materia] 
molecules.  And  yet,  plainly,  in  some  sense  the  mind  is  to  be 
thought  of  as  in  the  brain,  as  it  is  not  in  any  object  outside  of  the 
body,  or  in  any  of  the  non-nervous  organs  of  the  body  (bones,  hair, 
nails,  fat,  muscular  tissue  as  such,  etc.),  or  even  in  the  remainder 
of  the  nervous  system. 

The  only  solution  for  such  a  puzzle  as  the  foregoing — if  solution 
''t  can  be  called — must  always  consist  in  calling  attention  anew  to 
\he  essential  facts  of  the  case.  Certain  particles  of  very  highly 
organized  chemical  constitution,  when  grouped  into  nerve-fibres 
and  nerve-cells,  and  when  further  associated  into  organs,  may  be 
acted  upon  by  appropriate  stimuli.  These  material  particles  are 
locally  in  the  cranial  cavity,  and,  more  precisely,  in  this  or  that  area 
or  organ  of  the  cranial  contents.  Moreover,  a  large  and  important 
part  of  the  phenomena  of  consciousness  consists  in  localized  bodily 
sensations  of  a  painful  or  pleasurable  character.  To  these  facts  in- 
vestigation adds  the  inference  as  based  upon  experiment  and  ob- 
servation in  the  case  of  others,  that  the  localized  sensations  are 
themselves  ultimately  dependent  upon  the  behavior  of  the  afore- 
said material  molecules  in  the  brain.  That  is  to  say,  we  directly 
localize  many  of  our  mental  affections  in  this  or  that  part  of  the 
body  ;  by  remote  pi'ocesses  of  observation  and  argument  we  infer 
that  the  last  material  antecedent  of  them  all  is  the  behavior  of  cei*- 
tain  invisible  parts  of  the  body  within  the  brain.  Therefore  we  say  : 
The  mind  is  in  the  brain  ;  or  the  seat  of  the  mind  is  the  brain.  By 
this,  nothing  further  can  be  meant  of  an  assured  or  intelligible 
character  than  the  emphatic  repetition  of  the  same  principal  facts ; 
the  sensations  which  we  localize  at  the  periphery  of  the  body,  or 
project  from  the  body  in  space,  all  have  a  sui  generis  connection 
with  the  condition  and  action  of  that  portion  of  the  same  body 
which  is  contained  in  the  cranial  cavity.  Our  modes  of  being  af- 
fected are  directly  localized  in  space  outside  of  the  body,  or  in  the 
various  peripheral  parts  of  the  body.  The  part  of  the  body  on 
which  the  activity  of  having  these  percepts  is  immediately  depend- 
ent is  localized  by  science  in  the  brain.  Other  activities  of  mind 
are  probably  also  thus  dependent  on  the  brain.  In  no  other  sense 
can  the  brain  be  said  to  be  the  seat  of  the  mind. 

As  to  the  possibility  of  such  a  sui  generis  relation  between 
material  elements  which  exist  in  space,  and  the  localizing  and  other 
activities  of  a  being  not  to  be  conceived  of  as,  strictly  speaking,  in 
space,  only  experience  is  entitled  to  pronounce.  Such  a  relation  ia 
an  accomplished  fact.     The  fact  is  not  to  be  disputed  on  any  so- 


•     MYSTERY   OF   THE   EELATION.  639 

called  a  priori  gi'ounds  whatever.  Both  the  dicta  which  have  some- 
times been  made  to  bear  on  the  case  are  alike  inapplicable.  On 
the  one  hand,  it  has  sometimes  been  claimed  that  a  being  cannot 
act  where  it  is  ;  on  the  other  hand,  that  a  being  cannot  act  where 
it  is  not.  Nothing,  however,  can  be  known  as  to  how  and  where 
beings  can  or  cannot  act,  except  through  experience  of  how  they 
actually  do  act.  Building  our  conceptions  iipon  the  basis  of  facts, 
we  should  be  inclined  to  say  that  beings  act  upon,  and  are  acted 
upon  by  each  other,  according  to  their  differences  in  constitution 
and  relations  in  space.  Gravitation  keeps  constantly  before  us  the 
example  of  all  bodies  acting  unceasingly  upon  each  other,  in  many 
cases  over  distances  that  are  immense.  Tlie  amount  of  this  action 
depends,  indeed,  upon  the  distance  over  which  it  takes  place  ;  but 
the  action  at  all  is  an  instance  of  beings  acting  where  they  are  not. 

When  material  molecules  are  approached  nearer  to  each  other 
than  a  given  small  distance  we  at  once  discover  new  modes  of  be- 
havior set  up,  which  depend  upon  what  the  molecules  are,  and 
what  their  condition,  etc.  New  laws,  such  as  those  of  cohesion  and 
chemical  affinity,  have  now  to  be  taken  into  the  account.  But 
gravitation,  cohesion,  and  chemical  affinity  are  all  alike  to  be  under- 
stood as  expressive  simjDly  of  the  regular  modes  of  the  behavior  of 
material  elements,  with  reference  to  each  other,  under  varying  con- 
ditions. All  these  modes  of  behavior  modern  physical  science  re- 
duces to  motions  of  various  kinds,  directions,  durations,  and  veloci- 
ties. What  is  true  of  all  material  elements  is  true  of  those  of  the 
brain  ;  they  can  do  nothing  but  move. 

If,  then,  we  are  to  speak  of  the  mind  as  having  its  "  seat"  in  the 
brain,  in  a  literal  way,  we  must  regard  it  as  one  among  the  many 
molecules  or  atoms  of  which  the  brain  is  composed — wandering 
(that  is,  moving  in  a  peculiar  fashion)  among  the  others,  and  so 
variously  acting  on  them,  and  being  acted  upon  by  them.  But  if 
the  mind  were  such  a  molecule  or  atom,  the  only  affection  it  could 
receive  from  the  rest  of  the  brain-molecules  would  be  to  change 
the  kind  and  direction  of  its  own  motion  ;  the  only  effect  the 
mind-atom  could  produce  in  the  material  atoms  of  the  brain  would 
be  to  modify  their  motion  with  respect  to  kind  and  direction.  But 
it  would  still  be  just  as  difficult  as  before  to  understand  how  the 
phenomena  of  consciousness  should  result  from  the  movement  of 
one  atom  among  other  atoms — no  matter  how  peculiar  in  constitu- 
tion each  of  these  two  kinds  of  atoms  (the  mind-atom  and  the 
brain-atoms)  might  be. 

It  does  not  follow,  however,  that  the  relation  of  the  mind  to  the 
brain  is  any  more  ultimately  mysterious  than  that  of  the  molecules 


640  MIND   AND   ITS   ORGAN. 

of  tlie  brain  to  one  another.  Nor  does  it  form  an  insuperable  ob- 
jection to  the  former  relation  that  it  is  not,  like  the  latter,  a  rela- 
tion of  changes  of  position  in  space.  For  who  shall  undertake  to 
affirm  that  beings  which  are  not  extended  and  movable  in  space, 
because  their  very  nature  is  of  another  order,  cannot  exist  in  rela- 
tions of  any  kind  to  beings  which  are  thus  extended  and  movable  ? 
If  the  existence  of  the  former  kind  of  beings  consists  essentially  in 
states  of  consciousness,  this  fact  does  not  prevent  their  dependence 
upon  the  changing  relations  in  space  of  extended  and  movable  be- 
ings. It  is,  in  reality,  in  this  way  that  the  mind  is  related  to  the 
brain.  To  speak  of  the  mind  as  having  its  "seat"  in  the  brain  is 
to  reaffirm  the  reality  of  such  relations. 

§  7.  The  term  "organ  "  (or  instrument)  of  the  mind,  as  applied 
to  the  body,  is  particularly  calculated  to  emphasize  the  relation  of 
the  ideas  and  volitions  which  arise  in  consciousness  to  the  control 
of  the  muscular  apparatus.  But  the  same  term  may  also  be  used, 
though  with  less  of  propriety,  to  describe  the  relation  of  the  brain 
to  the  mind  in  sensation  and  thought.  Thus  we  may  be  said  to 
feel  or  think  with  the  brain,  in  some  manner  supposed  to  be  anal- 
ogous to  that  in  which  the  workman  accomplishes  his  task  by 
availing  himself  of  a  particular  tool  or  instrument.  It  is  obvious, 
however,  that  the  figure  of  speech  suggested  by  these  terms  also 
will  not  admit  of  a  literal  interpretation.  We  cannot  conceive  of 
the  mind  as  a  peculiar  kind  of  material  entity  which,  when  it  de- 
sires or  wills  to  move  the  bodily  members  in  a  certain  way,  lays 
a  clutch — as  it  were — upon  the  nervous  substance  of  the  central 
organs,  and  so  makes  the  body  serve  as  an  "organ"  of  the  desire  or 
volition.  Even  less  are  we  to  conceive  of  the  brain  as  a  complex 
tool  or  mechanism  which  the  mind  uses  in  thought  and  feeling, 
somewhat  as  senses  and  fingers  avail  themselves  of  a  calculating 
machine  or  of  a  musical  instrument. 

In  producing  changes  of  shape  and  position  in  masses  of  matter 
outside  of  our  own  bodies,  we  ordinarily  find  it  convenient  to  use 
some  material  medium  between  those  masses  and  the  various  mov- 
able parts  of  our  own  bodies.  We  throw  up  the  ground  with  spade 
or  shovel,  cut  down  the  tree  with  an  axe,  feed  ourselves  with  knife 
and  fork,  etc.  We  can,  by  means  of  much  more  complicated 
mechanisms,  accomplish  a  great  variety  of  changes  which  it  would 
be  quite  impossible  to  accomplish  without  such  aid.  On  the  other 
hand,  we  sharpen,  define,  and  multiply  our  sensations  and  percepts 
of  things  in  similar  manner.  The  deaf  man  hears  with  a  trumpet 
or  other  acoustic  contrivance  ;  and  the  scientific  observer  contrives 
an  instrument  for  observing  the  absolutely  simple  tones  as  analyzed 


THE   USES   OF   THE   BEAHST.  641 

out  of  the  composite  clang.  With  the  lenses  of  his  spectacles  the 
man  of  defective  vision  sees  what  would  othei'wise  be  invisible  ; 
and  with  a  prism  the  optician  beholds  the  colors  of  the  spectrum. 
Remote  objects  are  brought  near  with  the  use  of  the  telescope,  and 
very  minute  objects  near  by  are  revealed  by  the  microscope. 

It  is  characteristic  of  all  the  most  skilful  use  of  tools  and  instru- 
ments that  they  come  to  seem  to  the  observer  like  a  part  of  his 
own  bodily  mechanism.  By  feelings  of  "  double  contact "  (see 
Part  II.,  chap.  VI.,  §  31)  the  workman  comes  to  know,  with  the 
chisel,  the  wood  or  metal  which  he  is  carving — just  as  the  blind 
man  seems  to  extend  his  conscious  life  to  the  very  end  of  the  stick 
he  is  accustomed  to  carry.  In  these  cases  the  mental  picture  before 
the  practised  mind  is  not  that  of  the  hand  and  the  way  it  must  be 
moved,  but  of  the  graving  tool  and  the  motion  to  be  imparted  to 
it — as  though  the  instrument  itself  were  immediately  subject  to 
volition. 

§  8.  The  conception  of  an  "  organ  "  or  instrument  may  with  pro- 
priety be  extended  so  as  to  cover  the  relation  which  exists  between 
the  nervous  system  and  the  muscular,  and  between  the  central  and 
the  peripheral  parts  of  the  nervous  system.  Thus  it  may  be  said 
that  the  spinal  cord  and  brain  move  the  limbs  with  the  use  of  the 
afferent  nerves,  or  that  the  cerebral  hemispheres  employ  the  lower 
ganglia  of  the  brain  in  effecting  certain  co-ordinations  of  sensation 
and  motion  ;  it  may  even  be  said  that  the  end-organs  of  sense 
communicate  with  the  supreme  central  organs  by  means  of  the 
afferent  nerve-tracts  and  the  lower  ganglia.  All  such  language  ex- 
presses, correctly  enough  for  popular  usage,  the  undoubted  fact 
that,  in  the  complicated  relations  of  position  and  motion  which  are 
maintained  among  the  different  members  of  the  nervous  system,  a 
certain  order  of  action  is  constantly  preserved.  Changes  originate 
in  one  part,  and  are  propagated  to  other  contiguous  or  more  distant 
parts.  In  such  propagation  of  the  changes  a  regular  tract  of  the 
advancing  motions  is  assumed  always  to  exist ;  and  thus  the  parts 
that  lie  between  the  extremes  may  be  looked  upon  as  means  or 
media — as  instrumental  to  the  completion  of  the  process.  For  ex- 
ample, in  quick  succession  upon  a  certain  idea  of  motion,  and  a  vo- 
lition to  a  definite  motion,  my  arm  is  raised  or  my  whole  body 
changes  its  position  in  space.  How  can  this  come  about  ?  To  the 
inexperienced  person  the  result  seems  to  be  an  "  immediate  "  ef- 
fect of  the  will — that  is,  no  apparent  media  or  instruments  stand 
between  the  volition  and  the  subsequent  changes  in  the  relations  of 
the  masses  of  the  body  to  other  objects. 

The  vulgar  persuasion  undoubtedly  is,  that  a  man  immediately 
41 


642  MIISTD    AND    ITS    ORGAN. 

knows  himself  to  be  the  cause  of  the  movement  of  his  own  arms  oi 
legs  ;  that  he  knows  that  he  can  move  them  if  he  will.  Little  in- 
vestigation, however,  is  needed  to  discover  that  such  is  in  no  respect 
the  state  of  the  case.  A  thousand  hidden  links,  any  one  of  which 
might  drop  out  without  our  being  immediately  aware  of  it,  inter- 
vene between  the  volition  and  the  actual  motion.  No  one  directly 
knows  that  one  can  move  as  one  will ;  one  knows  that  one  can  will, 
and  infers  that,  if  one  will,  the  movement  will  follow.  In  tracing 
the  line  of  physical  sequences  backward  from  the  motion  of  the 
limb  toward  the  arising  of  the  volition  in  consciousness,  we  bring 
it  to  a  termination  in  a  hypothetical  nerve-commotion  in  some  (so- 
called  "motor")  area  of  the  brain.  At  this  point  the  line  of 
sequences,  considered  as  a  succession  of  modes  of  motion,  draw- 
ing constantly  nearer  to  the  instant  of  the  volition,  comes  to  an 
end.  The  connection  beyond  and  into  that  state  of  consciousness 
which  is  called  a  "  volition "  cannot  be  conceived  of  as  the  pro- 
gressive propagation  of  a  peculiar  molecular  motion  called  nerve- 
commotion. 

§  9.  It  is  obvious  from  the  foregoing  remarks  that  one  part  of 
the  nervous  mechanism  can  be  said  to  be  the  "  organ  "  or  instru- 
ment of  another  part,  in  a  meaning  of  the  word  which  cannot  prop- 
erly aj^ply  to  the  relation  of  the  brain  and  the  mind.  In  a  certain 
justifiable  meaning  of  the  word,  all  the  rest  of  the  body  may  be 
said  to  be  the  organ  of  the  brain.  That  is  to  say,  those  changes  in 
the  molecules  of  the  brain's  substance  which  arise  there — whether 
because  of  certain  ideas  and  volitions  of  the  mind,  or  because  of 
changes  in  the  character  of  the  blood-supply,  or  of  sensory  imjDulses 
thrown  in  from  the  periphery  or  other  lower  nervous  centres — get 
themselves  expi-essed  through  the  other  members  of  the  body.  All 
this  system  of  instrumentalities  or  interdependent  organs  is  of  one 
nature.  It  consists  of  material  particles  having  a  definite  chemical 
constitution,  structure,  and  arrangement  in  space ;  its  functions  are 
all  modes  of  motion  of  such  particles.  One  part  serves  as  an  instru- 
ment or  "  organ  "  for  another,  because  the  changes  in  the  former 
effect  changes  elsewhere,  not  directly,  but  through  contiguous  and 
connected  parts.  If  the  necessary  contiguous  parts  are  wanting 
or  their  relations  disarranged,  if  the  connection  is  interrupted  or 
destroyed,  then  the  work  cannot  be  done;  the  "organ,"  "instru- 
ment," or  "  means,"  is  lacking. 

What  is  true  of  the  relations  described  by  the  word  "organ," 
as  these  relations  exist  between  any  two  parts  of  the  nervous 
mechanism,  is  only  partially  true  of  the  relations  which  exist  be- 
tween any  particular  portion  of  this  mechanism  and  the  phenom- 


THE   USES    OF   THE   BRAIX.  643 

en  a  of  consciousness.  In  other  words,  only  a  part  of  the  real  rela- 
tions existing  between  mind  and  brain  can  properly  be  described 
under  such  terms  as  "organ,"  "instrument,"  etc.  The  brain, 
with  its  appropriate  functions,  is  an  indispensable  medium  between 
certain  changes  in  the  peripheral  parts  of  the  body  and  correspond- 
ing changes  in  the  states  of  consciousness.  If  ideas  of  motion  and 
volitions  to  move  are  to  be  followed  by  actual  motions  correspond- 
ing to  the  ideas  and  volitions,  then  the  brain  must  act  with  its  ap- 
propriate functions.  The  motions  can  be  executed,  if  at  all,  only 
through  the  brain.  As  much  as  this  is  true  of  all  the  efferent  tracts 
which  lead  from  the  cerebral  cortex  through  the  lower  portions  of 
the  encephalon,  along  the  spinal  cord,  and  out  to  the  particular 
groups  of  muscles.  Something  more  and  special  is,  however,  true 
of  the  brain.  It  is  the  first  of  the  indispensable  physical  links  in 
the  whole  chain  ;  it  stands  nearest,  as  it  were,  to  the  mind.  All 
the  other  steps  in  the  execution  of  the  ideas  and  volitions  of  the 
mind  depend  upon  what  takes  place  in  the  brain.  If  nothing 
takes  place  here,  nothing  at  the  periphery  of  the  body  will  come 
from  the  volitions  ;  if  anything  wrong  takes  place  here,  all  that 
goes  on  at  the  periphery  will  be  wrong,  and  the  mind  will  not  get 
its  volitions  executed.  In  this  sense,  at  least,  the  brain  is  the  par- 
ticular organ  of  the  mind  ;  it  is  the  most  intimate  and  indispen- 
sable means  for  the  execution  of  all  its  ideas  or  volitions  of  motion. 

It  does  not  appear  that  the  foregoing  statement  by  any  means 
exhausts  the  description  of  the  experience,  reflection  upon  which 
induces  us  to  regard  the  brain  as  the  '•  organ  "  of  the  mind.  For 
the  brain  seems  to  serve  as  the  special  physical  basis  of  the  ideas 
and  volitions  of  motion  themselves.  After  experience  in  moving 
a  particular  member  of  the  body  has  once  been  gained,  that  mem- 
ber may  be  lost ;  and  yet  if  the  proper  areas  of  the  brain  remain 
unimpaired,  the  ideas,  feelings,  and  volitions  connected  with  the 
movement  of  the  lost  member  will  still  arise  in  the  mind.  The  man 
whose  leg  or  arm  has  been  amputated  can  still  feel  it,  can  form  the 
image  of  how  it  should  be  moved  to  be  in  this  position  or  in  that, 
and  even  will  to  have  it  moved.  The  leg  is  not,  then,  the  organ  of 
these  ideas,  feelings,  and  volitions. 

Experiments  with  animals,  by  extirpating  the  cortical  areas,  and 
observation  of  human  pathological  cases — especially,  perhaps,  in 
certain  forms  of  aphasia  (comp.  Part  II.,  chaps.  I.  and  11.)— seem 
clearly  to  show  that  a  much  more  intimate  relation  exists  between 
the  brain  and  the  mind.  With  the  destruction  or  derangement  of 
certain  of  its  areas,  the  power  even  to  form  such  ideas  and  volitions, 
or  to  have  such  feelings,  seems  to  be  impaired  or  lost.     We  cannot 


644  MIJSTD   AND   ITS   OEGAN. 

say,  to  be  sure,  that  the  mind  has  lost  a  part  of  its  general  faculty 
to  conceive,  to  feel,  and  to  will.  It  has,  however,  suffered  in  respect 
to  its  power  to  frame  a  certain  set  of  definite  ideas  and  volitions  as 
I'espects  the  motion  of  the  peripheral  members.  This  class  of  facts 
is  certainly  calculated  to  emphasize  strongly  our  conception  of  the 
brain  as  being,  in  a  special  sense,  the  indispensable  means  through 
which  the  states  of  consciousness  are  related  to  changes  in  the 
position  of  molecules  and  masses  of  matter.  Thus  much,  then,  we 
are  also  entitled  to  include  in  our  declaration  that  the  brain  is  the 
"  organ  "  of  the  mind. 

There  is  another  most  important  class  of  facts  which  may  be  par- 
tially described  under  the  same  terms  as  the  foregoing.  The  brain 
is  the  indispensable  means  for  furnishing  the  mind  with  its  sensa- 
tions, and  so  with  its  presentations  of  sense  or  perceptions  of  things. 
This  statement  is  not  to  be  understood  as  though  the  brain  could, 
of  itself,  construct  the  sensations  and  perceptions  and  hand  them 
over  ready-made,  as  it  were,  to  the  mind.  Sensations  are  states  of 
consciousness,  not  modes  of  the  brain  ;  and  even  when  they  are 
synthetically  united,  localized,  and  projected  to  the  periphery  of 
the  body,  or  into  surrounding  space,  they  are  brought  under  no 
essentially  new  relations  to  the  nervous  mechanism.  Sensations 
are  not  nerve-commotions,  "  etherealized  "  by  the  optic  thalami  and 
cerebral  convolutions,  and  then  handed  over  to  consciousness. 
Therefore  the  instrumental  relation  between  brain  and  mind  is 
not  that  of  transmitting  a  peculiar  kind  of  motion  from  one  phase 
into  another,  or  from  one  being  to  another.  The  brain  is  not  the 
"  organ  "  of  the  mind  in  the  sense  in  which  a  being  that  starts  or 
receives  some  mode  of  motion  becomes  instrumental  for  the  pro- 
duction of  changes  in  another  being.  Nevertheless,  no  sensations 
will  arise  in  the  mind  unless  the  brain  be  affected  in  a  certain  way. 
Looking  at  the  chain  of  sequences  as  it  runs  from  v^'ithout  inward, 
we  might  say  :  The  brain  is  the  organ,  or  instrument,  through 
which  the  stimuli  of  the  outside  world,  acting  on  the  end- organs  of 
sense,  finally  reach  the  mind. 

What  is  properly  meant  by  speaking  of  the  brain  as  the  mind's 
organ  of  sensation  is,  strictly  speaking,  to  be  described  as  follows  : 
The  brain  is  the  last  and  most  important  physical  antecedent  to  the 
mind's  being  affected  with  the  different  sensations.  The  eye,  ear, 
nose,  etc.,  are  jDopularly  called  organs  of  sense.  Nothing  is  more 
obvious  about  the  whole  process  of  sensation  than  the  part  played 
in  it  by  the  peripheral  sensory  organs.  It  is  apparently  through 
these,  by  means  of  these,  only  on  condition  of  the  acting  of  these, 
that  sensations  arise  in  the  mind.     Further  examination  shows, 


MATERIAL    COlSTISrECTIOlSr   IMPOSSIBLE.  645 

however,  that  the  end-organs  of  sense  are  more  remotely  connected 
with  the  origin  of  sensations  than  might  at  first  be  supposed. 
Excitement  of  the  afferent  nerve-tracts  between  the  end-organs 
and  the  brain  will  also  produce  sensations.  If  these  sensations  are 
not  so  refined  and  complex  as  those  which  are  caused  by  stimu- 
lating the  end-organs  tbemselves,  the  reason  is  to  be  found  in  the 
fact  that  we  cannot  stimulate  the  afferent  nerves  in  the  way  to  pro- 
duce such  sensations  except  through  the  appropriate  end-organs. 
Still  further  examination  shows  that  the  value  of  the  stimulus  ap- 
plied to  the  afferent  nerves  for  the  production  of  sensation  is  en- 
tirely dependent  upon  what  the  conducting  organs  convey  to  the 
brain,  according  to  their  specific  nature  and  appropriate  connections. 
Sensations  can  be  equally  well  produced  by  stimulating  the  cerebral 
substance  directly.  When  drugs,  or  gases,  or  diseases,  or  increased 
action  of  the  blood-vessels  change  the  character  of  the  blood-supply, 
we  see,  and  hear,  and  feel  a  world  of  things  that  has  no  existence 
for  the  end-organs  of  sense.  The  brain  is  then  the  "organ"  of 
sensation  for  the  mind,  in  the  sense  of  being  the  indispensable  and 
most  immediate  means  for  the  production  of  sensation. 

Nothing  that  has  just  been  said  interferes  in  the  least  with  the 
valid  claim  for  the  mind,  that  it  alone  is  the  producer  of  every  sen- 
sation ;  or,  in  other  words,  all  sensations  are  modes  of  the  behav- 
ior of  a  being  that  is  non-material  and  a  unit-being,  and  is  called 
Mind.  When  the  physical  conditions  are  fulfilled  in  the  brain,  and 
according  to  the  way  in  which  they  are  fulfilled,  the  mind  itself 
puts  forth  the  phenomena  of  sensation.  For  the  sensations  are 
not  copies  of  outside  material  molecules,  whether  acting  on  the 
end-organs  of  sense  or  acting  as  excited  nervous  substance  in  the 
brain  ;  it  can  scarcely  be  repeated  too  often — they  are  modes  of 
the  conscious  activity  of  mind. 

§  10.  Still  another  class  of  attempts  to  generalize,  and  embody 
in  a  single  term,  the  various  essential  relations  of  the  brain  to  the 
mind  leads  to  the  inquiry  after  some  one  special  "  connection  "  or 
"  bond  "  between  the  two.  How  are  mm d  and  brain  connected  ? 
What  real  tie  binds  them,  so  that  they  are  obliged  to  have  re- 
gard to  each  other  in  the  modes  of  their  behavior  ?  Here,  again, 
any  too  literal  answer  to  this  inquiry  leads  at  once  to  manifest 
absurdity.  A  material  bond  designed  to  unite  mind  and  brain 
might  perhaps  be  conceived  of  as  connected  with  the  latter,  and 
yet  as  remaining  material  ;  but  in  order  to  make  it  connect  with 
the  former  (the  mind)  it  would  have  to  become  non-material,  un- 
less we  are  ready  to  concede  that  the  material  and  the  non-material 
can  stand  connected  without  some  special  bond.     In  case  this  con- 


d46  CONNECTIOJS"    OF   BRAIN   AND   MIND. 

cession  is  once  made,  however,  we  cease  to  feel  the  need  of  a 
special  bond  between  the  mind  and  the  brain. 

If  it  be  at  once  admitted  that  no  connection  is  to  be  sought,  or 
can  be  found,  between  the  mind  and' the  brain,  beyond  the  fact  that 
their  modes  of  behavior  are  mutually  dependent,  it  will  not  be 
necessary  to  appeal  to  any  special  mystery.  What  bond  connects 
together  the  jjlanets  of  the  solar  system  so  that  each  one  moves  in- 
variably witli  reference  to  the  position  of  all  the  others,  and  yet 
in  a  path  peculiarly  its  own  ?  We  can  only  respond  by  talking  of 
the  force  and  laws  of  gravitation.  These  "laws,"  however,  are 
simply  a  mathematical  statement  of  the  uniform  modes  of  the  be- 
havior of  certain  physical  beings;  this  "force"  is  no  entity  or 
bond  connecting  the  individuals  with  each  other,  as  the  rods  of 
the  orrery  bind  its  parts  to  a  common  centre.  Did  such  rods 
exist  to  bind  the  planets  to  the  sun,  we  should  still  have  to  inquire 
for  some  bond  between  the  particles  of  the  rods  ;  and  for  another 
bond  to  unite  the  atoms  into  these  jDarticle§.  Nor  would  it  be  an 
answer  to  such  inquiry  to  discourse  of  cohesion  and  of  chemical 
afl&nity,  or  of  the  laws  which  control  the  action  of  those  forces. 
For  cohesion  and  chemical  affinity  are  not  special  bonds  ;  they, 
too,  are  but  expressions  for  the  facts  that  the  elements  of  material 
reality,  under  certain  conditions  and  according  to  the  kind  to 
which  they  belong,  behave  as  though  bound  ;  these  elements  be- 
have, that  is  to  say,  according  to  what  they  are,  and  according  to 
the  relations  in  which  they  stand  to  each  other. 

No  more  obscure  and  ud satisfactory  is  our  knowledge  concern- 
ing the  "bond"  which  unites  body  and  soul,  or,  more  especially, 
the  mind  and  the  brain.  The  brain  is  a  vast  collection  of  material 
molecules,  connected  together  in  a  great  variety  of  ways,  which 
always  act,  as  it  were,  with  their  own  chemical  constitution,  and 
relations  to  other  similarly  constituted  bodies,  fully  in  mind. 
Even  the  molecules  are  not  bound  to  each  other  by  any  one  dis- 
coverable or  conceivable  bond.  So  far  as  we  can  speak  of  them  as 
"  connected  "  at  all,  they  are  connected  by  a  great  variety  of  bonds. 
Each  of  these  bonds  depends  upon  the  nature  of  the  molecules 
which  enter  into  it,  and  upon  the  manner  in  which  each  molecule 
is  related  to  other  molecules.  Essentially  the  same  thing  is  true 
— and  perhaps  with  no  more  of  ultimate  mystery  in  its  truthful- 
ness— of  the  connection  between  mind  and  brain.  The  mind  is  a 
conscious  being,  a  being  that  perceives,  feels,  remembers,  imagines, 
thinks,  and  wills.  In  respect  to  certain  classes  of  its  activities,  at 
least,  what  it  does  depends  upon  what  is  done  by  the  molecules  of 
the  brain  with  which  it  is,  as  we  say,  specially  connected.    The  con- 


BODY    AS   TENEMENT   OF   SOUL.  647 

nection  is  not,  however,  sucli  as  can  be  explained  by  assuming 
one  special  form  of  a  "  bond  "  between  the  two.  An  infinite  variety 
of  relations,  some  of  which  are  in  a  measure  reducible  under  law, 
and  others  of  which  elude  all  attempts  thus  to  subject  them,  exists 
between  the  unit-being  called  mind,  and  the  composite  structure 
and  varied  functions  of  the  brain.  The  connection  is  no  less  real, 
however,  because  invisible  ;  no  less  valuable  and  cei'tain,  because 
not  one  bond,  but  an  infinite  variety  of  relations. 

§  11.  It  will  scarcely  be  supposed  that  information  of  scientific 
value  concerning  the  nature  of  the  real  connection  between  the 
bod}'  and  the  soul  can  be  obtained  from  terms  which  are  almost 
purely  figurative  and  poetic.  The  limited  and  defective  nature  of 
our  sense-perceptions,  the  misery  of  much  of  life,  the  unrealized 
longings  for  knowledge  and  happiness,  and  the  work  of  imagina- 
tion in  framing  a  picture  of  some  state  of  existence  in  which  the 
limitations  are  removed  and  the  longings  realized,  have  led  men  in 
all  ages  to  regard  the  body  as  the  "  prison  "  of  the  soul.  Because 
the  senses  are  not  more  in  number  than  they  really  are,  or  more 
far-reaching  and  accurate  than  their  construction  permits  them  to 
be,  they  are  regarded  as  restraining  the  soul,  rather  than  as  bringing 
it  information  which  has  the  character  of  satisfying  reality.  The 
brevity  and  uncertainty  of  life,  and  the  speed  with  which  accident 
and  disease  impair  or  dissolve  the  bodily  functions,  together  with 
the  persuasion  that  the  thinking  principle  will  have  a  continued 
existence,  suggest  the  reflection  :  the  body  is  the  "tenement"  or 
"  tabernacle  "  of  the  soul. 

However  true  and  comforting  the  foregoing  hopes  and  reflec- 
tions may  be,  it  cannot  be  claimed  that  they  throw  any  clear  light 
on  the  subject  of  our  investigation.  Physiological  Psychology 
rests  upon  such  facts  as  show  a  most  intimate  and  unceasing  cor- 
relation between  the  body  and  the  soul.  It  can  never,  therefore, 
consider  the  ultimate  connection  of  the  two  as  though  it  were  as 
unimportant  and  superficial  as  that  between  the  prisoner  and  the 
prison  which  holds  him,  or  between  the  tenant  and  the  tenement  or 
tent  which  for  the  time  being  is  his  abode.  We  are  not  at  present 
engaged  in  considering  the  evidence  that  the  mind  is  immortal, 
and  can  exist  apart  from  this  body  and  in  another  body,  if  not 
apart  from  all  bodies  ;  nor  even  the  proof  that  its  nature  is  vastly 
superior  to  that  of  all  the  material  structures  to  which  it  might  be- 
come related.  We  are  rather  testing  the  assumption  that  the  mind, 
as  connected  with  the  brain,  is  a  real  being  which,  although  depend- 
ent upon  what  occurs  in  the  brain  for  its  character  and  the  order 
of  its  activities,  has  nevertheless  that  existence  which  belongs  to 


648  coNNECTioisr  of  brain  and  mind. 

all  real  beings — a  nature  and  a  development  of  its  own.  This  as« 
sumption,  indeed,  is  applied  and  confirmed  in  every  attempt  to 
characterize  the  real  connection  which  exists  between  the  mind 
and  the  brain — whether  the  words  "seat,"  "  organ,"  "instrument," 
or  other  corresponding  words  be  used. 

§  12.  Thus  far  little  has  been  exphcitly  said  as  to  the  propriety 
of  applying  the  terms  of  "  causation  "  (such  as  "  energy,"  "  action," 
"force,"  "impulse,"  "effective  agency,"  etc.)  to  the  case  of  mind 
and  brain.  Yet  everything  which  has  been  said  has  implied  that 
these  terms  are  really  applicable.  There  would  be  no  advantage  to 
the  mind  in  being  "  seated  "  in  the  brain — that  is,  in  being  under 
any  special  relations  to  a  given  extent  of  nervous  matter — unless  it 
were  somehow  influenced  or  acted  upon  by  this  nervous  matter,  and 
could  in  turn  influence  and  act  upon  it.  No  "organ "or  instru- 
ment is  of  any  use  whatever — that  is,  no  thing  can  become  an  organ 
or  instrument — unless  it  can  be  acted  upon  by  that  which  employs 
it  as  an  organ,  and  can  in  its  turn  act  upon  other  things.  Action 
of  mind  on  brain  is  implied  in  calling  the  latter  the  organ  of  the 
mind's  volitions  ;  action  of  brain  on  mind  is  implied  in  calling  it 
the  organ  of  the  mind's  sensations.  To  act  and  to  be  acted  upon 
is  equivalent  to  standing  in  the  relation  of  cause  and  effect. 

It  is  not  at  present  necessary  to  point  out  in  detail  how  much  of 
obscurity  and  contradiction  are  involved  in  all  the  more  popular 
ways  of  mentally  representing  the  foregoing  relation.  The  trans- 
mission of  energy  (or  force)  is  popularly  spoken  of  as  though  such 
energy  streamed  off  from  one  body  and  attached  itself  to  another  ; 
and  as  though  the  quantity  of  energy  thus  given  off  were  dependent 
upon  the  strength  of  the  blow  given  by  one  body  to  another.  Let  it 
be  supposed,  however,  that  the  application  of  the  law  of  causation  to 
the  case  of  brain  and  mind  is  made  in  the  most  approved  manner. 
It  is  simple  matter  of  fact,  as  tested  by  thousands  of  observations 
and  experiments,  that  changes  in  the  condition  and  functional  ac- 
tivity of  the  nervous  centres  are  followed  by  changes  in  states  of 
consciousness,  in  a  regular  way  ;  and  that,  conversely,  changes  of 
the  latter  sort  are  followed  by  changes  in  the  relations  of  the 
masses  of  the  body,  and  of  the  functional  activity  of  nervous  cen- 
tres and  end-organs  of  sense.  Now,  unless  we  are  ready  to  be 
satisfied  with  simply  stating  the  facts,  without  making  the  at- 
tempt to  find  any  rational  account  for  them,  we  are  obliged  to  con- 
sider these  correlated  changes  under  the  terms  of  cause  and  effect. 
That  is  to  say,  we  regard  the  mind  as  a  real  being  with  activities 
called  states  of  consciousness,  and  the  brain  as  a  collection  of  real 
beings   called  moving  molecules  of  nervous   matter,  and  we  aS' 


INFLUENCE   OF   THE   CEREBEAL   CIRCULATION.  649 

sume  that  the  latter  acts  upon  the  former  and  is  acted  upon  by  it 
in  turn.  In  other  words,  brain  and  mind  are  conceived  of  as  really? 
connected  under  the  law  of  causation. 

Were  it  not  for  the  influence  of  prejudice  derived  from  specula- 
tion upon  certain  philosophical,  ethical,  and  religious  questions,  no 
one  would  think  of  hesitating  to  apply  the  terms  of  causation  to 
the  case  of  mind  and  brain.  The  stoppage  of  the  arteries  leading 
to  the  cerebrum,  by  outside  pressure  or  by  embolism,  is  speedily 
and  regularly  followed  by  a  disturbance  or  cessation  of  conscious- 
ness. Who  doubts  that  a  man  loses  his  senses  as  truly  as  he  loses 
a  portion  of  his  brain-mass,  because  he  has  been  struck  a  blow  upon 
the  head  ?  The  falling  of  waves  of  light  or  sound  upon  the  eye  or 
ear,  the  contact  of  the  hand  with  the  hard  substance  of  the  metal 
or  wood,  the  breathing  of  the  air  into  the  nostrils,  are  universally 
regarded  as  the  causes  of  the  sensations  and  perceptions  which 
follow.  The  general  impression  undoubtedly  is,  that  the  act  of 
will  is  the  cause  of  the  motion  of  the  different  limbs  or  of  the  en- 
tire body.  In  each  of  these  cases  more  careful  observation  I'esults 
in  supplying  many  links  in  the  chain  of  causation  which  the  popu- 
lar account  has  overlooked.  The  result  is  a  more  minute  and 
careful  picture  of  those  molecular  changes  which  take  place  in  the 
cerebral  substance,  as  induced  by  the  severe  shock  of  the  blow  or 
by  the  gentle  stir  of  the  stimulus  acting  through  the  end-organs  of 
sense.  Science  explains  the  way  in  which  the  visible  changes  in 
the  position  of  the  ponderous  masses  of  the  body  are  due  to  ante- 
cedent invisible  changes  in  the  molecules  of  the  muscles,  of  the 
efferent  nerves,  and  of  the  lower  and  the  supreme  nervous  centres. 
But  all  this  explanation  implies  the  application  of  terms  of  causation 
to  the  entire  chain  of  physical  events  ;  and  if  these  events  are  to  be 
considered  as  in  any  measure  explaining  the  psychical  events  with 
which  they  are  connected  in  time,  the  relation  of  the  two  classes  of 
events  is  also  assumed  to  be  one  capable  of  statement  in  the  same 
terms. 

How  impossible  it  is  to  avoid  speaking  of  the  connection  of  mind 
and  brain,  in  terms  of  causation,  may  be  illustrated  by  the  relations 
between  the  condition  of  the  intercranial  blood- supply'  and  the 
states  of  consciousness.  The  character  of  the  cerebi'al  circulation 
is  said  to  have  a  great  "  influence  "  upon  the  condition  of  the  mind. 
A  slight  increase  of  this  circulation,  resulting  from  a  small  quantity 
of  alcohol  or  other  drugs,  or  from  the  hearing  of  interesting  news, 
produces  an  increased  speed  in  the  mental  train.  Keaction-time  is 
found  to  vary  with  changes  in  the  circulation.  In  the  delirium  of 
fever  the  wild  and  quickly  moving  condition  of  the  thoughts,  fan- 


650  CONISrECTION   OF   BRAIlSr   AND   MIND. 

cies,  and  sensations  is  a  direct  expression  of  the  kind  of  work  which 
is  going  on,  because  of  the  accelerated  heart-beat  and  the  disor- 
dered character  of  the  blood,  within  the  cerebral  arteries.  Schroe- 
der  van  der  Kolk  tells  of  a  patient  who,  when  his  pulse  was  reduced 
by  digitalis  to  50  or  GO  beats  per  minute,  was  mentally  quiet  and 
depressed  ;  when  it  was  allowed  to  rise  again  to  90  beats,  his 
mind  was  in  maniacal  confusion.  Cox  narrates  the  case  of  a  sick 
man  who,  at  40  pulsations  in  the  minute,  was  "  half-dead  ;  "  at  50, 
melancholic;  at  70,  quite  "beside  himself;"  at  90,  raving  mad. 
The  character  of  dreams  is  determined,  to  a  considerable  extent, 
by  the  position  of  the  head  and  the  way  in  which  this  position 
affects  the  cranial  circulation.  Hallucinations  not  infrequently  are 
immediately  made  to  cease,  when  the  person  having  them  assumes 
the  standing  posture,  or  has  leeches  applied  to  the  head. 

§  13.  Objections  have  arisen  from  various  sources,  and  have  been 
urged  with  various  degrees  of  skill  and  intensity,  against  applying 
the  concej)tion  of  causation  to  the  relations  of  mind  and  brain.  So 
far  as  these  objections  are  more  purely  ethical  or  religious,  it  is  not 
consistent  with  the  purpose  of  the  present  investigation  to  consider 
them.  But  certain  objections  are  more  jDurely  scientific,  or  per- 
haps philosophical,  upon  a  basis  of  observed  physical  and  psycho- 
logical facts.  A  brief  examination  of  such  objections  is  not  only 
consistent  with  the  present  investigation,  but  even  required  by  it. 

Among  the  followers  of  the  Cartesian  philosophy  it  was  held 
that  body  and  soul  cannot  really  act  upon  each  other,  because  of 
the  obvious  difference  in  the  essential  characteristics  of  the  two. 
The  body  is  extended  and  material ;  the  soul,  being  non-material, 
does  not  possess  the  characteristic  most  distinctive  of  all  that 
comes  under  the  conception  of  matter.  Matter  and  mind,  as  being 
in  their  very  essence  opposed,  are  sepai-ated  from  each  other  by  the 
whole  diameter  of  being.  They  cannot  be  regarded  as  united  directly 
through  any  real  tie,  but  stand  at  the  mutually  exclusive  poles  of 
being.  That  a  certain  marked  corresjDondence  exists  between  the 
phenomena  of  the  extended  and  material  body  and  the  phenomena 
of  the  conscious  non-material  soul  plainly  cannot  be  denied  ;  and 
some  account  for  this  correspondence  must  be  given.  No  one  can 
doubt  that  his  sensations,  in  their  quality  and  order  of  succession, 
are  related  to  certain  events  in  the  physical  organs  of  his  own 
body  ;  neither  is  it  easy  to  persuade  one's  self  that  one's  move- 
ments are  not,  at  least  in  some  indirect  way,  "  ordered  "  by  one's 
desires  and  volitions  respecting  them. 

To  account  for  the  obvious  regular  relation  between  bodily 
changes  and  mental  phenomena,  two  or  three  somewhat  different 


THEORY    OF   OCCASIOlSrALISM:.         "  651 

theories  may  be  proposed.  One  of  these  is  the  so-called  doctrine 
of  "  Occasionalism."  According  to  this  doctrine  body  and  mind 
do  not  stand  in  the  relation  of  cause  and  effect  toward  each  other  ; 
neither  one  ever  really  acts  upon  the  other.  But  on  occasion  of 
some  event  of  a  definite  kind  happening  iu  the  bodily  realm,  a 
corresponding  event  of  its  own  definite  kind  happens  in  the  domain 
of  consciousness  ;  and  vice  versa.  To  say  this,  however,  is  plainly 
in  itself  nothing  more  than  to  repeat  the  facts  of  experience  over 
again,  but  without  offering  any  explanation  of  them.  Since  some 
real  "  ground  "  or  reason  that  shall  have  causal  efficiency  seems 
needed  in  order  to  explain  why  body  and  mind  should  take  "occa- 
sion "  to  act  at  all,  in  view  of  each  other's  action,  theology  readily 
finds  such  ground  in  the  Divine  Being.  God,  it  is  said,  on  occasion 
of  an  event  occurring  in  either  of  the  two  diametrically  opposed 
spheres,  causes  the  right  corresponding  event  to  occur  in  the  other 
sphere.  Matter  and  mind  are  not  causally  connected  immediately 
with  each  other  ;  they  are  causally  connected  only  through  a  com-*- 
mon  ground  in  God.  Pure  Occasionalism,  however,  seems  to 
make  too  large  demands  upon  a  pious  credulity.  To  be  always 
observing  mere  "  occasions,"  in  order  to  cause  body  and  mind  to 
keep  the  right  pace  with  each  other,  may  well  be  regarded  as  un- 
worthy of  Divine  Being.  To  meet  this  difficulty  the  theory  of 
"  Pre-established  Harmony  "  is  devised.  According  to  this  theory 
God  has  eternally  predestined  the  entire  succession  of  events  in 
the  world,  down  to  every  minutest  detail.  Body  and  mind,  there- 
fore, may  be  regarded  as  like  two  clocks  which  have  been  so  con- 
structed that,  without  either  having  any  effect  upon  the  other,  they 
go  on  exactly  as  though  one  were  actually  moved  by  the  other. 

It  would  scarcely  be  worth  while  ,  to  consider  seriously  these 
older  forms  of  the  denial  that  any  real  causal  relation  exists  be- 
tween body  and  mind,  were  it  not  for  the  fact  of  their  essential 
agreement  with  more  modern  forms  of  the  same  denial.  Two  re- 
marks upon  the  foregoing  theories,  in  special,  are  necessary.  The 
assumption  that  matter  and  mind  are  sepai-ated  from  each  other 
''  by  the  whole  diameter  of  being,"  if  it  be  held  to  mean  that 
the  two  forms  of  being  are  so  disparate  in  nature  as  to  be  unable 
to  act  on  each  other,  is  an  unverifiable  assumption.  It  even  goes 
squarely  in  the  face  of  many  of  the  most  important  psycho-physical 
facts.  We  know  nothing  about  what  kind  of  beings  can  or  can- 
not act  on  each  other,  except  through  our  experience  of  what 
beings  do  actually  act  upon  each  other.  The  mystery  involved  in 
any  one  being  acting  on  any  other  is  equally  deep  and  unfathom- 
able, in  whatever  direction  we  attempt  to  explore  it.     Before  ex- 


652  CONNECTION    OF   BRAIN   AND   MIND. 

perience  with  the  facts,  we  should  be  quite  at  a  loss  to  tell  whethei 
atoms  of  oxygen  could  act  on  atoms  of  hydrogen,  under  the  laws 
of  chemical  affinity,  or  not ;  whether  molecules  of  iron  could  act 
on  other  molecules  of  iron,  under  the  laws  of  cohesion,  or  not, 
etc.  How  it  is  that  material  masses  or  molecules  can  "influence" 
each  other,  or  what  is  the  real  nature  of  the  force  which  binds 
them  together,  physical  science  is  quite  unable  to  say.  So  that, 
even  if  we  were  entitled  to  regard  matter  as  somewhat,  the  very 
essence  of  which  it  is  to  be  spread  out,  and  mind  as  somewhat, 
the  very  essence  of  which  it  is  to  be  conscious  and  not  to  be  spread 
out,  we  should  still  be  quite  without  justification  in  asserting  (a 
priori,  as  it  were)  that  one  cannot  act  upon  the  other.  But — just 
the  contrary — if  we  are  to  accept,  unbiased,  the  obvious  witness  of 
the  facts,  we  are  compelled  to  affirm  :  The  phenomena  of  mind 
and  the  conditions  of  the  brain  are  related  so  constantly  and  im- 
mediately under  law,  that  we  are  warranted  in  beheving  in  the 
action  of  each  upon  the  other. 

Moreover,  the  theory  of  Occasionalism,  Pre-established  Har- 
mony, and  all  similar  theories,  do  not  in  the  least  assist  us  to  es- 
cape the  difficulties  which  attach  themselves  to  every  conception 
of  causation.  "We  cannot  regard  the  Divine  Being  as  bringing 
about  a  change  in  either  mind  or  body,  on  "  occasion  "  of  some 
other  change,  without  assuming  that  mind  (the  Infinite  Mind) 
stands  in  the  causal  relation  to  matter.  Furthermore,  we  cannot 
conceive  of  a  "  reason  "  why  this  Being  should  eifect  one  change 
rather  than  another,  without  I'egarding  Him  as  subjecting  himself 
to  the  same  relation. 

'  §  14.  It  is  interesting  to  notice  certain  relations,  both  of  similar- 
ity and  of  difference,  between  a  prominent  modern  theory  as  to  the 
mutual  action  of  mind  and  brain  and  the  now-abandoned  views 
of  Occasionalism  and  Pre-established  Harmony.  Modern  science 
raises  most  of  its  objections,  against  regarding  the  conditions  of  the 
central  nervous  system  and  the  states  of  consciousness  as  connected 
by  a  real  causal  tie,  out  of  a  profound  regard  for  matter  and  the 
laws  of  physics.  The  great  value  and  significance  of  physical  phe- 
nomena, and  the  regular  modes  of  their  recurrence,  if  not  the  in- 
dependent and  eternal  existence  of  material  beings,  are  taken  for 
granted  by  this  theory,  whatever  difficulties,  feai's,  or  hopes  to  the 
contrary  may  arise  from  the  sphere  of  mind.  Elements  of  ma- 
terial reality  (called  "  atoms ")  are  assumed  to  exist ;  the  univer- 
sal form  of  their  relation  is  held  to  be  the  law  of  the  conservation 
and  correlation  of  energy.  By  "  energy "  we  are  to  vmderstand 
that  which  moves  or  tends  to  move  the  elementary  atoms,  or  their 


NO   TRANSMISSION   OF   ENEEGY.  653 

aggreg-ations,  into  molecules  and  masses.  The  energy  wliich  is  re- 
garded as  causing  actual  motion  is  kinetic  ;  that  which  is  to  be 
regarded  as  tending  to  produce  motion  is  stored  or  potential.  But 
inasmuch  as  we  have  no  test  or  suggestion  of  the  presence  of  en- 
ergy except  motion,  we  seem  compelled  to  consider  the  so-called 
"  tendency  "  to  move  (potential  energy)  as  motion  that  is  beyond 
the  sphere  of  the  senses,  because  distributed  over  so  vast  a  number 
of  minute  portions  of  matter  whose  amount  of  motion  is  too  small 
to  be  discoverable.  All  physical  elements  and  masses  are,  accord- 
ingly, always  in  motion,  and  the  total  quantum  of  this  motion  is 
invariable  throughout  the  entire  universe.  All  forms  of  energy 
must  be  classified,  as  respects  quality,  by  the  kind  of  their  motion  ; 
and  as  respects  degree,  by  the  amount  of  their  motion. 

On  attempting  to  account  for  the  whole  world  of  phenomena  in 
terms  of  motion,  kinetic  or  potential,  under  the  law  of  the  conser- 
vation and  correlation  of  energy,  we  are  met  with  insuperable  diffi- 
culty as  soon  as  we  enter  the  domain  of  consciousness.  States  of 
consciousness  are  not  modes  of  motion.  If  they  were,  the  general 
theory  of  physics  would  compel  us  at  once  to  attempt  a  strict 
mathematical  correlation  between  physical  and  mental  phenomena. 
Just  as  the  momentum  of  masses  can  be  expressed,  with  a  tolerable 
approximation  to  exactness,  in  terms  of  heat  as  a  mode  of  motion, 
so  Avould  some  formula  be  conceivable  for  indicating  what  amount 
of  chemical  changes,  or  nerve-commotion,  in  the  matter  of  the 
brain,  is  the  mathematical  equivalent  of  the  conception  of  home,  of 
the  sense  of  obligation,  or  of  the  idea  of  God.  In  other  words,  it 
seems  impossible  to  regard  any  amount  of  physical  energy  as  ab- 
stracted from  the  bi'ain,  so  to  speak,  and  expended  or  stored  up  in 
consciousness.  Energy  is  stored  by  the  process  of  nutrition  in  the 
nervous  elements  of  the  brain  ;  it  becomes  kinetic  in  connection 
Avith  the  phenomena  of  consciousness.  But  between  the  mind, 
whether  regarded  as  merely  the  formal  subject  of  consciousness  or 
as  a  real  unit-being  whose  faculty  or  power  it  is  to  be  conscious, 
and  the  physical  basis  of  mind  in  the  brain,  no  correlation,  no  pass- 
ing back  and  forth  of  energy,  can  occur. 

Representing  the  same  truth  in  another  way,  we  may  declare : 
The  entire  circuit  of  the  transmission  and  distribution  of  energy  is 
complete  within  the  brain  itself.  Not  a  single  atom  enters  its  sub> 
stance  that  does  not  come  forth  unchanged,  with  all  its  forces  in- 
herent in  it.  No  atom  is  transferred  from  brain  to  mind,  as  all  the 
atoms  are  transferred  from  the  blood  to  the  nervous  substance  of 
the  brain.  Not  the  most  infinitesimal  amount  of  energy  exists, 
stored  in  the  constitution  of  the  molecules  of  this  substance,  which 


654  CONNECTION   OF   BRAIN   AND    MIND. 

is  not  eitlier  used  up  there  or  returned  to  external  nature  in  con- 
nection with  the  constitution  of  the  molecules  separated  from  this 
substance.  The  stricter  we  make  our  application  of  the  law  of  the 
correlation  and  conservation  of  energy  within  the  physical  realm, 
the  more  impossible  does  it  become  to  apply  it  at  all  to  the  rela- 
tions of  body  and  mind. 

§  15.  It  is  not  surprising  that,  in  the  estimate  of  one  who  is  un- 
accustomed to  regard  with  favor  any  explanation  of  phenomena 
which  does  not  come  under  the  most  general  law  of  all  phj^sics,  the 
case  of  the  mind  and  the  brain  should  seem  to  demand  the  most 
extraordinary  treatment.  In  any  event,  the  facts  of  consciousness, 
as  facts,  cannot  be  denied.  Whether  we  can  explain  them  or  not, 
with  or  without  use  of  the  law  of  the  conservation  and  correlation 
of  energy,  they  are  equally  plain  and  persistent.  Men  perceive, 
and  imagine,  and  remember,  and  reason,  and  believe  in  the  invisi- 
ble, and  choose,  etc.  AU  this  they  do,  as  possessed  C'f  a  body — 
and,  particularly,  of  a  nervous  mechanism,  the  activities  of  whose 
central  portion  are  related  in  some  special  and  unique  w^ay  with 
the  doing  of  all  this.  And  yet  sure,  beyond  doubt — it  is  argued — 
is  the  existence  of  the  atom,  with  its  host  of  inherent  energies  ; 
and  supreme  is  the  law  of  the  conservation  and  correlation  of  these 
energies  regarded  as  modifications  of  one  fundamental  form. 

In  view  of  so  grave  difficulties  it  has  been  of  late  customary  to 
escape  from  them  in  one  of  several  different  ways.  The  general 
claim  may  be  set  up  that  all  hopeful  inquiry  as  to  the  nature  of  real 
beings,  which  act  upon  and  are  acted  upon  by  each  other  under  the 
law  of  causation,  must  be  abandoned.  Knowledge,  it  is  said,  con- 
sists simply  in  the  relating  of  phenomena  under  certain  constant 
and  regular  forms  of  their  recurrence,  called  "laws,"  This  is  sub- 
stantially the  position  of  Positivism. 

It  may  also  be  held  that  all  mental  phenomena  are  to  be  re- 
garded as  merely  transitory  appearances — shadows  cast,  as  it  were, 
by  the  changing  activities  of  the  material  molecules  ;  and  that  the 
latter  are  the  only  realities.  In  this  case  the  constitution  and  ac- 
tivities of  the  molecules  are  all  to  be  regarded  as  determined  by 
the  interaction  of  the  ultimate  atoms  which  compose  them,  accord- 
ing to  their  inherent  and  inseparable  forces,  under  the  law  of  the 
conservation  and  correlation  of  2>hysical  energy.  Whenever  a  cer- 
tain constitution  and  consequent  modes  of  activity  are  brought 
about  in  the  molecules,  under  this  general  law,  then  it  is  of  their 
own  incomprehensible  nature  to  exhibit,  in  addition  to  the  various 
forms  of  motion  known  as  nerve-commotion,  another  peculiar  class 
of  coexisting  phenomena,  called    mental  phenomena.     The  latter 


MATEEIALISM   AND   MONISM.  65o 

phenomena  do  not  require  a  new  subject;  their  appearance  is  the 
necessary  result  simply  of  the  special  and  unique  constitution  and 
relations  of  the  physical  molecules  of  the  brain.  The  mental  phe- 
nomena are  one  form  of  expressing  the  fact  of  the  real  existence 
of  these  molecules,  with  such  a  constitution  and  in  such  relations. 
And  just  as  we  do  not  require  a  new  subject  for  the  mysterious 
and  unique  phenomena  of  magnetism,  or  of  crystallization,  but  be- 
lieve them  to  be  only  the  expression  of  the  new  relations  into  which 
the  same  subjects  of  all  phenomena — the  imperishable  atoms — 
have  been  brought  under  the  one  law  of  the  conservation  and  cor- 
relation of  energy  ;  just  so  do  we  find  no  particular  need  of  a 
new  kind  of  subject,  other  than  the  aggregated  atoms,  for  the  mys- 
terious and  unique  phenomena  of  consciousness.  This  position  is 
Materialism. 

Still  further,  the  impossibility  of  binding  together  by  a  causal 
tie,  under  the  law  of  the  conservation  and  correlation  of  energy, 
phenomena  so  utterly  incomparable  as  are  those  of  mind  and  brain, 
and  the  difficulty  of  assigning  the  mental  phenomena  to  the  same 
subject  as  that  which,  otherwise,  manifests  itself  only  as  modes  of 
motion  rather  than  modes  of  thought,  have  led  to  more  recondite 
speculation.  Hence  a  return  to- the  "mediaeval"  view  has  been 
made.  The  real  connection  of  mind  and  brain  has  been  found  in 
a  third  somewhat,  which  is  neither  mind  nor  brain,  as  we  know 
them,  but  is  the  ground  of  both.  There  is,  then — it  is  claimed — 
only  one  substance  as  the  real  subject  for  the  two  sets  of  proper- 
ties. "  The  one  substance,  with  two  sets  of  properties,  two  sides, 
the  physical  and  the  mental — a  double-faced  unity — would  appear 
to  comply  with  all  the  exigencies  of  the  case."  This  position  may, 
in  general,  be  designated  as  that  of  Monism. 

But  immediately  the  inquiry  arises  and  presses  for  an  answer, 
whether  we  may  not  know  something  as  to  the  real  nature  of  this 
"  double-faced  unity,"  besides  the  mere  fact  that,  phenomenally 
considered,  it  has  two  faces,  or  sides — the  physical  and  the  mental. 
Why  does  it  manifest  itself  both  as  physical  motion  and  as  mental 
states — one  Being,  in  two  utterly  incomparable  modes  of  manifes- 
tation? Is  it  itself  extended  and  movable,  a  material  reality?  or 
is  it  unextended  and  conscious,  a  psychical  reality?  To  refuse  to 
attempt  the  answer  to  this  question  is  to  take  refuge  in  Agnosti- 
cism— and  that  at  a  critical  point,  to  which  we  have  brought  our- 
selves unnecessarily  through  having  been  already  overwise.  For 
no  one  who  claims  already  to  know  enough  about  the  nature  of  so^ 
called  matter  and  of  so-called  mind  to  affirm  confidently  that  they 
cannot  be  two  forms  of  real  being,  acting  on  each  other  and  being 


656  CONNECTION   OF   BEAIN   AND   MIND. 

acted  npon  by  eacli  other,  is  entitled,  just  beyond  this  advanced 
line  of  knowledge,  to  make  a  run  sideways  into  the  refuge  of  con- 
fessed ignorance.  Furthermore,  if  the  "  double-faced  unity  "  is  held 
to  be,  in  reality,  either  matter  or  mind,  we  raise  again  all  the  diffi- 
culties as  to  a  real  connection  between  two  sets  of  phenomena  so 
incomparable.  Both  Materialistic  Monism  and  Idealistic  Monism 
have,  then,  to  undertake  the  task  of  showing  how  the  one  reality 
can  appear  under  these  two  phenomenal  forms  of  being — matter 
and  mind — with  its  two  sides  causally  connected. 

§  16.  So  far  as  the  theories,  which  are  proposed  in  order  to  escape 
the  difficulty  of  admitting  a  direct  causal  connection  between  mind 
and  brain,  involve  the  assumption  that  the  phenomena  of  conscious- 
ness can  be  regarded  as  modes  of  motion,  or  can  be  attributed  to 
the  molecules  of  the  brain  as  their  sole  subject,  they  have  already 
been  refuted.  So  far  as  these  theories  resolve  themselves  into  the 
speculations  joroposed  by  different  schools  of  philosophy  concerning 
the  supreme  philosophical  inquiry.  What  is  the  nature  of  the  Ulti- 
mate Reality  (the  Absolute)?  psycho-physical  researches  have  no 
direct  answer  to  offer  to  them.  But  our  present  inquiry  is  a  more 
modest  one,  namely  :  What  is  the  nature  of  the  real  connection 
between  human  mind  and  human  brain,  so  far  as  psycho-physical 
science  throws  any  light  on  such  connection  ?  Our  general  reply 
is  :  This  connection  is,  in  reality,  such  as  we  find  between  all  so- 
called  real  beings,  to  whichever  of  the  two  supreme  classes  (material 
or  spiritual)  such  beings  may  belong.  The  molecules  of  the  brain 
(so  far,  at  least,  as  psj'cho-physical  science  knows  anything  of  them) 
are  composed  of  elements  of  material  reality,  called  "atoms  ; "  these 
atoms  act  by  way  of  motion,  according  to  their  constitution  and  re- 
lations to  each  other  and  to  their  environment.  The  mind,  on  the 
other  hand,  is  a  real  unit-being  of  another  order  than  that  of  the 
atoms.  Its  acts  are  the  various  modes  or  states  of  consciousness. 
This  being  called  mind  is  causally  related  to  the  beings  called 
atoms ;  the  relation  is  mutual.  The  mind  behaves  as  it  does  be- 
have because  of  the  constitution  and  behavior  of  the  molecules  of 
the  brain.  The  molecules  of  the  brain  behave  as  they  do  behave 
because  of  the  nature  and  activities  of  the  mind.  Each  acts  in  view 
of  the  other.  The  action  of  each  accounts  for  the  action  of  the 
other.  But  the  action  of  neither  is  to  be  explained  as  solety  due  to 
the  action  of  the  other ;  neither  mind  nor  brain  can  be  regarded  as 
the  subject  for  the  phenomena  ordinarily  ascribed  to  the  other. 

The  position  just  taken  is,  of  course,  the  most  unmistakable 
Dualism.  It  assumes  two  kinds  of  real  beings  for  the  two  incom- 
parable classes  of  phenomena.     Whether  this  position  is  the  ulti- 


THE   VIEW   OF  DUALISM.  657 

mate  one  attainable  by  bunian  reason  or  not,  tlie  facts  of  Plij'siolog- 
ical  Psychology  afford  no  basis  for  speculation.  It  is  possible  that 
some  higher  point  of  view  might  enable  us  to  resolve  the  Dualism, 
and  to  discover  a  common  ground  for  the  body  and  soul  of  man,  and 
even  for  all  physical  and  spiritual  phenomena.  But  psycho  phj'sical 
science,  simply  observing  the  facts  and  building  upon  them,  and 
upon  such  assumptions  as  it,  in  common  with  all  the  sciences^  is 
compelled  to  make,  establishes  this  Dualism  of  brain  and  mind,  and 
then  hands  the  case  over  to  philosophy  for  further  consideration. 
Moreover,  there  is  nothing  in  any  science,  physical  or  psychological, 
which  offers  a  single  valid  reason  why  both  mind  and  brain  should 
not  be  regarded  as  real  beings,  material  and  spiritual,  mutually  in- 
teracting. This  last  statement  we  shall  now  justify  by  considering, 
briefly,  the  objections  to  it,  which  have  induced  the  resort  to  the 
before-mentioned  other  theories. 

§  17.  The  law  of  the  conservation  and  correlation  of  energy — as 
far  as  it  has  been  observed,  or  can  reasonably  be  assumed  to  hold 
good — offers  no  valid  objection  to  the  existence  of  a  real  causal 
connection  between  the  mind  and  the  brain.  The  present  position 
of  this  law  is  that  of  an  empirical  generalization,  found  to  hold  ap- 
proximatel}'  true  for  a  large  number  of  classes  of  phenomena,  and 
presumably  true  for  yet  other  classes.  To  exalt  it  to  the  place  of  a 
universal  and  necessary  relation  among  all  phenomena  of  every  class 
— mental  as  well  as  physical — would  be  unwarrantably  to  extend 
its  application.  Even  in  the  sphere  of  physical  events  the  law  is  as 
yet  demonstrably  true  only  to  a  limited  extent.  The  various  forms 
of  physical  energy  in  the  inorganic  world  are  as  yet  by  no  means 
all  reducible  to  the  terms  of  this  law.  Gravitation,  on  the  one 
hand,  and  magnetism,  or  chemical  affinity,  or  cohesion,  or  the  forces 
that  act  when  every  crj-stal  is  formed,  on  the  other  hand,  cannot  be 
as  yet  related  together  so  as  to  be  expressed  in  these  terms.  No 
mathematical  formula,  or  picture  framed  by  the  imagination,  has 
thus  far  bridged  over  the  gap  between  the  molecular  energy  of 
inorganic  and  that  of  organic  structures.  In  discussing  the  phe- 
nomena of  general  nerve-j^bysiology,  it  was  made  obvious  at  every 
turn  that  even  the  behavior  of  the  vital  nerve-muscle  machine 
under  the  influence  of  electrical  or  other  excitation  cannot  be  ac- 
counted for  by  any  conceivable  application  of  the  known  laws  of 
those  forces  that  move  unorganized  particles  of  matter.  Nerve- 
force — what  it  is  and  what  it  will  do  ;  what  it  is  as  judged  by  what 
it  will  do — cannot,  at  present,  be  correlated  Avith  any  of  the  forms 
of  energy  which  act  as  nervous  stimuli.  Yet  who  would  for  a 
moment  hesitate  to  say  that  the  action  of  the  electrical  current,  or 
42 


658  coNNECTioisr  or  BRAiisr  and  mind. 

of  the  irritating  acid,  or  of  mechanical  impulse  when  applied  to 
the  nerve,  is  a  "■came"  of  the  contraction  of  the  muscle? 

The  effort  of  certain  scientific  observers  to  bring  aU  causal  rela- 
tion, all  action  of  one  being  on  another,  under  the  law  of  the  con- 
servation and  correlation  of  physical  energy  is  mistaken,  and  must 
prove  unsuccessful.  The  discovery  that  all  the  action  of  physical 
beings  is  to  be  understood  only  in  terms  of  motion,  and  that  all  re- 
lations of  such  beings  are  to  be  expressed  as  comparable  quantities 
of  motion,  either  obvious  or  potential,  has,  of  course,  greatly  stim- 
ulated this  effort.  The  effort  is  to  a  certain  extent  laudable.  It 
has  unified  the  physical  universe  ;  it  has  showed  to  us  this  universe 
all  alive,  as  it  were,  with  unceasing,  correlated,  wondrous  motions, 
which  it  is  indeed  conceivable  should  be  all  commensurable  one 
with  another.  But  it  should  never  be  forgotten  that  this  picture 
of  an  objective  world  composed  of  beings  called  atoms,  eternally 
moving  with  reference  to  each  other  and  according  to  the  law  of 
the  conservation  and  correlation  of  energy,  is  itself  a  picture  con- 
structed by  the  imaging  and  reasoning  mind.  As  such  a  mental 
picture,  it  is,  and  must  always  remain,  dependent  on  the  imagina- 
tion. Mind,  as  reasoning  and  imagining,  follows  the  moving 
beings  into  minutiae  of  forms  and  into  places  where  observation 
can  never  reach  them.  Hence  the  talk  of  atoms  having  "forces 
inherent"  in  them,  of  energy  "potential"  as  well  as  kinetic,  of  the 
"influence"  or  "action"  of  molecule  on  molecule,  and  mass  on 
mass,  under  this  one  great  law  discovered  by  modern  physics. 

For  the  principle  of  causation  is  of  far  wider  application,  and  of 
far  more  secure  foundation,  than  the  law  of  the  conservation  and 
correlation  of  energy.  The  one  is  a  law  which,  in  the  form  of  the 
principle  of  reason  and  consequent,  is  Avorked  into  the  very  struct- 
ure of  the  mind,  and  is  of  universal  and  necessary  application  to  all 
phenomena  ;  the  other  is  an  empirical  generalization,  of  doubtful 
import  and  uncertain  extent  of  application.  Indeed,  we  should  not 
accept  the  phj'sical  law  at  all,  or  seek  to  establish  its  further  appli- 
cation, were  it  not  that  the  mental  principle  is  already  taken  for 
granted.  It  is  in  our  search  for  causes,  and  as  a  result  of  our  per- 
suasion that  real  beings  exist,  which  act  on  and  are  acted  on  by  each 
other,  that  we  hit  upon  tlie  hypothesis  of  the  sum-total  of  their  ener- 
gies as  shown  by  motion  remaining  unchanged,  and  of  its  different 
kinds  being  all  measurable  one  against  the  other.  But  no  objection 
exists,  either  in  the  nature  of  the  mind  or  in  the  nature  of  things,  so 
far  as  we  know,  to  the  reverse  of  this  being  true.  For  example,  a 
world  might  be  constructed  in  which  a  certain  number  of  physical 
beings,  of  a  certain  kind  (molecules  and  masses),  remained  abso« 


NATURE   OF   THE   CAUSAL  ISTEXUS.  659 

lutely  motionless  and  unchanged,  while  all  other  beings  were  in 
perpetual  motion.  Or  a  world  might  be  constructed  in  which  the 
activities  of  different  physical  beings,  as  expressed  by  motion,  should 
be  related  in  a  totally  different  way  from  that  formulated  by  the 
present  law  of  the  conservation  and  correlation  of  energy.  In  this 
imaginary  world,  some  kinds  of  beings  might  put  forth  an  amount 
of  energy  which  was  proportional  to  that  of  all  the  energy  of  the 
beings  acting  on  them,  as  the  square  to  the  square-root,  or  as  the 
cube  to  the  cube-root ;  and  other  kinds  of  beings  might  act  and  be 
acted  upou  under  very  different  laws  of  relation  with  resj)ect  to  the 
quantity  of  energy.  In  fine,  the  fact  that  the  law  of  the  conserva- 
tion and  correlation  of  energy  caunot  hold  true  as  to  the  connection 
between  physical  and  psychical  phenomena  furnishes  no  sort  of 
proof  against  the  reality  of  the  mind  or  of  the  causal  connection 
between  it  and  the  brain. 

§  18.  Nor  is  there  anything  in  the  nature  of  the  so-called  "cau- 
sal nexus  "  itself  which  forms  a  reason  why  it  should  not  be  as- 
sumed to  exist  between  brain  and  mind.  For  what  do  we  mean 
when  we  speak  of  one  thing  or  event  as  the  cause  of  another? 
"What  do  we  mean  when  we  speak  of  "influence  exerted,"  "force 
transmitted  "  or  "  passing  over  "  from  one  being  to  another,  etc.  ? 
Nothing  that  can  be  explained  or  illustrated  after  the  analogy  of 
any  series  or  collocation  of  phenomena,  of  any  relation  of  one  ob- 
ject to  another  as  discernible  by  sense  or  picturable  by  imagination. 
Nothing  passes  from  the  match  to  the  gunpowder  which  explains 
why  the  latter  explodes  ;  or  from  the  bat  to  the  ball  which  explains 
why  the  latter,  when  struck  by  the  former,  changes  the  direction  of 
its  motion.  The  proximity  of  the  earth  and  the  unsupported  con- 
dition of  the  apple,  shaken  by  the  wind  from  its  stem,  are  indeed 
spoken  of  as  the  cause  of  the  apple's  fall ;  but  no  invisible  hands 
are  reached  up  from  the  ground  to  draw  the  apple  down.  Were 
such  feelers  put  out  to  clasp  the  smaller  body  and  draw  it  to  the 
larger,  the  energy  of  the  clasp  and  its  effect  would  still  as  truly 
need  an  explanation  as  does  the  action  of  the  so-called  force  of 
gravitation.  None  of  the  senses  is  capable  of  discovering  or  ap- 
preciating the  energy  that  is  assumed  to  act ;  the  causes  of  an  event 
cannot  be  seen,  handled,  heard,  smelled,  or  tasted.  The  w^orld  of 
experience  given  to  us  by  the  activity  of  the  senses  is  a  world  in 
which  a  ceaseless  change  of  objects  takes  place,  but  any  evidence 
of  a  tie  connecting  the  physical  phenomena  with  real  beings  as 
their  attributes,  or  connecting  our  minds  with  these  physical  real 
beings,  so  that  they  may  be  said  to  affect  us,  is  quite  beyond  the 
range  of  the  senses. 


660  cojS^jS'ECTION'  of  braij^  and  mind. 

In  general,  it  may  be  said  that  the  world  of  appearances  is  found 
by  an  anaij^sis  of  our  adult  experience  to  be  assumed  to  rest,  as  it 
were,  upon  an  invisible  Avorld  of  reality.  The  popular  and  uncriti- 
cal mode  of  the  assumption  is,  that  the  world  is  made  up  of  a  great 
number  of  real  "  Things  ; "  that  these  things  exist  ex-^j'a-mentally, 
just  as  they  appear  to  us  as  objects  of  experience  ;  that  our  knowl- 
edge of  them  is  a  more  or  less  true  copy,  obtained  through  the 
senses,  of  what  they  extra-mentally  are  ;  and  that  these  things  are 
constantly  doing  somewhat  to  each  other — acting  on  each  other  and 
being  acted  on  by  each  other.  Scientific  researches  greatly  modify 
the  character  of  the  j^opular  assumption.  They  show  that  it  is  de- 
monstrably false  in  almost  every  particular  ;  and  yet  they  re-estab- 
hsh  it  in  other  forms.  Physics,  by  a  series  of  careful  observations 
and  subtle  and  remote  inferences,  constructs  an  extra-mental  world 
of  moving  atoms  ;  it  shows  us  how  these  atoms  always  have  regard 
to  each  other  when  they  move,  and  are  ceaselessly  moving  with 
reference  to  each  other ;  it  strives  to  image  the  direction  and  veloc- 
ity of  the  most  infinitesimal  of  these  motions,  and  to  formulate 
their  laws  or  constant  modes  of  relation.  Psychology  shows  how 
the  world  of  mental  objects,  the  only  world  of  immediate  experi- 
ences, is  built  up  by  the  synthetic  activity  of  mind  ;  it  calls  upon 
the  physicist  to  remember  that  he  has  no  other  way  of  reaching 
these  atoms,  and  of  discovering  the  laws  of  their  relations,  except 
by  the  path  of  mental  activity  ;  and  it  reminds  him  that  this  activity 
cannot  escape  the  control  of  mental  law.  But  both  the  popular 
view  and  the  scientific  attainment  are  in  substantial  agreement  as 
to  their  fundamental  view  of  the  world.  Both  believe  that  our  ex- 
jjerience  is  exj)licable  only  on  the  general  hypothesis  of  the  exist- 
ence of  a  vast  number  of  real  beings  Avhich  perpetually  act  on  each 
other  and  are  acted  upon  by  each  other. 

§  19.  The  effort  to  restrict  the  working  of  the  above-mentioned 
assumption,  in  which  common-sense  and  scientific  analysis  both 
agree,  just  at  the  point  w'here  the  relation  of  mind  and  brain  is 
subjected  to  scientific  treatment,  is  as  needless  as  it  is  unavailing. 
Because  it  is  both  needless  and  unavailing  it  is  often  absuril.  If  it 
be  granted  that  the  law  of  the  conservation  and  correlation  of  ph^-s- 
ical  energy  cannot  possibly  be  applicable  to  the  connection  of  mind 
and  brain,  and  yet  that  all  which  we  know  of  the  nature  and  extent 
of  this  law  forms  no  valid  objection  to  regarding  both  mind  and 
material  atoms  as  real  beings  standing  in  certain  relations  to  each 
othei' — What  good  reason  can  be  urged  for  refusing  to  affirm  a  causal 
connection  between  the  two?  The  fear  that  either  of  the  two  parties 
will  suffer  in  dignity  or  integrity  by  such  connection  Avith  the  othei 


CAUSAL   INFLUElSrCE   OF   THE   BIlAIlvr.  661 

may  easily  be  laid  to  rest ;  and  if  it  could  not  be,  it  would  have  no 
right  to  interfere  with  the  only  reasonable  interpretation  of  psycho- 
physical facts.  Beings  do  not  lose  their  reality,  or  characteristic 
natiu'e,  or  value  in  the  universe  of  Being,  because  they  are  causally 
connected  with  other  beings.  On  the  contraiy,  none  but  real  be- 
ings can  be  thus  connected  with  each  other  ;  none  but  real  beings 
can  act  and  be  acted  upon.  The  so-called  causal  connection  is  no 
bondage  of  such  nature  as  to  destroy  the  nature  of  the  beings  which 
act  under  it.  Only  beings  that  have  natures  of  their  own  can  be 
causally  connected.  In,  other  words,  all  that  apjDcars  to  us  as  a 
causal  relation  between  the  objects  of  our  experience  is,  ultimately 
considered,  due  to  no  material  spur  or  whip  which  urges,  or  band 
that  represses,  as  though  one  kind  of  real  being  could  thus  domi- 
nate and  subdue  another.  No  atom  acts  without  being  acted  on  ; 
what  it  does  depends  both  upon  what  it  is  and  also  upon  how  it 
stands  related  to  other  atoms. 

§  20.  We  affirm,  then,  that  we  are  entitled  to  say  :  The  changes 
of  the  brain  are  a  cause  of  the  states  of  consciousness  ;  and  the 
mind  behaves  as  it  does  behave,  because  of  the  behavior  of  the 
molecules  of  the  brain.  Modify  the  constitution  and  functional 
activity  of  the  material  atoms,  and  you  make  the  activities  of  the 
mind,  its  acts  and  states  of  consciousness,  to  be  differently  j)ut 
forth  by  the  mind.  The  nature  and  extent  of  this  "  influence  "  of 
the  material  basis  upon  the  psychical  subject  can  never  be  deter- 
mined a  priori,  or  brought  under  any  general  formula  applicable 
only  to  a  restricted  sphere  of  physical  action,  like  the  law  of  the 
conservation  and  correlation  of  physical  energy.  The  nature  and 
extent  of  such  influence  must  be  learned  by  investigation.  It  has 
been  the  special  task  of  this  treatise  on  Physiological  Psychology 
to  investigate  and,  as  far  as  possible,  to  formulate  the  causal  action 
of  brain  on  mind.  Such  action  has  been  seen  to  consist  chiefly 
(if  not  whoU}-)  in  determining  the  intensity,  quality,  mode  of  com- 
bination, and  of  recurrence  in  time,  of  the  sensational  elements  of 
the  mind's  activity,  and  of  its  other  activities  so  far  as  dependent 
upon  the  sensational  elements. 

The  affirmation  of  a  causal  influence  of  the  brain  on  the  mind, 
however,  does  not  really  work  any  prejudice  to  the  claims  of  the 
mind  to  be  considered  a  real  being,  or  to  be  spiritual  and  free.  For 
the  sole  account  or  cause  of  the  mind's  activities  can,  in  no  instance, 
be  found  in  the  molecular  condition  and  changes  of  the  brain. 
The  simplest  sensation  must  be  referred  also  to  the  nature  of  the 
mind  as  its  cause.  It  must  be  considered,  not  simply  as  caused  by 
a  certain  form  of  nerve-commotion  in  the  cerebral  cortex,  but  also 


662  coNNECTioisr  or  beaijst  and  mind. 

as  a  psychical  activity  put  forth  by  the  being  called  mind.  There 
is  no  incompatibility  in  these  two  ways  of  regarding  each  state  of 
sensation.  Even  in  the  case  of  some  physical  event,  the  nature  of 
each  of  the  factors  combining  to  form  the  event  must  be  taken 
into  the  account.  For  example,  atoms  of  oxygen  will,  under  cer- 
tain circumstances,  unite  with  atoms  of  hydrogen  to  form  water  ; 
under  other  circumstances  they  will  unite  with  atoms  of  iron  to 
form  iron-rust  ;  they  may  also  be  mechanically  mixed  with  nitro- 
gen-atoms to  form  air,  etc.  In  each  case  the  cause  of  the  result  is 
to  be  found  in  the  presence  with  the  oxygen,  under  certain  definite 
circumstances,  of  atoms  of  hydrogen,  iron,  nitrogen,  etc.  But  in 
each  case  the  cause  is  also  equally  to  be  found  in  the  nature  of 
the  atom  of  oxygen.  So  every  sensation,  however  closely  it  may 
be  correlated  with  the  condition  and  functional  activity  of  the 
molecules  of  the  brain,  must  be  explained  by  referring  it  to  the 
nature  of  the  mind  which  has  the  sensation.  Nothing  which  Physi- 
ological Psychology  has  ever  discovered,  or  can  hope  to  discover, 
in  the  least  mitigates  the  necessity  of  saying,  when  the  question 
is  asked — AVhy  does  the  mind  behave  in  this  particular  way  under 
such  circumstances  ?^It  is  the  nature  of  the  mind  so  to  behave 
when  its  circumstances  are  such.  In  other  words,  our  explanations 
of  the  causes  of  mental  phenomena,  as  lying  in  the  physical  basis 
of  such  phenomena,  does  not  at  all  satisfy  the  need  of  a  real  and 
spiritual  subject  of  the  phenomena. 

Moreover,  we  have  seen  that  there  are  large  and  most  important 
classes  of  mental  activities  which  can  scarcely  be  conceived  of  as 
standing  in  any  direct  relation  to  the  nerve-commotions  of  the 
cerebral  cortex.  These  classics  are  indeed  always  allied  with  phe- 
nomena of  sensation  and  feeling  for  which  we  can  trace  a  bodily 
basis.  But  this  fact  only  makes  their  connection  with  the  brain 
presumably  more  indirect.  For  the  explanation  of  such  classes  of 
mental  phenomena  we  are  driven  much  more  imperatively  and  ex- 
clusively to  an  appeal  to  the  existence  of  a  spiritual  subject,  with  a 
nature  and  laws  of  action  very  different  from  those  ascribed  to  its 
physical  basis,  the  brain. 

§  21.  We  affirm,  also,  that  we  are  equally  entitled  to  say  :  The 
states  of  consciousness  are  a  cause  of  the  molecular  condition  and 
changes  of  the  nervous  mass  of  the  brain,  and  through  it  of  the 
other  tissues  and  organs  of  the  body.  And  just  as  no  fear  for  the 
reality,  integrity,  and  dignity  of  the  mind  prevents  us  from  accept- 
ing its  dependence  for  the  mode  of  its  activity  upon  the  condition 
of  the  brain,  so  no  fear  for  the  reality  of  physical  substance,  and 
for  the  value  and  extension  of  physical  law,  pi*events  us  from  aa 


•  CAUSAL   USTFLUENCE   OF   MIND.  6Qo 

serting  the  dependence  of  the  brain,  for  the  mode  of  its  activit}-, 
upon  the  states  of  the  mind.  Of  course — it  need  scarcely  be  said 
again — no  relation  exists  between  these  two  kinds  of  beings  which 
can  be  represented  as  an  interchange  of  physical  energy,  under 
the  law  of  the  conservation  and  correlation  of  such  energy.  This 
fact,  however,  affords  no  objection  to  our  recognizing  a  true  causal 
counectiou  between  the  two,  unless  we  are  ready  to  insist  upon 
the  monstrous  claim  that  modern  physical  science  is  entitled  to 
affirm  the  impossibility  of  any  interaction  (or  conditional  action) 
taking  place  in  the  universe  otherwise  than  between  material  atoms 
under  the  aforesaid  law. 

The  phenomena  which  indicate  that  mind  operates  as  true  cause 
within  the  structure  of  the  body  are  innumerable.  They  are  quite 
as  numerous,  though  perhaps  not  so  obvious  and  impressive,  as 
those  which  indicate  the  reverse  relation.  The  chief  reason  why 
these  phenomena  are  relatively  little  regarded  in  psycho-physical 
researches  is,  that  the  real  causes  are  in  this  case  not  readily  made 
the  objects  of  observation  and  measurement.  External  stimuli  con- 
stitute the  causes  of  mental  changes  which  we  can  most  easily  ob- 
serve and  estimate.  Ideas,  feeling,  and  acts  of  will  arising  in  the 
consciousness,  and  considered  as  causes  of  the  resulting  bodily 
changes,  cannot  be  treated  by  the  same  methods  of  experimental 
science  as  apply  to  the  physical  stimuli.  But  that  the  mind  acts 
on  the  body  is  one  of  the  most  familiar  of  experiences.  Such  ac- 
tion penetrates  and  modifies  all  the  Hfe  of  the  body.  Hence  the 
material  mechanism  of  the  animal  structure  can  never  be  consid- 
ered, with  a  view  to  explain  what  is  going  on  within  it,  as  though 
it  were  disconnected  from  the  consciousness  of  the  animal.  The 
most  purely  vegetative  of  the  processes  of  the  human  body  are  de- 
pendent for  their  character  upon  the  states  of  the  human  mind. 
The  nutrition  of  the  tissues,  the  circulation  of  the  blood,  the  secre- 
tion of  different  kinds  of  fluids,  the  healthy  or  diseased  nature  of 
the  vital  processes,  are  dependent  upon  the  states  of  the  mind.  If 
abnormal  digestion  produces  melancholy,  it  is  equally  true  that 
melancholy  causes  bad  digestion.  In  the  case  of  the  rise  of  strong 
emotions,  like  anger  or  grief,  the  increasing  affection  of  the  mind 
builds  itself  up  upon  a  physical  basis  of  increasing  disturbance  of 
the  organs  ;  but  it  is  equally  obvious  that  the  starting  of  the  emo- 
tion in  consciousness,  and  the  letting  of  it  slip  from  control,  are 
necessarily  followed  by  gathering  momentum  to  the  organic  dis- 
turbance. Irregular  action  of  the  heart,  caused  by  organic  defect 
or  weakness,  occasions  a  feeling  of  indescribable  alarm  in  the  soul ; 
fear  is  followed,  through  the  action  of  the  mind  upon  the  nervous 


064  coisrisrECTioN'  of  brain  and  mind. 

centres,  by  functional  incapacity  of  the  heart.  The  impure  condi- 
tion of  the  arterial  blood  which  is  characteristic  of  certain  diseases 
brings  about  a  chronic  state  of  mental  lassitude  or  anxiety  ;  care, 
chagrin,  and  ennui  poison  the  arterial  blood.  The  lesion  of  the 
cortical  substance  produced  by  a  growing  abscess  or  broken  blood- 
vessel impairs  the  mind's  powers  of  sensation  and  thought ;  ex- 
cessive thought  and  over-excited  feeling  wear  away  the  brain. 

The  entire  class  of  phenomena  which  we  are  entitled  to  call 
"  voluntary,"  in  the  widest  sense  of  the  word,  might  be  appealed 
to  in  jDroof  of  the  same  principle.  Whether  they  show  that  the 
mind  is  "  free,"  in  the  highest  ethical  meaning  of  the  word,  or  not 
(and  upon  this  question  psycho-physical  science  cannot  pronounce), 
they  certainly  do  show  that  the  condition  of  the  bodily  organs  is 
made  dependent,  through  the  nervous  elements  of  the  brain,  upon 
the  states  of  the  mind.  And  here  are,  in  point,  the  phenomena  of 
the  voluntary  innervation  of  the  organ  by  fixing  the  attention,  of  the 
dependence  of  reaction-time  upon  the  exercise  of  the  will  through 
attention  of  the  person  reacting,  of  the  abstraction  of  regard  from 
the  images  of  sense  when  occupied  in  reflective  thought,  as  well 
as  all  the  more  marvellous  instances  of  self-control  in  determining 
the  results  of  disease,  etc. 

The  elevation  of  the  bodily  activities  to  the  most  astonishing 
precision,  under  the  influence  of  high  and  strong  artistic  feeling, 
or  sense  of  duty,  is  also  a  noteworthy  fact  of  the  same  order.  The 
mind  has  not  the  poAver  to  constitute,  in  opposition  to  fixed  chem- 
ical affinities,  a  single  molecule,  or  to  execute  the  slightest  move- 
ment of  a  single  muscle,  without  involving  the  nervous  system  in 
the  expenditure  of  the  requisite  energy.  Moreover,  this  energy 
must  be  started  in  the  appropriate  cortical  area  and  descend  along 
the  allotted  motor  tracts.  We  cannot  explain  how  it  is  that  mole- 
cules of  nervous  matter  can  be  acted  upon  in  view  of  'states  of 
consciousness.  But  neither  can  we  explain  how  one  kind  of  atoms 
comes  to  act  as  it  does  in  view  of  the  presence  and  action  of  atoms 
of  another  kind.  Nevertheless,  we  can  just  as  little  assume  to  ex- 
plain away  the  fact  of  such  obvious  causal  connection,  because  we 
cannot  bring  the  measure  of  the  connection  under  the  same  law  as 
that  which  maintains  itself  among  certain  modes  of  physical  mo- 
tion. 

§  22.  No  valid  objection,  therefore,  can  be  urged  against  con- 
ceiving of  the  connection  between  mind  and  brain  in  the  following 
way,  at  once  most  natural  and  most  philosophical :  The  brain  is  a 
vast  collection  of  material  molecules,  whose  constitution  and  ar- 
rangement are  such  as  to  connect  them,  in  a  unique  way,  with  cer- 


'     CAUSAL   INFLUENCE   OF   MIND.  665 

tain  forms  of  physical  energy  outside  of  the  body.  Whenever  these 
appropriate  forms  of  energy  act  upon  the  parts  of  the  nervous  sys- 
tem lying  below,  and  the  impulses  are  transmitted  to  the  brain, 
or  whenever  the  chemical  character  of  its  blood-supply  is  altered, 
then  the  molecules  of  the  brain  are  capable  of  undergoing  very  re- 
markable and  intricate  changes  of  constitution  and  arrangement. 
That  is,  the  brain  can  be  stimulated  to  certain  of  its  peculiar  com- 
binations of  nerve-commotion  by  external  stimuli.  Moreover,  it  is 
constantly  initiating  other  combinations  of  nei've-commotion  that 
are  apparently  not  due  to  such  stimuli.  Some  of  its  actions,  that 
is,  are  of  a  kind  constantly  arising  within  the  system  itself  ;  they  are 
called  automatic.  We  have  as  yet  no  adequate  means  whatever 
for  making  a  quantitative  statement  of  the  relations  which  exist 
between  the  energy  of  atoms  thus  constituted  and  arranged  and 
the  energy  of  the  masses  or  molecules  that  serve  as  stimuli  of  the 
system  composed  of  these  atoms.  Nervous  energy  is  not  an  entity 
to  be  dealt  with  by  a  sum  in  addition  and  subtraction  of  momenta. 
For  aught  we  know,  it  is  of  the  nature  of  atoms,  when  they  are 
brought  into  relations  so  extraordinary  as  those  which  prevail  in 
the  nervous  system,  to  behave  with  reference  to  each  other  in  a 
way  that  is  wholly  irreducible  to  any  simple  formula  like  that  of 
the  conservation  and  correlation  of  energy.  If  this  should  final- 
ly appear  to  be  indubitably  true,  the  fact  would  not  be  specially 
mysterious.  All  action  and  reaction  of  the  atoms  is  mysterious  ; 
the  methods  of  it  are  to  be  learned  from  experience  as  ultimate 
and  inexplicable  facts. 

Still  further,  the  molecules  of  the  brain  are  so  constituted  and 
arranged  as  to  be  capable  of  standing  in  yet  more  surprising  and 
unique  relations  to  a  being  of  a  different  nature  from  their  own — 
that  is,  to  the  mind.  These  relations  involve  a  causal  connection  as 
truly  as  any  relations  of  real  physical  beings  in  which  such  beings, 
as  we  are  compelled  to  believe,  act  on  each  other  and  are  acted  on 
by  each  other.  That  molecules  thus  constituted  and  arranged  are 
causally  connected  with  the  subject  of  consciousness  is  an  ultimate 
fact  ;  it  involves  the  nature  of  both  classes  of  beings  thus  connected 
— of  the  brain  and  of  the  mind  ;  it  involves  also  the  action  of  each 
upon  the  other.  In  speaking,  however,  of  mind  and  brain  as  act- 
ing on  each  other,  we  accomplish  nothing  whatever  for  the  comple- 
tion of  the  picture  by  trying  to  introduce  the  conception  of  ener- 
gy " transmitted  "  or  "passed  over"  from  one  to  the  other.  The 
simple,  ultimate  fact  remains,  that  how  each  behaves  depends  upon 
the  behavior  of  the  other.  It  is  the  business  of  psycho-physical 
science  to  discover,  if  possible,  the  general  modes  of  this  depend- 


666  CONNECTION   OF   BRAIN   AND   MIND. 

eBce — that  is,  the  laws  of  the  relation  between  the  mind  and  the 
brain. 

§  23.  In  more  particular  description  of  the  connection  between 
the  mind  and  the  brain,  it  may  be  said  that  all  intercourse  between 
material  objects  and  the  spiritual  subject  involves  three  processes 
— a  physical,  a  physiological,  and  a  psychical.  In  these  processes 
the  perceived  object  and  the  perceiving  subject  mutually  condition 
each  other.  This  fact,  however,  does  not  destroy  the  necessitj^ 
under  which  all  scientific  investigation  finds  itself,  of  assuming  that 
both  object  and  subject  exist  as  real  beings.  The  physical  pro- 
cess consists  in  the  action  of  the  appropriate  modes  of  physical 
energy  upon  the  nervous  end-apparatus  of  sense.  The  bringing  of 
such  modes  of  energy  to  bear  upon  the  apparatus  is  accomplished 
through  mechanical  contrivances — such  as  the  means  for  forming 
an  image  on  the  retina  in  the  eye,  and  for  conveying  the  modified 
acoustic  impulses  to  the  organ  of  Corti  in  the  ear. 

The  second  process  consists  in  transmuting  the  physical  ener- 
gies, in  part  at  least,  into  a  physiological  process,  a  nerve-com- 
motion within  the  nervous  system  ;  and  in  propagating  such  nerve- 
commotion  along  the  proper  tracts  and  diffusing  it  over  the  various 
areas  of  this  system.  Inasmuch  as  the  physiological  process  is 
also  a  physical  process — that  is,  a  mode  of  the  motion  of  mate- 
rial molecules,  accompanied  by  chemical  and  electrical  and  other 
changes — it  must  be  conceived  of  as  standing  in  certain  relations 
of  quality  and  quantity  to  the  first,  or  more  distinctively  j)hysical, 
process.  But  that  the  law  of  the  conservation  and  correlation  of 
energy,  as  formulated  for  much  simpler  cases  of  the  relations  of 
forces  between  inorganic  bodies,  applies  to  the  relations  of  the 
nervous  system  and  its  stimuli,  or  within  the  different  parts  of  the 
nervous  system  itself,  we  are  not  yet  able  to  affirm  with  confi- 
dence. 

The  third  process  is  psychical ;  it  is  a  process  which  is  a  psychi- 
cal event,  a  forth-putting  of  the  energy  of  mind.  It  is  directly 
correlated  with  the  physiological  process  only  when  the  latter  has 
been  realized  in  certain  cerebral  areas.  It  is  not  to  be  explained 
as  a  resultant  of  the  cerebral  physiological  process,  but  as  an  ac- 
tion of  the  mind  which  is  conditioned  upon  that  process.  So,  also, 
are  we  entitled  to  say  that,  when  certain  psychical  processes,  by 
way  of  feeling,  ideation,  and  volition,  take  place,  then,  and  as  con- 
ditioned upon  these  processes,  certain  corresponding  physiological 
processes  occur  in  the  brain  ;  the  physiological  processes,  being 
propagated  from  the  central  nervous  system,  end  in  physical  pro- 
cesses returning  energy  to  the  world  outside  of  the  body. 


MIND   A   REAL    BEING.  667 

When  the  mental  process  is  a  perception  of  some  object,  called 
an  "  external "'  object,  it  is  no  less  truly  a  psychical  process.  The 
mind  creates  its  own  objects  ;  presents  itself  with  its  own  presen- 
tations of  sense  ;  acts  to  bring  forth  that  which  it  knows  as  not 
itself.  But  it  does  all  this  as  dependent  upon  the  processes  which 
take  place  outside  of  itself,  and  with  the  assumption  of  extra-men- 
tid  realities  as  existing,  to  which  it  stands  in  the  relation  of  cause 
and  effect. 

§  24.  Finally,  then,  the  assumption  that  the  mind  is  a  real  being, 
which  can  be  acted  upon  by  the  brain,  and  which  can  act  on  the  body 
through  the  brain,  is  the  only  one  compatible  with  all  the  facts  of  ex- 
perience. There  is  nothing  which  we  know  about  the  nature  of 
material  beings  and  the  laws  of  their  relation  to  each  other,  or 
about  the  nature  of  spiritual  beings  and  their  possible  relation  to 
material  beings,  or  about  the  nature  of  causal  eflficiency  whether 
in  the  form  of  so-called  physical  energy  or  in  that  of  activity  in 
consciousness,  Avhich  forbids  the  aforesaid  assumption.  On  the 
contrar}',  everything  which  we  actually  know,  as  distinguished 
from  what  we  conjecture  to  be  true,  or  would  like  to  have  true,  for 
the  satisfaction  of  certain  of  our  quasi-scientific  or  ethical  impulses 
favors  this  assumption.  And  no  other  assumption,  substantially 
different  from  this,  is  compatible  with  the  facts  of  experience. 


CHAPTEE  lY. 
THE   MIND  AS  EEAL  BEING. 

§  1.  No  attempt  need  be  made  to  conceal  the  fact  that  the  last 
three  chapters  have  given  to  the  phenomena  aad  laws  of  Physi- 
ological Psychology  a  "  metaphysical "  treatment.  In  the  intro- 
duction (see  §  5)  to  the  scientific  discussion  of  the  subject,  the  in- 
tention finally  to  raise  and  answer  certain  metaphysical  questions  as 
to  the  nature  of  Mind  was  frankly  avowed.  Indeed,  since  all  dis- 
cussion of  those  assumptions  which  underlie  our  experience  of  what 
we  call  "  reality  "  is  metaphysical,  it  is  not  easy  to  see  how  the 
science  of  mind — from  whatever  point  of  view  approached — can  be 
thorough  and  conclusive  without  involving  metaphysics.  In  this, 
the  concluding  chapter,  certain  still  more  distinctively  metaphysi- 
cal inquiries  must  be  briefly  pursued.  The  mind  has  been  spoken 
pf  as  "real,"  "spiritual "  (or  non-material),  a  "unit-being,"  etc. 
These  are  terms  which  require  further  explication.  What  is  meant 
by  speaking  of  the  mind  as  a  real  being?  What  is  it  to  be,  in 
reality,  f^piritual  rather  than  material  ?  W^hat  is  the  real  nature  of 
that  unity  which  belongs  to  mind  ;  and  on  what  grounds  do  we 
affirm  that  the  mind  is  a  "  unit-being  ?" 

Thus  far  the  effort  has  constantly  been  made  to  maintain  a  close 
connection  between  the  answer  given  to  semi-metaphysical  inquiries 
and  the  facts  of  physiological  psychology.  In  rendering  such  an- 
swer the  appeal  has  constantly  been  taken  to  the  facts.  Should 
the  facts,  in  any  case  of  appeal,  not  betir  out — or,  at  least,  should 
they  contradict — the  conclusions  alleged  to  be  based  upon  them, 
then  the  conclusions  must  be  modified,  or  change  the  basis  on 
which  they  assume  to  rest,  or  utterly  fall.  But  in  answering  the 
more  distinctively  metaphysical  questions  now  raised  as  to  the  nat- 
ure of  mind,  the  jDsycho-physical  facts  are  of  little  direct  assist- 
ance. Such  questions  are  fitly  raised  at  the  conclusion  of  psycho- 
physical researches  only  because  these  researches  have  led  us  to  a 
certain  view  as  to  the  nature  of  the  subject  of  the  researches — 
namely,  as  to  the  nature  of  the  mind. 

§  2.  The  mind  is  a  "  real "  being  in  the  highest  sense  in  which 


THE    POPULAR   IMPRESSION.  669 

any  finite  being  can  be  real.  Indeed,  its  claim  to  be  considered 
real  is  more  indisputable  than  the  same  claim  as  put  forth  for  any 
material  thing  ;  it  is  unique.  The  reality  of  mind  underlies  and 
makes  possible  all  our  knowledge  of  other  real  beings,  and  all  our 
assumptions  as  tp  the  existence  of  such  beings.  It  is  only  on  con- 
dition of  granting  its  reality,  in  the  highest  sense  of  the  word,  that 
we  can  affirm  the  reality  of  other  beings. 

There  can  be  no  doubt  that  the  popular  impression  attributes  a 
reality  to  material  things  which  it  does  not  consider  to  be  pos- 
sessed by  the  mind.  This  impression  makes  the  clearly  visible 
and  hard,  tangible  substances,  experience  of  which  constitutes  so 
injj5ortant  a  part  of  ordinary  working-day  life,  the  test  and  stand- 
ard of  the  most  indubitable  reality.  Substantial  as  a  rock  (that 
is,  a  presentation  of  sense  which  consists  of  certain  qualities  made 
known  especially  to  the  tactual  and  muscular  senses)  ;  and  unsub- 
stantial as  a  day-dream  (that  is,  a  series  of  representative  images 
largely  free  from  all  admixture  of  presentations  of  sense) — thus 
does  the  popular  estimate  express  itself  with  respect  to  the  reality 
of  the  phenomena  referable  to  things  as  compared  with  the  pure 
states  of  mind.  Materialistic  objections  to  the  reality  of  mind, 
when  made  to  rest  upon  scientific  data,  repeat  and  confirm  the 
popular  impression.  These  objections  ordinarily  assume  that  no 
doubt  can  be  raised  as  to  the  reality  of  material  "Things."  Such 
things  as  are  real  in  the  highest  sense  of  the  word,  however,  are 
not  now  understood  in  the  same  way  as  the  things  indicated  in  the 
popular  impression.  Only  the  atoms,  or  elemental  and  permanent 
factors  which  enter  into  the  comjDosition  of  all  the  objects  of  sense, 
are  held  from  the  scientific  point  of  view  to  be  real  in  the  highest 
sense  of  the  word. 

The  things  of  experience  by  the  senses  are  admitted  to  be  con- 
stantly changing,  and  at  no  time,  extra-mentally,  to  resemble  the 
unchanging  material  realities  with  which  science  deals.  Things, 
as  they  appear  to  the  eye  and  to  touch,  are  spread-out,  continuous, 
without  empty  space  between  them,  and  for  the  most  part  motion- 
less, except  as  they  are  moved  in  masses  by  application  of  external 
energy.  Things  as  they  really  are,  however,  are  neither  spread- 
out,  nor  continuous,  nor  motionless.  On  the  contrary',  they  consist 
of  a  countless  number  of  invisible  and  intangible  real  beings,  called 
atoms,  that  are  ceaselessly  moving,  with  incredible  velocity  and  in- 
tricateness  of  changing  directions,  in  empty  space,  and  according 
to  forces  inherent  in  them.  These  atoms  are  real,  and  have  always 
been — the  sole  element  of  all  which  appears  as  real ;  so  this  form 
of  quasi-scientific  metaphysics  goes  on  to  declare. 


670  THE   KEALITY    OF   MIl^D. 

On  the  other  hand,  it  is  argued  by  certain  advocates  of  the  fore- 
going  \ie\v  that  the  so-called  mind  is  wanting  in  every  characteristic 
which  could  justly  entitle  it  to  be  called  a  reality.  Certainly  it  is 
not  adapted  to  win  the  popular  respect  as  a  hard  and  sohd  sub- 
stance, which  it  is  difficult  to  move,  and  imjoossible  to  remove  from 
the  sphere  of  possible  sensations.  "What  is  the  mind,  in  reality  ? 
It  cannot  be  seen  or  touched,  or  apprehended  by  any  of  the  senses. 
It  cannot  be  imaged  as  spread  out  in  space,  or  as  space-filling,  by 
virtue  of  some  physical  energy  streaming  uninterruptedly  forth 
from  the  mathematical  point  at  which  it  is  situated.  It  can  do 
nothing  except  through  the  body  ;  that  is  to  say,  all  that  is  done, 
which  could  possibly  be  referred  to  the  mind,  is  really  done  by  the 
body.  And  the  body  is  a  material  mechanism,  which  is  nothing 
except  as  it  is  constructed  out  of  the  same  atoms,  with  their  inherent 
forces,  which  have  composed  the  star,  the  crystal,  the  flower ;  and 
which  can  do  nothing  except  as  the  ceaseless  play  of  the  energies 
of  great  Nature  (of  which  it  is  a  point,  a  part)  are  kept  j)laying 
through  it.  Without  the  physical  mechanism,  as  a  real  existence, 
there  is  no  manifestation  of  so-called  mind,  no  manifestation  actual, 
possible,  or  conceivable.  And  when  this  mechanism  is  dissolved, 
the  mental  phenomena,  so  far  as  appears,  wholly  cease,  W^hat, 
then,  is  Mind  ?     WTiat  claim  to  reality  can  it  jDOSsibly  make  valid  ? 

More  particularly,  certain  jjuzzling  questions  regarding  the  nature 
of  the  mind's  behavior  may  be  raised  by  the  advocates  of  the  same 
foregoing  view.  Where  is  the  real  mind,  it  may  be  asked,  when 
consciousness  is  gone,  as  in  swooning  or  deep  sleejD  ?  W^hat  becomes 
of  the  mental  Being  when  the  mental  faculties  one  by  one  drop 
away,  as  in  cases  of  general  paralysis  ?  WTiat  worthy  kind  of  real- 
ity can  belong  to  the  subject  of  j^henomena  so  evanescent  and  tem- 
porary, so  incapable  of  being  measured,  and  weighed,  and  related 
to  the  permanent  forces  and  beings  of  the  material  world  ?  More- 
over, if  mind  is  a  real  being,  what  shall  be  said  in  answer  to  the 
inquiry,  why  certain  of  the  lower  animals  can  apparently  divide  up 
their  souls  by  fission  of  their  physical  structure  ?  And  cannot  even 
man's  proud  unity  of  real  being  become  disturbed  by  the  accident 
or  disease  which  results  in  a  double  consciousness,  or  in  the  loss 
of  all  previously  acquired  knowledge — of  the  mind  as  previously 
existing  and  developed  ? 

§  3.  That  many  puzzling,  and  even  unanswerable,  questions  can 
be  asked  concerning  the  nature  of  the  mind,  we  have  no  interest  to 
deny.  Doubtless,  if  difficulties  growing  out  of  our  inability  wholly 
to  clear  up  our  ideas  of  "real  being,"  "self-identical  and  perma- 
nent existence,"  etc.,  are  objections  to  believing  that  any  real  beings 


'       THE    POPULAR    IMPRESSION.  671 

exist,  they  are  also  objections  to  our  believing  in  the  reality  of  mind. 
But  certainly  it  is  one  thing  to  ask  unanswerable  questions  regard- 
ing the  ultimate  nature  of  any  particular  real  beings,  so  called,  and 
another  thing  to  prove  that  our  belief  in  the  existence  of  such  real 
beings  is  unfounded.  Moreover,  the  fact  that  we  cannot  conceive 
of  or  define  the  real  being  of  the  soul,  in  terms  which  apply  to 
material  things,  is  cheerfully  conceded.  Indeed,  it  is  this  general 
fact  ujDon  which  chief  reliance  is  placed  to  prove  that  the  being  of 
the  soul  is  unlike  that  of  "Things" — is  non-material,  or  spiritual. 
But  how  can  this  fact  prejudice  the  claim  of  the  soul  to  be  real,  un- 
less it  has  previously  been  established  that  to  be  hard,  and  round, 
etc.,  or  to  be  a  minute  material  bit  (an  atom)  ceaselessly  in  move- 
ment, is  necessary  in  order  really  to  be  at  all  ?  The  truth  is,  how- 
ever, that  both  the  popular  impression  and  the  more  scientific 
theory,  just  so  far  as  they  can  cogently  be  urged  against  the  reality 
of  spiritual  being,  themselves  rest  on  the  most  unverifiable  and  ab- 
surd assumptions. 

The  popular  conviction  of  the  indubitable,  and,  as  it  were,  supe- 
rior reality  of  certain  classes  of  things  is  easily  explained  as  the 
necessary  result  of  the  development  of  experience.  All  things 
which  are  pre-eminently  real,  in  this  meaning  of  the  Avord,  are  cog- 
nizable by  means  of  tactual  and  muscular  sensations  marked  by  a 
strong  color-tone  of  feeling.  Things  merely  smellable  have  no 
"reality,"  in  this  sense  of  the  word,  because  they  are  not  apprecia- 
ble by  touch  and  offer  no  muscular  resistance.  We  cannot  put  our 
hands  on  the  effluvia  which  excite  the  olfactory  nerve  ;  the  air  when 
laden  with  sweet  and  sickening  odors  is  not  tangible  or  impenetra- 
ble. Real  things — that  is,  things  which  can  be  seen  and  handled — 
are,  however,  regarded  as  the  sources  of  our  sensations  of  smell. 
What  is  true  of  sensations  of  smell  is  also  true,  in  less  degree,  of 
sensations  of  sound.  But  in  the  case  of  sound  we  are  generally 
able  at  once  to  refer  the  origin  of  the  acoustic  sensation  to  some 
so-called  real  "Thing."  Objects  tasted  are  popularly  regarded  as 
real,  because  they  are  objects  which  are  handled  before  tasted,  and 
constantly  touched  as  they  are  being  tasted  in  the  mouth.  A  "bad 
taste  in  the  mouth  "  is  not  regarded  as  giving  evidence  of  the  pres- 
ence of  any  real  thing  ;  it  may  simply  be  regarded  as  a  sensation 
located  in  that  region.  Accordingly,  one  does  not  consider  one's 
self  to  be  tasting  one's  own  mouth  as  a  real  thing,  although  one 
may  say  that  the  mouth  has  a  bad  taste. 

Even  when  the  presentation  of  sense  is  a  clearly  visible  object, 
it  does  not  necessarily  seem  to  have  the  characteristics  of  a  real 
thing.     For  the  object  of  vision  readily  and  quickly  changes  its 


672  THE   REALITY   OF   MIND. 

color,  apparent  magnitude,  characteristics  of  superficies,  and  visible 
outlines  as  a  solid.  Moreover,  everybody  knows  that  his  eyes  have 
often  deceived  him  ;  even  when  they  have  been  closed  visual  im- 
ages have  appeared  before  the  mind,  such  as  could  not  possibly 
represent  any  so-called  reality.  But  the  nature  of  tactual  and  mus- 
cular sensations  is  different  from  the  visual  in  several  important 
particulars.  Such  sensations,  on  bestowing  the  requisite  attention, 
may  ordinarily  be  brought  strongly  into  consciousness.  They  do 
not  so  readily  change  their  quality  regarded  as  coming  to  us  from 
an  apprehension  of  the  properties  of  things.  The  feeling  of  effort 
colors  them  highly  ;  and  the  pain  from  being  struck,  pressed, 
pinched,  or  impeded,  is  a  frequent  accompaniment.  Therefore, 
children  are  educated  in  their  knowledge  of,  and  belief  in,  a  world 
of  reality  by  being  constantly  resisted  by  material  things ;  and  adults 
naturally  suppose  that  when  they  can  lay  hands  on  an  object  they 
know  that  it  really  is,  and  what  it  really  is,  with  a  certainty  impos- 
sible in  any  other  way. 

It  wholly  escapes  the  ordinary  observation  that  the  same  assump- 
tions— whether  they  be  deemed  verifiable  or  unveritiable — underlie 
the  conviction  of  the  reality  of  things  tangible  which  belong  to 
the  operation  of  all  the  senses.  It  is  true,  as  experience  shows, 
that  tactual  and  muscular  sensations  are,  from  their  very  nature, 
and  from  the  manner  and  frequency  of  their  recurrence,  pecul- 
iarly adapted  to  serve  the  mind  well  in  those  acts  of  synthesis 
by  which  it  constructs  the  real  things  of  its  experience.  But  this 
fact  does  not  in  the  least  diminish  the  force  of  the  other  fact — 
namely,  a  certain  assumption  or  postulate  as  to  an  exti'a-mental 
reality  (an  X,  which  is  not  any  one  of  the  attributes — a,  b,  c,  etc. — 
of  the  "Thing,"  but  which  is  the  subject  or  ground  of  them  all) 
underlies  and  conditions  all  the  apiDrehensions  of  sense.  Without 
granting  and  using  this  assumption  we  cannot  affirm  that  even  by 
tactual  and  muscular  sensations  we  know  any  reality  whatever, 
beyond  the  real  fact  that  so  our  own  minds  stand  affected  with  the 
presentation  of  an  object  of  sense.  If  the  popular  impression  con- 
cerning the  reality  of  "things  "  does  not  extend  beyond  this  simple 
act  of  self-knowledge,  as  it  were,  it  certainly  forms  no  ground  for 
affirming  the  superior  and  undoubted  nature  of  such  reality. 

§  4.  The  cause  of  the  scientific  objector  to  the  reality  of  mind,  as 
standing  on  an  equality,  with  respect  to  the  cogency  of  its  evidence, 
with  those  material  atoms  about  whose  reality  he  tolerates  no  doubt, 
is  not  a  whit  better  off  than  is  that  of  the  popular  impression.  In- 
deed, it  is  by  no  means  so  good.  That  ready-made  "  things  "  really 
exist  in  independence  of  mind  (meaning  by  such  "things"  the  ob- 


THE   SCIENTIFIC    OBJECTION.  673 

jects  of  everyone's  immediate  experience)  is  a  proposition  which  it 
involves  fewer  doubtful  elements  to  maintain  than  the  proposition 
that  so-called  "  atoms  "  have  such  existence.  It  is  time  to  raise  the 
question  :  How  can  one  know,  so  confidently,  that  those  cerebral 
molecules  exist  extra-mentallj,  with  all  their  incalculable  and  almost 
inconceivable  motions,  on  whose  real  being  the  phenomena  of  mind 
are  sometimes  made  to  depend?  The  brain — it  is  claimed  by  Ma- 
terialism— may  be  made  responsible  for  mental  phenomena,  for  the 
latter  are  mere  manifestations  in  consciousness  of  the  changes  which 
are  going  on  in  the  material  constituents  of  which  this  organ  is 
really  composed ;  there  is  no  need  of  a  real  non-material  being  as 
the  subject  of  the  mental  phenomena ;  the  physical  phenomena, 
however,  must  have  some  real  being  as  their  subjects  ;  such  reality 
is  to  be  found  in  the  molecules  of  the  brain.  But  what  are  the 
grounds  and  the  nature  of  our  knowledge  of  this  wonderful  con- 
jurer styled  the  brain  ? 

The  so-called  scientific  argument  against  the  reality  of  mind,  as 
often  applied,  may  be  stated  in  terms  somewhat  like  the  foregoing. 
Little  examination  is  needed,  however,  to  show  that  its  conclusive- 
ness involves  certain  assumptions  which  cannot  themselves  be  vali- 
dated without  weakening  or  destroying  the  very  ground  on  which 
the  argument  is  itself  based.  Let  the  case  be  tried  by  making  a 
beginning  with  that  sort  of  testimony  with  which  everyone  is  most 
familiar.  I  know  that  I  think,  feel,  will ;  that  is  to  say,  phenomena 
take  place  in  consciousness  which  there  is  no  conceivable  way  of 
describing  except  by  attributing  them  to  the  subject  of  all  con- 
sciousness— to  the  self-conscious  "  me  "  called  mind.  But  because  I 
cannot  perceive  this  subject  of  all  consciousness  as  an  extended  and 
external  somewhat — a  "  Thing  "  so  large,  and  shaped  and  colored 
in  just  such  a  manner,  with  a  definitely  hard  or  soft  feel — that  is  to 
say,  because  I  do  not  appear  to  myself  in  consciousness  to  be  just 
such  a  kind  of  being  as  are  some  of  the  objects  of  my  perception, 
I  begin  to  raise  the  question  whether  this  subject  (the  "I"  that 
thinks,  etc.)  has  any  real  being  at  all.  May  it  not  in  fact  be,  I  ask 
myself,  that  some  "thing,"  or  collection  of  things,  like  those  which 
I  have  often  seen  and  felt,  is  the  subject  to  which  the  thoughts 
and  feelings  and  acts  of  will  that  I  haVe  called  "  mine  "  should  be 
attributed?  Of  course,  if  this  question  is  to  be  answered  in  the 
light  of  modern  physiology  with  even  a  provisional  affirmative,  the 
particular  "thing,"  to  which  such  activities  as  those  I  am  conscious 
of  are  to  be  attributed,  is  my  hrain.  Nothing,  surely,  but  my  brain 
can  think,  and  feel,  and  will — so  to  speak — for  me.  For  if  physical 
science  has  established  anything  whatever  with  regard  to  a  particu- 
43 


C74  THE    EEALITY    OF    MIND. 

lar  organ  or  substratum  of  the  mental  phenomena,  it  is  that  such 
organ  or  substratum  is  the  brain. 

But  the  inquiry  must  next  be  raised :  How  does  one  know  that 
one  has  a  brain,  which  may  serve  as  the  real  substratum  of  the 
phenomena  of  one's  consciousness  ?  It  scarcely  need  be  said  that 
no  one  has  ever  had  any  evidence  presented  directly  to  the  senses 
that  such  organ  exists  within  his  own  cranial  cavity.  To  be  con- 
scious, and  at  the  same  time  to  observe  the  substratum  of  one's 
consciousness,  is  an  unattainable  opportunity.  It  may  even  be 
that  the  ego  (the  "I"  of  consciousness)  which  is  engaged  in  the 
search  for  its  own  real  being  in  a  material  substratum  has  never 
seen  so  much  as  a  single  human  brain.  It  is  certain  that  no  ego 
has  directly  observed  the  molecular  changes  of  any  central  nervous 
mass,  whether  belonging  to  another  or  to  itself,  when  such  mass 
was  engaged  in  the  activities  whose  resultant  the  phenomena  of 
consciousness  are  claimed  to  be.  Since  there  is  such  scarcity  of 
direct  ocular  and  tangible  demonstration  of  a  special  relation  be- 
tween the  brain  and  mental  phenomena,  it  is  plain  that  the  testi- 
mony of  experts  must  be  summoned.  Resort  must  be  had  to  the 
great  anatomists  and  experimental  physiologists  who  have  had  most 
experience  as  to  the  structure  and  functions  of  the  brain-mass. 

It  must,  of  course,  be  confessed  that  no  expert  has  any  more 
direct  evidence  than  every  self-conscious  ego  has  of  the  existence 
of  a  real  material  structure  called  brain,  which  may  account,  by  its 
presence  and  activities,  for  his  own  mental  phenomena.  Nor  can 
he  offer  an}'  evidence  peculiar  to  himself  for  his  belief  that  the  par- 
ticular ego  which  each  one  calls  "  myself"  is  connected  with  a  brain. 
How  many  soever  other  brains  he  may  have  seen,  he  only  knows 
by  a  series  of  very  indirect  and  complicated  inferences  that  any 
individual  whose  brain  lie  has  not  seen  really  possesses  one.  But 
whence  these  inferences  ?  and,  "What  are  the  grounds  on  which  the 
confidence  attached  to  them  is  based?  To  these  questions  only 
one  answer  is  possible.  The  inferences  themselves  are  acts  of 
knowledge,  modes  of  consciousness,  phenomena  of  mind.  The 
only  possible  grounds  of  confidence  in  them,  as  valid  inferences, 
must  be  referred  back  to  our  inherent  faith  in  the  power  of  the 
mind  rightly  to  infer,  from  its  own  phenomena,  the  real  existence 
of  beings  the  phenomena  of  which  it  has  never  perceived.  More- 
over, if  the  mind  had  perceived  the  phenomena  of  its  own  brain, 
there  could  be  nothing  in  the  phenomena  themselves  to  account  for 
the  power  to  make  inferences  which  belong  to  it  as  mind.  On  the 
ground,  then,  of'  an  inferred  reality  called  the  brain,  I  am  asked 
to  dispense  with  my  confidence  in  the  reality  of  the  being  whicli 


THE   ATOMS   AS   AGENTS.  675 

makes  the  inference,  and  which,  at  the  same  time,  makes  a  much 
more  irresistible  inference  as  to  its  own  reality  as  an  active  infer- 
ring force. 

§  5.  The  case  is,  however,  by  no  means  so  favorable,  as  the  state- 
ment just  made  would  imply,  for  that  phase  of  scientific  material- 
ism which  refers  the  phenomena  of  consciousness  to  the  brain  as 
their  sole  cause.  For  it  is  not  in  the  brain,  as  a  mere  mass  of  mat- 
ter whose  structure  and  mechanical  functions  can  be  made  obvious 
to  any  intelligent  observer,  that  the  real  substratum  of  mental  phe- 
nomena must  be  sought.  Considered  as  such  a  mass,  this  organ 
is  no  better  than  any  other  similar  soft  and  pulp-like  bulk.  It  is 
the  wonderful  molecular  constitution,  atomic  play,  and  changing 
dynamic  relations  of  the  invisible  particles  of  this  mass,  which  are 
responsible  for  its  unique  functions.  In  all  the  first  Part  of  our 
investigation  we  saw  how  necessary  physiology  finds  it  to  regard 
the  nervous  centres  as  molecular  mechanisms.  Nothing  that  is  in 
itself  of  first  importance  appears  to  the  eye  of  the  observer  who 
looks  upon  the  freshly  extracted  mass  of  the  human  brain.  And 
when  this  mass  has  been  skilfully  prepared  for  investigation  under 
the  microscope,  the  investigation  itself  does  not  reveal  directly,  to 
the  highest  magnifying  powers  of  the  glass,  the  ultimate  agents 
in  the  wonderful  drama  it  has  been  playing.  These  agents  are  the 
atoms,  to  whose  real  being  and  so-called  "  inherent "  forces  all  that 
is  done  by  the  complicated  mechanism  must  be  referi'ed.  But  the 
existence  of  the  atoms  as  real  beings,  capable  of  acting  on  each 
other  and  of  being  acted  on — how  shall  this  remote  and  obscure 
fact  be  ascertained  ?  And  how  shall  we  learn  what  is  the  nature  of 
these  beings,  so  as  to  determine  whether  or  not  they  are  capable 
of  performing  the  stupendous  task  of  bringing  forth  the  various 
mental  phenomena? 

In  attempting  to  answer  the  last  two  questions  we  are  in  great 
danger  of  losing  completely  all  that  we  have  taken  most  pains  to 
gain.  It  is  to  the  all-powerful  "  atoms,"  with  their  potent  forces, 
that  -we  are  now  looking  as  the  real  subjects  at  once  of  the  molec- 
ular changes  in  the  brain-mass  and  of  the  phenomena  of  conscious- 
ness. From  these  real  beings  and  their  relations  there  must  be 
derived,  not  only  the  activities  which  all  ascribe  to  nervous  matter, 
but  also  those  which  some  are  constrained  to  ascribe  to  conscious 
mind.  And  yet,  how  do  we  know  that  any  real  beings  whatever 
called  atoms  exist  ?  Certainly  not  by  direct  evidence  of  any  of  the 
senses.  Not  even  the  most  pronounced  materialist  would  venture 
to  affirm  that  he  has  seen  or  touched  an  atom,  or  can  demonstrate 
its  existence  and  nature  to  ordinary  observation  through  the  human 


G7G  THE    KEALITY    OF   MIND.  * 

senses.  Atoms  are  supersensible  beings.  Moreover,  tliey  are  hj]pO' 
thetical  existences,  or  beings  whose  existence  is  inferred  in  an  ex- 
tremely roundabout  way  in  order  tbat  we  may  be  able  to  give  to 
ourselves  a  rational  account  of  the  grounds  on  which  certain  classes 
of  phenomena  rest. 

The  phenomena  whose  rational  explanation  seems  most  peremp- 
torily to  demand  some  hypothesis  of  atoms  are  the  phenomena  of 
chemistry.  When,  however,  the  further  inquiry  is  raised  as  to  the 
real  nature  of  the  atoms,  it  is  found  that  modern  physical  science 
is  by  no  means  satisfied  with  its  own  answer.  Dynamical  theories, 
tending  to  resolve  the  atoms  into  mathematical  points  acting  as 
mere  centres  of  force,  contend  with  other  more  realistic  theories 
which  regard  the  atoms  as  simply  the  smallest  bits  of  matter  into 
which  we  can  by  any  known  means  break  ujd  the  larger  collections. 
What  is  meant  by  the  forces  being  "  inherent  "  in  the  atoms  is  a 
still  more  difficult  question  to  answer.  Indeed,  to  this  question  no 
answer  can  be  given  which  gets  much  beyond  the  simjole  declara- 
tion of  the  facts  of  experience  ;  that  is  to  say,  these  hj'pothetical 
and  yet  sole  real  material  beings  are  always  supposed  to  behave, 
with  respect  to  their  motions,  in  the  same  way  under  the  same  re- 
lations, and  something  can  be  done  by  science  toward  measuring 
their  various  motions  in  terms  one  of  the  other. 

Moreover,  the  best  efforts  of  modern  investigation  to  describe 
the  nature  of  the  atoms  appear,  not  only  incomplete,  but  also,  in 
certain  particulars,  self-contradictory.  It  is  certain  that  the  atom 
cannot  be  regarded  as  an  independent  reality.  What  it  is  can  only 
be  described  by  telling  what  it  does  ;  but  in  telling  what  it  does 
we  always  find  ourselves  implj'ing  certain  relations  to  o/Ae/'  atoms. 
That  is  to  say,  we  know  nothing  about  the  nature  of  any  of  the 
atoms  which  does  not  involve  also  comjDlicated  hypotheses  concern- 
ing its  mode  of  behavior  as  caused  by  the  presence  and  mode  of 
behavior  of  other  hypothetical  beings.  In  this  way  the  realitj^  of 
the  atoms  is  made  ultimately  to  depend  on  the  reality  of  some  form 
of  being  that  binds  them  together,  as  it  were,  and  makes  them 
work  to  a  unity  of  plan.  But  here,  again,  we  are  reminded  that  we 
can  form  no  conception  of  a  "plan  "  which  is  not  a  phenomenon  of 
mind,  and  no  conception  of  a  "unity  "  that  does  not  depend  ujDon 
the  unifying  actus  of  the  mind.  Moreover,  all  ideas  of  "relation" 
are  dependent  upon  mental  activities  that  are  quite  without  phys- 
ical analogy.  All  "Things"  are  made  into  the  units  which  they 
appear  to  be  by  the  unifying  action  of  the  mind.  Such  action  is 
implied  in  perceiving  the  things  ;  for  the  study  of  perception,  from 
the  physiological  point  of  view  even,  has  enabled  us  to  show  that 


ATOMS   AS   DUE  TO   MIND.  677 

no  so-called  "  thing "  is  a  ready-made  material  product,  appre- 
hended by  mind  in  a  form  which  is  a  copy  of  some  extra-mental 
being.  In  trying,  therefore,  to  comprehend  what  is  the  nature  of 
those  real  beings  (the  atoms),  on  whose  existence,  activity,  and  rela- 
tions all  mental  phenomena  are  assumed  by  Materialism  to  depend, 
we  find  that  the  picture  we  frame  of  them  is  the  work  of  the  mind. 

§  6.  Accordingly,  the  whole  course  of  argument  and  the  whole 
weight  of  conviction  appear  to  be  the  reverse  of  what  is  assumed 
by  the  objector  to  the  reality  of  mind.  The  material  molecules  of 
the  brain  are  not  beings  about  the  reality  and  exact  nature  of  which 
we  have  the  most  indubitable  evidence — evidence  so  indubitable 
that  we  may  venture  to  press  it  into  the  contradiction  of  the  more 
immediate  data  of  consciousness.  If  these  elements  of  all  physical 
being  are  real,  they  come  to  us  as  inferences  and  hj^potheses  ;  they 
involve  a  vast  amount  of  conjecture,  indirect  inference,  and  unsolved 
difficulties,  or  even  contradictions.  And  if  we  ask,  On  what  au- 
thority are  these  inferences  made  ?  Whence  comes  the  demand  for 
any  rational  explanation  whatever?  Where  do  the  conjecture,  hy- 
pothesis, and  sense  of  difficulty  and  seeming  contradiction  exist? 
then  the  only  answer  to  be  given  to  all  these  questions  refers  them 
to  the  Mind.  What  atoms  and  forces  and  laws  can  be,  or  mean, 
without  the  being  and  activity  of  self-conscious  mind,  is  even  harder 
to  conjecture  than  what  a  color  can  be  which  is  not  seen,  a  sound 
which  is  not  heard,  an  odor  that  is  not  smelled. 

And  now  let  the  attempt  of  materialistic  theory  be  made  anew  ; 
let  it  be  assumed  that  the  phenomena  of  consciousness  have  no 
I'eal  subject  in  the  mind.  Such  phenomena  must,  accordingly,  be 
attributed  to  the  peculiarly  constituted  and  mutually  interacting 
molecules  of  the  brain.  But  these  supreme  physical  beings  are 
themselves,  as  far  as  they  are  the  object  of  knowledge,  pre-emi- 
nently mental  creations  ;  and  the  sole  warrant  for  carrying  them 
over  into  the  realm  of  extra-mental  reality  consists  in  certain  irre- 
sistible convictions  or  assumptions  of  mind.  To  make  their  real 
being  the  account  of  the  mental  phenomena,  and  thus  to  deny  the 
real  being  of  the  subject  of  mental  phenomena,  is  not  only  to  ex- 
plain what  is  most  direct  and  certain  by  what  is  most  indirect  and 
uncertain  ;  it  even  involves  the  wonderful  paradox,  that  the  one  be- 
ing inwhose  active  energizing  all  conceptions  of  all  real  being  arise, 
feels  justified  in  denying  its  own  reality  in  the  supposed  favor  of  cer- 
tain of  its  most  remote  and  donbtfid  conceptions. 

§  7.  What  is  meant  by  affirming  the  reality  of  mind  may  be 
made  obvious  by  pursuing  the  following  train  of  reflections  :  In 
the  development  of  the  mental  life  its  phenomena  come  inevitably 


678  THE   EEALITY   OF   MIND. 

to  divide  themselves  into  two  great  classes.  As  it  appears  to  adult 
experience,  not  only  tlie  unfolding,  but  even  the  very  existence  of 
self-consciousness  seems  to  involve  the  distinction  between  the  ego 
and  the  non-ego — between  the  "I"  with  its  states,  and  the  "Things" 
which  it  knows  with  their  manifold  jDroperties  or  attributes.  Each 
of  these  two  classes  of  phenomena — the  so-called  subjective  and  the 
so-called  objective — is  inevitably  attributed  in  consciousness  to  a 
different  subject ;  the  one  to  the  "  I "  as  its  own  states,  the  other  to 
somewhat  left  undefined,  except  that  it  is  not  the  "  I,"  and  is  called 
"matter,"  "material  substance,"  etc.  (the  unknown  X  which  is  not 
I).  It  is  only  as  involving  all  this  mental  jorocess  that  any  real 
being  is  known  or  believed  to  exist ;  but  the  mind  in  the  develop- 
ment of  experience  inevitably  completes  the  process,  which  involves 
the  assumption  that  real  beings  do  exist,  and  that  all  these  real 
beings  are  either  "  things,"  such  as  I  know,  or  myself  and  other 
conscious  beings,  such  as  I  am.  What  any  real  being  is  can  only 
be  told  by  an  enumeration  of  its  so-called  attributes  ;  and  this  is  as 
true  of  myself  as  of  the  things  which  I  know.  It  is  also  as  true  of 
them  as  it  is  of  myself.  If  the  foregoing  statements  covered  the 
entire  case,  it  would  simply  be  true  that  I  have  no  better  reason 
for  attributing  a  real  Being  to  any  material  thing  than  to  the 
subject  of  consciousness.  But  we  have  already  seen  that  the  pro- 
cess by  which  we  reach  the  real  being  of  the  molecules  of  the 
brain  is  much  more  indirect  and  doubtful  than  that  by  which  we 
reach  the  affirmation  of  a  real  being  for  the  things  of  daily  experi- 
ence and  for  the  subject  of  all  that  experience. 

§  8.  Peculiar  and  cogent  reasons  may  be  given,  however,  which 
further  enforce  and  verify  the  assumption  of  a  real  existence  for 
the  Mind.  We  have  seen  (comp.  Part  IT.,  chap.  X.,  and  the  pre- 
ceding chaps,  of  Part  III.)  that  there  is  a  class  of  so-called  mental 
faculties,  most  important  and  distinctive,  for  the  distinguishing- 
characteristic  of  which  no  physical  analogies  or  correspondences 
whatever  can  be  discovered  or  imagined.  This  is  true  of  memory 
as  active  reminiscence,  of  the  unity  of  consciousness,  of  voluntary 
attention,  and  of  the  relating  activity.  The  existence  of  these 
modes  of  mental  behavior  requires  the  assumption  of  a  charac- 
teristic real  being,  other  than  the  molecules  of  the  brain,  to  which 
they  may  be  referred.  Some  of  these  modes  of  behavior  are  con- 
spicuously unintelligible  and  meaningless  without  granting  such 
an  assumption.  For  example,  an  act  of  recollection  involves  the 
presence  in  consciousness  of  a  state  the  very  essence  of  which  is 
that  it  claims  to  represent  (or  stand  for)  an  absent  past  state  of 
consciousness.      No  way  of  verifying  this  claim  which  does   not 


TO   EE   AND   BE   CONSCIOUS.  679 

involve  its  acceptance  can  possibly  be  devised.  But  tlie  present 
state  of  memory  is  a  state  of  my  consciousness,  and  the  state  which 
it  claims  to  represent  was  also  a  state  of  my  consciousness.  To 
recollect  the  past  state  of  another  consciousness  than  my  own  in- 
volves an  absurdity  ;  to  recollect  a  past  state  otherwise  than  as 
represented  in  a  present  state  of  my  own  consciousness  also  involves 
an  absurdity.  Of  course,  such  reflection  upon  the  nature  of  the 
act  of  memory  affords  no  demonstration  of  the  claim  that  the  sub- 
ject of  the  present  state  is  one  and  the  same  real  being  with  the 
subject  of  the  past  state.  On  the  contrary,  all  demonstration  itself 
rests  on  this  assumption  ;  for  without  accepting  it  as  valid  we  could 
not  reach  the  conclusion  of  any  demonstration.  The  premises  of 
every  syllogism  are  connected  with  one  another  and  with  their 
conclusion  in  a  living  unity  of  thought,  only  on  the  assumption 
that  one  real  being  is  the  subject  of  each  of  the  thoughts  Avhich 
constitute  the  syllogism. 

To  "he  really,"  and  to  be  the  one  permanent  subject  of  changing 
states,  are,  in  our  conception,  but  different  ways  of  expressing  the 
same  truth.  That  really  is  which  is  such  a  subject  of  its  own 
states.  It  is  for  this  reason  that  modern  physical  science  regards' 
the  atoms  as  having  a  permanent  reality  which  does  not  belong 
to  the  composite  structures — the  things  of  our  experience — into 
which  the  atoms  enter.  Every  "  Thing  "  may  perish — that  is  to 
say,  as  such  thing,  it  may  cease  to  be  the  object  of  observation, 
the  subject  of  states.  But  the  atoms  are  supposed  to  remain  with 
unchanged  natures  through  all  the  changes  of  relation  which  they 
may  undergo  toward  other  beings  with  somewhat  similar  natiires. 
Even  if  we  were  obliged  to  adopt  the  hypothesis  of  a  constant 
change  of  states  in  the  interior  of  the  atoms,  since  every  atom 
shows  a  variety  of  possible  activities  according  to  the  relations  in 
which  it  stands  for  the  time  to  other  atoms,  it  is  not  considered 
to  have  lost  its  real  being  or  distinctive  nature  by  changing  its 
states.  For  it — the  atom — can  be  brought  into  the  same  relations 
again,  and  then  it  will  again  display  the  same  modes  of  behavior. 
Its  reality  does  not  depend  upon  its  interior  rigidity,  the  unchang- 
ing nature  of  its  being  ;  it  rather  depends  upon  its  capacity  for 
being  the  subject  of  so-called  states,  and  for  following  a  law  or  an 
idea  which  recalls  it,  as  it  were,  to  the  same  states  when  the  same 
circumstances  recur. 

How  can  it  be  denied  that  all  our  conceptions  of  the  atoms  as 
enduring  subjects  of  various  states  are  derived  from  our  experience 
with  ourselves?  The  "  I  "  which  is  the  subject  of  all  consciousness 
is  accustomed  to  attribute  to  itself  every  state  of  that  great  variety 


680  THE   REALITY    OF  MIND. 

into  which  consciousness  may  be  shaped.  The  states  are  changing, 
they  have  a  transitory  and  phenomenal  being.  But  they  are  all 
states  attributable  to  one  subject.  On  what  ground,  then,  shall  one 
undertake  to  deny  the  confidence  which  the  soul  comes  to  have  in 
itself  as  the  real  and  permanent  subject  of  its  own  states  ?  For  we 
can  form  no  conception  of  real  being  at  all  which  is  not  modelled 
after  this  pattern.  To  have  a  variety  of  changing  states  attributed 
to  it  as  the  subject  of  them  all — this  is  to  demonstrate  in  conscious- 
ness a  claim  to  real  Being.  Unchanging  rigidity,  the  permanence 
of  the  mathematical  point  or  of  the  material  atom,  on  the  supposi- 
tion that  the  latter  undergoes  no  interior  changes  whatever,  if  such 
rigidity  and  permanence  any  where  exist,  constitutes  no  claim  to  the 
title  of  real  being. 

The  soul  exists  in  reality,  above  all  other  kinds  of  being,  because 
it  alone,  so  far  as  we  know  on  good  evidence,  knows  itself  as  the 
subject  of  its  own  states  ;  or,  indeed,  knows  the  states  of  which  it 
is  the  subject  as  states  belonging  to  itself.  But  its  law  is  that  of 
development;  and,  unlike  all  "  things  "  which  are  subjects  of  va- 
rious kinds  of  evolution,  so  called,  the  soul  can  recognize  the  law 
of  its  own  being.  When,  therefore,  we  are  asked  what  the  Mind 
really  is,  we  can  respond  by  telling  what  it  comes  to  be  as  the  re- 
sult of  its  unfolding  under  the  fixed  conditions  of  its  native  powers. 
But  these  "  powers  "  cannot  be  called  native,  as  though  they  were 
actual  achievements  of  the  mind's  inborn  faculties,  or  separate  forms 
of  energy  inherent  in  it,  after  the  analogy  of  the  forces  said  (some- 
what unintelligibly,  it  must  be  admitted)  to  be  "  inherent "  in  the 
atom. 

But  we  do  not  define  the  nature  of  any  real  being  simply  by 
stating  how  it  appears  and  behaves  in  its  most  germinal  and  unde- 
veloped form.  The  tree  explains  the  seed  ;  the  adult  bird,  the 
egg  ;  the  character  of  the  highly  differentiated  product  must  be 
studied  in  order  to  know  the  full  description  of  the  energies  that 
are  potential  in  the  simpler  stages.  It  is  an  undoubted  fact  that 
the  mind  has  a  historj'  in  each  individual  case  ;  and  in  each  case 
such  history  is  a  development.  The  great  service  which  Physiolog- 
ical Psychology  has  rendered  to  the  general  science  of  mind  con- 
sists in  its  description  of  the  nature  and  stages  of  this  develoi^ment, 
so  far  as  concerns  the  jDhenomena  of  sensation  and  perception  by 
the  senses.  This  self-recognizing  unity  of  development  which  be- 
longs to  the  mind  is  a  striking  proof  of  the  validity  of  its  claim  to 
be  considered  a  real  being.  As  the  being  which  acts  and  kuovvs 
itself  as  acting,  which  is  acted  upon  and  knows  itself  as  affected, 
which  is  the  subject  of  states  and  itself  attributes  these  states  to 


•       KOA' -MATERIALITY   OF    MIND.  681 

itself,  which  develops  according  to  a  plan  and  so  remembers  and 
comprehends  the  significance  of  its  past  states  that  it  can  recognize 
the  fact  of  its  own  development — as  such  a  being  the  Mind  is  more 
entitled  to  consider  itself  "  real  "  than  to  consider  real  any  of  the 
various  objects  that,  immediately  or  indirectly,  appear  before  it  in 
the  course  of  its  history. 

§  9.  The  question  whether  the  mind  is  to  be  spoken  of  as  non- 
material  or  "  spiritual  "  scarcely  merits  the  gi-ave  and  lengthy  dis- 
cussion to  which  it  has  often  been  carried.  Materiality,  as  predi- 
cated of  any  real  being,  is  only  a  complex  term  including  a  num- 
ber of  so-called  attributes,  which  are  all  the  subjects  of  experience 
only  as  belonging  to  individual  things.  All  real  things  are  to  be 
called  material  which  have  these  attributes,  so  called.  Primarily,  as 
has  been  frequently  shown  already,  the  attributes  are  simply  modes 
of  the  affection  of  the  mind  which  we  have  learned  to  localize  and 
objectify  as  belonging  to  extra-niental  reality.  But  if  we  raise  the 
question  whether  the  Mind,  too,  is  known  to  itself  as  having  those 
attributes  which  make  up  our  complex,  general  notion  of  "materi- 
ality," no  one  would  find  it  easy  to  think  of  giving  this  question  an 
affirmative  answer.  The  mind  attributes  to  "things"  the  qualities 
of  extension,  impenetrability,  and  all  the  various  subordinate  mod- 
ifications of  these  qualities.  It  perceives  these  things  as  colored, 
cold,  hot,  rough,  smooth,  etc.  But  it  does  not  attribute  such  quali- 
ties to  itself  ;  it  can  find  nothing  in  the  modes  in  which  it  mani- 
fests itself  to  itself  which  would  warrant  the  application  of  similar 
terms  to  these  modes  of  its  own  behavior. 

Indeed,  all  the  terms  which  do  apply  to  the  recognized  qualities 
of  mind  have  to  be  understood  as  figurative  when,  having  been 
borrowed  from  physical  relations,  they  are  made  to  apj)ly  to  psychi- 
cal states.  Even  in  those  cases  where  the  analogy  seems  almost 
to  amount  to  an  identity,  closer  inspection  shows  that  this  seem- 
ing does  not  correspond  to  the  actual  fact.  For  example,  we  do 
attribute  quantity  to  sensations  and  feeling.  But  when  the  suffer- 
ing from  pressure  becomes  more  intense,  we  do  not  regard  the 
mind  as  actually  passing,  like  some  material  thing,  under  a  heav- 
ier load  (sub-fero),  against  which  it  must  either  bear  up  or  break, 
through  the  physical  strain.  Just  so,  movements  of  the  mind  are 
not  to  be  defined  as  changes  of  its  position  with  relation  to  other 
things  in  space.  We  are,  then,  surely  warranted  in  affirming  that, 
so  far  as  the  mind  has  any  immediate  information  as  to  what  quali- 
ties should  be  assigned  to  itself  and  what  to  "  things  " — which  it 
always  looks  upon  as  not-itself — it  is  compelled  to  regard  itself  as 
>*on-material. 


6S2  SPIRITUALITY   OF   MIND. 

"We  have  no  way,  however,  of  telling  what  is  the  nature  of  any 
so-called  real  being  except  by  enumerating  its  qualities,  or  those 
modes  of  behavior  which  we  attribute  to  it  on  account  of  its  affect- 
ing our  consciousness  in  certain  definite  ways.  To  attempt  to  re- 
gard the  mind  as  material,  when  it  manifests  itself  to  itself  as 
non-material,  compels  us  either  to  use  the  word  "  material "  in  an 
unwonted  and  unauthorized  way,  or  else  to  attribute  to  matter  in 
general  certain  occult  powers  which  it  never  manifests  itself  to  the 
mind  as  possessing,  and  which  make  it  really  to  be  quite  different 
from  what  its  manifestation  of  itself  would  indicate. 

The  only  way  of  maintaining  the  materiality  of  mind  would  then 
appear  to  be  that  of  denying  its  real  existence  at  all,  and  of  attrib- 
uting its  phenomena  to  the  material  molecules  of  the  brain  as  their 
real  and  material  substratum  or  basis.  But  the  untenable  nature 
of  this  view  has  already  been  sufficiently  indicated.  Or  perhaps  a 
strong  temptation  may  be  again  felt,  at  this  point,  to  recur  to  the 
hypothesis  of  a  third  somewhat,  a  "  two-faced  unity,"  which  is  the 
ground  of  the  phenomena  of  both  body  and  mind.  But  such  hypoth- 
esis can  throw  no  light  whatever  on  the  inquiry  whether  the  mind 
is  material  or  non-material.  The  phenomena  we  call  "  mental," 
and  attribute  to  the  subject  of  consciousness,  would  remain  just  as 
radically  uulike  those  which  we  call  "  physical,"  and  attribute  to 
matter,  after  making  the  hypothesis  as  before.  And  to  the  hypoth- 
esis itself  the  same  objections  would  lemain  opposed. 

The  negative  conclusion  that  mind  is  won-material  is  quite  in- 
evitable for  everyone  who  admits  that  mind  is  a  real  being  with 
any  nature  whatever. 

§  10.  It  is  not  difl&cult,  also,  to  show  that  we  must  make  the  cor- 
x'esponding  positive  statement,  and  affirm  the  spirituality  of  mind. 
This  we  can  do  with  confidence,  however,  only  so  long  as  we  mean 
by  the  term  "spirituality  "  simply  to  sum  up  and  express  in  one  word 
the  list  of  attributes  which  describes  the  kiK)wn  activities  of  mind. 
To  perceive,  feel,  think,  will — in  brief,  to  be  conscious  in  some  one 
of  the  various  forms  of  conscious  life — this  is  to  be  positively  spirit- 
ual, in  the  only  sense  in  which  we  are  entitled  to  affirm  spirituality 
of  mind  as  such.  As  soon  as  we  conceive  of  spirituality  as  some 
ethereal  extension  of  thinking  substance,  we  enter  upon  the  vain 
effort  to  conceive  of  mind  under  terms  of  matter,  and  at  the  same 
time  escape  the  consequences  of  so  conceiving  of  it.  Nor  can  we 
hope  to  vindicate  for  the  mind  such  spirituality  as  would  be  implied 
in  its  being  freed  from  all  relations  to  material  things,  or  from  de- 
pendence for  the  modes  of  its  being  upon  the  material  substratum 
of  the  brain.     How  spirit,  in  the  sense  of  disembodied  or  unem- 


•MENTAL    ACTIVITIES   SPIRITUAL.  683 

bodied  mind,  would  perceive,  and  feel,  and  think,  and  will,  is  a  ques- 
tion toward  the  answer  to  which  we  can  make  no  beginning.  To 
attempt  its  answer  at  all  involves  us  in  the  vain  effort  to  use  the 
very  relations  which  are  most  inseparately  connected  with  the  con- 
scious activity  of  the  mind  in  such  way  as  to  escape  from  the  con- 
trol of  the  relations  themselves. 

It  is  true,  nevertheless,  that  a  marked  difference  exists  in  the 
directness  and  intimacy  which  belong  to  different  classes  of  mental 
states,  as  regards  their  comparability  to  the  classes  of  physical 
stimuli  which  rouse  the  mind  to  its  fundamental  activities.  Those 
which  appear  to  be  most  indirectly,  and,  as  it  were,  loosely  related 
to  these  fundamental  activities  are  fitly  most  relied  upon  to  show 
the  spiritual  nature  of  mind.  To  control  the  mental  train  as  dis- 
tinguished from  being  a  passive  member  of  a  mental  mechanism, 
to  reason  so  as  to  deduce  conclusions  and  make  inductions  to  gen- 
eral laws,  to  recognize  the  call  of  duty,  and  to  call  up  and  classify 
in  the  consciousness  the  lofty  and  complex  ideas  which  answer  to 
words  like  "  beauty,"  "  truth,"  and  "  God  " — these  and  other  simi- 
lar operations  of  the  mind  pre-eminently  emphasize  its  spirituality. 

§  11.  In  somewhat  the  same  way  must  it  be  admitted  that  the 
question  of  the  unity  of  mind  has  given  rise  to  much  fruitless  and 
by  no  means  altogether  pertinent  debate.  The  attempt  to  conceive 
of  the  mind  as  a  unit-being,  constituted  after  the  analogy  of  those 
physical  structures  which  we  are  accustomed  to  regard  as  unities, 
inevitably  leads  to  confusion  and  error.  The  important  psycho- 
logical fact  is,  that  there  is  no  one  of  these  physical  unities  which 
does  not  derive  its  unity  from  the  unifying  actus  of  the  mind.  This 
statement  is  true  of  each  such  so-called  unity,  whether  it  is  per- 
ceived as  one  or  is  conceived  of  as  one.  The  unity  which  belongs 
to  the  percept  finds  its  source  in  the  synthetic  activity  of  the  per- 
ceiving mind ;  the  unity  of  the  conception,  in  the  unifying  activity 
of  the  mind's  relating  faculty.  It  is  sometimes  supposed,  however, 
that  an  atom  which  should  have  no  parts,  be  perfectly  homogeneous 
throughout,  and  so  incapable  of  changes  of  its  interior  states,  would 
be  the  highest  possible  type  of  a  unity  of  real  being.  Nothing- 
could  ever  happen  to  disturb  or  destroy  such  a  unity.  Wherever 
in  all  space  it  might  be  moved,  or  whatever  in  all  time  might  hap- 
pen to  it,  it  could  ex  hijpothesi  never  be  made  two.  If,  now,  such  a 
unit-atom  were  to  be  endowed  with  consciousness  and  spiritual  be- 
ing, how  secure  would  its  unity  continue  to  be  !  Unlike  the  mind 
of  man,  it  could  not  fear  that  some  rude  concurrence  of  other 
atoms,  not  of  the  right  affinities,  or  setting  themselves  in  untoward 
relations,  would  dissolve  its  complex  material  substratum  and  so 


684  THE   UNITY   OF   MIND. 

destroy  its  spiritual  oneness.  The  molecules  of  tlie  human  brain 
ai'e  in  number  beyond  computation ;  they  are  highly  complex  and 
unstable  compounds  ;  they  are  not  so  protected  by  their  inclosure 
in  the  cranial  cavity  as  to  make  them  invulnerable  against  all  man- 
ner of  assaults.  In  how  dangerous  a  position,  then,  is  this  so  highly 
valued  unity  of  our  present  spiritual  organization  ! 

Now,  it  must  be  admitted  that  such  a  thinking  atom  would  be  in 
far  less  danger  of  suffering  from  the  death  of  the  physical  basis  of 
its  tliought  than  is  the  thinking  man.  But  two  considerations  of 
great  importance  are  likely  to  be  overlooked  in  the  mere  making 
of  the  hypothesis  of  such  an  atom.  Surely  such  an  atom  could  hard- 
ly have  any  experience  corresponding  to  what  we  call  the  unity  of 
our  consciousness  ;  and  if  it  had  any  unity  of  consciousness  what- 
ever, such  unity  could  no  more  be  explained  as  arising  out  of,  or 
conditioned  upon,  the  simplicity  of  the  physical  being  of  the  atom 
than  the  unity  of  our  consciousness  can  be  explained  as  arising  out 
of,  or  conditioned  upon,  the  complexity  of  our  physical  being. 

It  is  impossible  to  see  how  a  unity  of  consciousness  at  all  resem- 
bling what  we  understand  by  the  term  could  find  an  adequate  ma- 
terial substratum  in  a  single  rigid  atom.  In  other  words,  if  a  spirit- 
ual being  having  a  unity  of  consciousness  were  brought  into  si^ecial 
psycho-physical  relations  with  a  material  being  incapable  of  any 
interior  changes,  because  possessed  of  no  parts  to  undergo  change, 
these  relations  would  have  to  be  totally  different  from  any  which 
we  can  conceive  of  as  holding  between  the  body  and  mind  of  man. 
For  the  very  nature  of  the  mind's  unity  is  dependent  upon  that 
variety  of  exj^eriences  which  is  occasioned  in  the  miud  through  the 
changing  states  of  the  brain.  The  physical  basis  of  the  human 
mind  is  undoubtedly  an  extremely  complex  system  of  interacting 
molecules.  Certain  relations  can  be  traced  between  the  character 
of  these  physical  interactions  and  the  character  of  the  states  arising 
in  the  mind.  These  states  depend  for  their  character,  and  even  for 
their  very  existence,  upon  the  occurrence  of  the  corresponding 
material  changes.  A  brain  that  is  not  in  a  ceaseless  change  of  ac- 
tivities of  the  peculiar  sort  called  "  neural  "  is  a  dead  brain,  so  far 
as  its  influence  on  the  mind  is  concerned  ;  such  a  brain  could  not 
serve  as  the  substratum  or  physical  cause  of  mental  phenomena. 
Comparative  anatomy  shows  us  that  the  greater  the  number  of 
molecules,  and  the  larger  the  variety  and  the  size  of  the  organs 
specially  related  to  the  mental  processes,  the  richer  in  variety  and 
nobler  in  quality  the  mental  processes  themselves  become.  More- 
over, so  far  as  we  can  ascertain,  the  highest  unity  of  consciousness 
belongs  in  connection  with  the  greatest  complexity  of  the  material 


THE    UNITY    OF   THE   ATOM.  685 

substratum.  The  animals  whicli  have  the  largest  cerebral  develop- 
ment appear  to  have,  too,  not  only  the  most  manifold  and  extensive 
mental  life,  but  also,  in  the  highest  degree,  the  capacity  for  attrib- 
uting the  phenomena  of  that  life  to  one  subject.  Those  psychical 
activities  which  are  connected  with  the  physical  interaction  of  the 
greatest  number  of  material  elements  are  the  most  numerous  and 
significant ;  and  they  are,  also,  actually  most  perfectly  harmonized 
into  a  higher  unity  of  spiritual  self-conscious  being. 

§  12.  No  information  derived  from  the  study  of  Physiological 
Psychology  warrants  us  in  affirming  that  a  highly  developed  self- 
conscious  existence  must,  from  the  universal  necessities  of  the  case, 
be  united  with  a  vastly  complex  material  structure  like  the  human 
brain.  Such  study  does,  however,  compel  us  to  affii'm  that  such 
a  unity  in  variety  as  is  the  human  mind  cannot  be  conceived  of 
in  dependence  upon  the  movements  in  space  of  a  single  jjerfectly 
rigid  and  unchanging  atom.  The  development  of  human  experi- 
ence is  conditioned  upon  the  arising  in  consciousness  of  many 
sensations  of  varied  quantities,  qualities,  and  orders  in  time  ;  upon 
the  synthesis  of  these  sensations  into  presentations  of  sense  ;  and 
upon  the  recall  of  the  presentations  in  the  form  of  I'epresenta- 
tive  ideas.  What  experience  would  be,  if  its  basis  were  not  laid 
in  such  rise  and  combination  and  i-ecurrence  of  sensations,  we  can- 
not even  conjecture.  In  the  highest  flights  of  imagination,  i:i  the 
profoundest  explorations  of  reflection,  we  never  escape  out  of  the 
influences  arising  from  this  basis.  The  nature  of  this  psychical 
basis  of  sensation  and  perception  depends  upon  the  nature  of  the 
physical  basis  of  the  living  and  acting  brain.  In  other  words,  what 
sensations  and  perceptions  constitute,  at  least  in  part,  the  "  stuff" 
of  all  consciousness  depends  upon  what  the  molecules  of  the  cen- 
tral nervous  system  are  doing.  We  cannot  even  conceive  of  any 
other  relations  as  possible  between  the  mind,  on  the  one  hand, 
and  the  brain,  on  the  other,  than  relations  between  a  system  of 
moving  molecules  and  a  corresponding  change  of  conscious  states. 

§  13.  Furthermore,  the  unity  of  a  single  indestructible  and  eter- 
nally unchanging  atom  would  afford  no  explanation  of  a  mental 
unity.  In  the  case  of  man's  mind  and  brain,  the  vai'iety  of  the 
nervous  changes  in  part  explains  the  variety  of  the  mental  states  ; 
but  nothing  in  the  changing  relations  of  the  innumerable  moving 
molecules  throws  any  clear  light  on  the  origin  of  the  unity  of  mind 
in  consciousness.  A  material  being  absolutely  without  distinction 
of  parts  would  be,  for  that  fact,  no  better  fitted  to  become  conscious 
of  itself  as  one.  A  series  of  states  of  consciousness  can  indeed  be 
attributed  by  our  imagination  to  such  a  being.     From  the  purely 


686  THE   UNITY    OF   MIISTD. 

psychological  point  of  view  we  can  conceive  of  the  unit-atom  as 
having  an  experience  resembling  our  own.  We,  in  our  conscious- 
ness, can  imagine  such  a  being  as  the  subject  of  states,  and  as 
attributing  each  of  these  states  to  one  and  the  same  subject — 
namely,  the  "  I "  of  the  unit-atom — after  the  fashion  of  our  cus- 
tomary mental  behavior.  But  this  is  quite  a  different  thing  from,  ex- 
j)laining  the  consciousness  of  such  an  atom  as  arising,  with  respect 
to  its  unity,  out  of  the  material  nature  of  the  atom.  By  the  very 
hypothesis,  the  material  nature  of  this  particular  kind  of  atom  can 
have  no  states  ;  it  never  changes  ;  it  is  always  the  same.  But  con- 
sciousness is  always  some  particular  definite  state  ;  and  self-con- 
sciousness is  always  the  being  aware  of  some  particular  definite 
state.  There  is  no  consciousness  in  general ;  there  is  no  conscious- 
ness which  does  not  involve  change  of  state.  Indeed,  change  is  a 
reality  in  human  consciousness,  if  nowhei-e  else  in  the  universe  of 
being.  No  particular  state  of  consciousness,  whether  considered  as 
involving  an  attribution  of  that  state  to  a  subject  or  not,  could  be 
exjDlained  by  reference  to  the  material  nature  or  condition  of  such 
a  unit-atom. 

§  14.  The  foregoing  remarks  have  their  value  chiefly  as  a  warn- 
ing against  supposing  that  the  unity  of  the  soul's  real  being  suffers 
any  prejudice  because  it  is  not  to  be  regarded  or  explained  from  a 
point  of  view  furnished  by  physical  analogies.  To  be  one,  as  a  rigid 
material  atom  may  possibly  be  regarded  as  one,  would  be  no  ad- 
vantage to  the  soul.  Or  if  it  be  admitted  that,  in  case  it  had  such 
unity,  it  could  never  lose  its  real  being,  it  must  also  be  admitted  that 
we  are  unable  to  see  how  it  could  ever  gain  any  real  being  as  a  soul. 
Si  the  unit-atom  could  never  die,  it  could  also  never  live — as  a  con- 
scious psychical  existence.  And  it  is  the  unity  which  the  mind 
plainly  has  in  self-consciousness  that  is  alone  worth  contending  for. 
If  the  mind  were  really — that  is,  regarded  as  out  of  its  own  con- 
sciousness— one,  and  yet  two  or  more  in  consciousness,  it  would 
be  no  better,  but  rather  the  worse  off.  If  it  were  really  one,  but 
were  obliged  not  to  know  itself  as  one,  and  could  never  be  aware 
of  its  own  states,  or  attribute  them  to  the  one  "I"  which  is  the 
subject  of  them  all,  it  would  surely  be  the  worse  off.  To  be  one,  in 
the  only  meaning  of  the  word  that  is  of  real  value,  is  to  have  and 
to  keep  the  unity  of  consciousness.  If  this  unity  were  reaU}'-  a  mere 
seeming — a  trick  of  nature  to  cheat  the  mind — the  seeming  would 
forever  seem  real,  would,  indeed,  be  the  ground  of  all  reality  ;  the 
trick  would  be  the  kindest  of  all  illusions,  and  one  from  which  we 
should  crave  never  to  be  set  free.  When,  then,  we  have  recognized 
the  fact  that  aU  ordering  and  development  of  human  consciousness 


,    SEL>APPEAEANCE   OF   MIND.  687 

implies  this  kind  of  unit-being  as  belonging  to  the  mind,  we  have 
gone  as  far  in  vindication  of  the  mind's  rights  as  we  have  any  psy- 
chological interest  in  going. 

§  15.  That  the  mind  attributes  its  own  conscious  states  to  a  sub- 
ject of  such  states  (the  "  I "  in  all  sentences  such  as  "  I  think,"  "  I 
feel,"  etc.),  we  have  seen  it  necessary  to  admit  from  the  very  be- 
ginning of  our  psycho-physical  researches.  As  one  result  of  the 
study  of  perception  by  the  senses,  it  was  also  found  necessary  to 
recognize  a  certain  unifying  or  synthetic  activity  in  order  to  ac- 
count for  the  way  in  which  sensations  combine  to  form  the  "  pres- 
entations of  sense  ; "  such  unifying  activity  seems  plainly  to  imply 
the  existence  of  a  unit-being,  the  so-called  Mind.  Further  argu- 
ments in  the  same  direction  came  to  light  as  the  phenomena  of  the 
mind  in  memory,  voluntary  attention,  and  judgment  were  brought 
under  examination.  More  recently  still,  an  examination  of  the 
factors  of  self-consciousness,  from  the  more  purely  introspective 
point  of  view,  has  confirmed  the  same  opinion.  In  this  connection 
we  may  add,  finally,  the  argument  for  the  existence  of  the  mind  as 
a  real  unit-being,  which  has  been  so  forcefully  urged  by  one  of  the 
greatest  of  modern  psychologists  (Lotze).  The  mind  is  a  real  unit- 
being,  not  simply  because  it  appears  to  itself  to  be  such,  but  chiefly 
because  it  ai^pears  to  itself  at  all.  Granted  that  all  that  which 
only  appears  to  another  maybe  mere  seeming,  it  still  remains  indis- 
putable that  somewhat  appears.  The  somewhat  which  merely  ap- 
pears may  be  really  many  when  it  appears  as  one  ;  this  happens, 
in  some  sort,  in  the  case  of  all  "  Things  "  which  appear  many  or 
one  according  to  the  way  we  consider  them.  But  how  can  that  to 
which  all  else  appears,  whether  as  one  or  as  many,  and  that  which 
also  appears  to  itself — whether  it  appear  to  itself  as  one  or  as  many 
— really  be  other  than  one,  in  the  highest  sense  of  the  word  unity  ? 
No  twisting  of  imagination,  or  subtlety  of  argument,  can  show  how 
a  mind  not  really  one  could  appear  to  itself  at  all ;  or  break  the 
strength  of  the  conviction  inwrought  into  the  very  structure  of 
human  self-consciousness,  that  the  real  and  spiritual  being,  which 
we  call  Mind,  is  not  a  fortunate  confluence  or  phenomenal  centre 
of  changing  modes,  but  a  unit-being,  and  a  reason  of  all  unity  in 
whatever  becomes  the  object  of  its  thought. 

§  16.  As  to  the  first  and  last  things  of  the  Mind — its  origin  and 
destiny,  its  mortality  or  corruptibHity — Physiological  Psychology 
finds  itself  unable  to  pronounce.  It  cannot,  indeed,  explain  the  en- 
tire being  of  the  mind  as  arising  out  of  the  development  of  the 
physical  germ  fi'om  which  the  bodily  members  unfold  themselves. 
It  knows  no  decisive  reason  against  the  behef  that  such  a  non- 


688  THE   UNITY   OF   MIND. 

material  and  real  unit-being,  as  the  mind  is,  should  exist  in  other 
relations  than  those  which  it  sustains  at  present  to  the  structure  of 
the  brain.  On  the  contrary,  it  discloses  certain  phenomena  which 
at  least  suggest,  and  pei-haps  confirm,  the  possibility  of  such  exist- 
ence for  the  Mind.  But,  in  general,  if  it  remain  faithful  to  its  own 
mission,  within  its  own  limits,  it  entrusts  the  full  consideration  of 
these  questions,  after  it  has  cleared  the  way  from  barriers  of  igno- 
rance and  prejudice,  to  Eational  Psychology,  to  Ethics,  to  Meta- 
physics, and  to  Theology. 


INDEX. 


Agraphia,  nature  of,  294 

Allen,  Grant,  on  nature  of  feeling,  501  f., 

521 
Aphasia,  phenomena  of,  292  f . ;  kinds  of, 

394  f. 
Aqueduct  of  Sylvius,  88  ;  gray  matter  of, 

91 
Aqueous  Humor,  the,  173 
Arachnoid,  the,  structure  of,  63  f . 
Attention,    effect    of,    on    reaction-time, 

480  f.,  495  f.;  physical  basis  of,  538  f., 

542  f.;    effect    of,    on  perception   and 

memory,  539  f . 
Aubert,  on  measurement  of  light,  374  f. 
Automatic  Action,  nature  of,  49  f.,  130  f.; 

in  spinal  cord,  138  f. ;  and  brain,  144  f . ; 

physical  basis  of  volition,  535  f. 

Bain,  on  local  signs,  397  (note) ;  theory 
of  feeling,  501 ;  feeling  of  effort,  524 

Baxt,  on  reaction-time,  481 

Bechterew,  on  the  olivary  bodies,  150, 
161  f . ;  and  central  gray  matter,  161  f. 

Bell,  Sir  Charles,  discovery  of,  123  f . 

Ben  eke,  on  nature  of  feeling,  503 

Berger,  on  reaction-time,  478 

Bernstein,  on  exhaustion  of  nerves,  109. 

Betz,  "  giant- cells  "  of,  97,  283 

Birge,  E.  A.,  on  number  of  nervous  ele- 
ments, 46,  70  ;  excitability  of  cord,  143 

Blastoderm,  the,  300  £;  layers  of,  203  £; 
areas  of,  202  f. 

Blind-spot  {papilla  optica),  183 

Body,  general  relations  of,  to  mental 
phenomena,  560  f.;  early  development 
of,  563  f. ,  567 ;  phases  of,  565  f. ;  sexual 
differences  of,  570  ;  relative  proportions 
in,  571  f . ;  race-characteristics  of,  573  f . 

Brain,  chemistry  of,  25  f.,  27  f.;  mem- 
branes of,  61  f.;  structure  of ,  73  f.,  85 
44 


f.;  ventricles  of,  85,  149  f.;  ganglia  of, 
85  f.;  hemispheres  of,  91  f.;  lobes  of, 
92  f. ;  cortex  of,  95  f.;  inhibitory  in- 
fluence of,  143  f. ;  as  central  organ, 
143  f . ;  development  of,  204  f . ;  general 
functions  of,  239  f.;  temperature  of, 
243;  comparative  weight  of,  243  f.; 
weight  of  human,  244  f.;  relation  of,  to 
mind,  247  f.,  605  f.,  633  f.,  640  f. 

Broca,  convolution  of,  292  f, 

Briicke,  on  neutralization  of  taste,  403  ; 
perception  of  depth,  442 

Byasson,  on  brain-waste,  243 

Cameker,  on  measurement  of  taste, 
376  f. 

Capsule,  the  internal,  90,  91 

Carville  and  Duret,  on  stimulation  of 
motor  areas,  257 

Cattell,  on  reaction-time,  485,  493  f. 

Cells,  the  olfactory,  164f.;  the  gustatory, 
]67f.;  the  auditory,  193 

Central  Canal,  66  f . 

Cerebellar  tract,  71  f.,  75,  77 

Cerebellum,  74,  structure  of,  78  f.;  pe- 
duncles of,  79  ;  arbor  vitce  of,  79 ;  func- 
tions of,  153  f.;  lesions  of,  153  f. 

Cerebrin,  24,  35 

Cerebro-spinal  system,  axis  of,  62,  204  f . ; 
development  of,  204  f.,  213 

Cerebrum,  74,  82  ;  shape  of,  83 ;  gyri  of, 
84,  91  f.,95  ;  sulci  of,  84,  91  f.;  nervous 
elements  in,  91,  95  f . ;  layers  in  its  cortex, 
95  f. ;  fibres  of,  97  f . ;  nervous  paths  in, 
127  f.,  269  f.;  functions  of,  150  f.,  156 
f.,  239  f.;  development  of,  204  f.;  local- 
ization in,  239  f.,  250  f.,  255  f.,  269  f.; 
significance  of,  249  f . ;  effects  of  injury 
to,  258  f.,  269  f. 

Charcot,  scheme  of  decussation,  290 


690 


INDEX. 


Charcot  and  Pitres,  on  localization  of 
cerebral  function,  383 

Chaussier,  on  growth  of  foetus,  566 

Chemistry,  of  nervous  system,  21  f.,  217 
f . ;  of  cells  and  fibres,  28  ;  of  physio- 
logical function,  28  £,  111  1,  222;  of 
vision,  184  f. 

Chodin,  measuring  power  of  the  eye,  451 

Cholesterin,  23  f. 

Choroid,  the,  171  f. 

Clarke,  columns  of,  70 

Cochlea,  the,  191 

Color,  stimulus  of,  328  f.,  338  f.;  saturated, 
328 ;  tones  of,  329 ;  brightness  of,  330, 
376  ;  shades  of,  331  f . ;  complementary, 

333  f .,   343 ;    dependence   of,  on  time, 

334  f.;  and  place  of  the  retina,  335, 
388 ;  blindness  to,  335  f . ;  contrast  of, 
337,  460 ;  Young-Helmholtz  theory  of, 
338  f . ;  symbolism  of,  342  f . ;  sensitive- 
ness to,  375  f. 

Consciousness,  the  circuit  of,  494  f.; 
physical  basis  of,  544  f . ;  possibility  of 
a  prenatal,  565  f. ;  psycho-physical  ex- 
planations of,  596 ;  phenomena  of,  597 
f.;  unity  of,  607  f.,  631  f. 

Cornea,  structure  of,  171,  173,  175  f.; 
index  of  refraction  of,  176 ;  function 
of,  176  f. 

Corona  Radiata,  91 

Corpus  albicans,  83,  87 

Corpus  callosum,  82,  85 ;  function  of, 
98 

Corpus  dentatum,  of  the  medulla,  78 ;  of 
the  cerebellum,  79 

Corpus  geniculatum,  87,  89 

Corpus  quadrigeminum,  position  of,  87- 
structure  of,  90  f . ;  functions  of,  156  f . ; 
development  of,  208  f. 

Corpus  striatum,  86 ;  nuclei  of,  86  f . ; 
paths  in,  129;  functions  of,  '58f.,  160 
f.;  development  of,  208  f. 

Corpus  subthalamicon,  89 

Cortex  of  Cerebrum,  structure  of,  95  f . 

Crura  Cerebri,  83,  87;  crusta  and  teg- 
mentum of,  87  f.;  fibres  in,  87  f.;  func- 
tions of,  156 

Crusta,  see  Crura  Cerebri 

Crystalline  Lens,  the  structure  of,  173 

Deitebs,    processes  of,    43,  70;  conical 

hair-cells  of,  195,  197 
Dietze,  on  the  circuit  of  consciousness, 

4941 


Dobrowolsky,  on  measurement  of  color- 
sensations,  375  f . 

Donders,  on  localization  of  depth,  465; 
time  of  mental  processes,  468  f .,  479  f. 

Dove,  the  experiment  of,  442 

Drbal,  on  nature  of  feeling,  503 ;  kinds 
of  feeling,  505. 

Du  Bois-Reymond,  discoveries  of,  104, 
112,  115,  117 ;  theory  of  nervous  ac- 
tion, 227  f . 

Dura  Mater,  structure  of,  61  f . ;  processes 
of,  63. 

Eak,  185  f . ;  the  external,  185 ;  the  middle, 
186  f .  ;  bones  of,  187  f .  ;  tympanum  of, 
188 ;  vibrations  in,  188 ;  the  internal, 
189  f .  ;  vestibule  of,  189;  canals  of, 
189  f.  ;  cochlea  of,  191  ;  nerve  of,  191  f.  ; 
terminal  apparatus  of,  192  f.,  324; 
problem  of,  195;  development  of ,  211  f.; 
sensitiveness  of,  317,  319 

Ecker,  view  of  cerebral  cortex,  263 ; 
charts  of,  276  f . 

Eckhard,  law  of  central  mechanisms,  161 

Electricity,  "  current  of  rest  "  in  nerves, 
104,  106  f.,  117,  227  f.  ;  as  stimulus  of 
nerves.  111,  112,  114 f.,  228  f. ;  "nega- 
tive variation  "  in  nerves,  118,  227  f. 

Electrotonus,  Pfliiger's  law  of,  113, 115  f.; 
theory  of,  233  f.,  336  f. 

Embryo,  knowledge  of,  198  f.,  212  f.  ;  of 
the  fowl,  199  f.  ;  development  of ,  200  f., 
2041,  212  1,  618 

Encephalon,  see  Brain 

End-organs  of  Motion,  place  in  nervous 
system,  60,  164 ;  structure  of,  197 

End-organs  of  Sense,  place  in  nervous 
system,  60,  164  ;  significance  of,  1631; 
end-organs  of  smell,  164  f.  ;  of  taste, 
166  f.  ;  of  touch,  168  1 ;  of  sight, 
171  f.  ;  of  hearing,  185  f. 

Engelmann,  on  continuity  of  axis-cylin- 
ders, 40  f . 

Estel,  on  reaction-time,  490 

Eustachian  Tube,  186  1,  189 

Exner,  on  speed  of  reflex  action,  135 ; 
regio  olfactoria,  165 ;  nature  of  nerve- 
commotion,  234  f.  ;  general  function  of 
the  brain,  340 ;  cerebral  physiology, 
254,  367  ;  views  of,  on  localization,  267, 
279  f .,  384 1,  389  f.  ;  methods  of,  276  £  ; 
on  aphasia,  294;  reaction-time,  4701, 
480,  496  f . ;  attention.  538 

Eye,  structure  of,  171 1;  tunics  of,  171  f. ; 


INDEX. 


691 


refracting  media  of,  173  f.,  175  f. ;  ap- 
pendages of,  173  £,  177 ;  muscles  of, 
174  f.,  428  f.  ;  problem  of,  174  f.  ;  ad- 
justment of,  177  f.,  433 ;  pigments  of, 
184;  development  of,  210  f.;  motion  of, 
428  f.,  439  f. ;  meridians  of,  431  f.  ; 
torsions  of,  432  f.  ;  innervation  of, 
439  f .  ;  stereoscopy  of,  440  f. 

Fasciculus  Gracilis,  68,  73 

Fechner,  conception  of  psycho-physics, 
12 ;  on  measurement  of  sensation,  361  f., 
369  f. ;  lavi^  of,  365  f.,  374  f.,  594 

Feeling,  mixture  of,  in  local  signs,  398  f , ; 
of  innervation  or  effort,  415f.  ,5'73  f. ; 
of  "  double  contact,"  417  f.  ;  nature  of, 
499  f.,  504  ;  classes  of,  505  f. ;  intensity 
of,  508  f .  ;  tone  of,  509  f . ;  physical  ap- 
paratus of,  510  f .  ;  common,  512;  of 
sensation,  514  f. ;  the  emotions,  516  f., 
519  f.;  sthenic  and  asthenic,  518  f.  ;  the 
higher  aesthetic  and  intellectual,  520  f., 
523 

Ferrier,  on  corpora  quadrigemina,  157 ; 
and  striate  bodies,  159 ;  experiments  of, 
254,  264;  centres  of,  268  f.,  285  f.,  291 ; 
on  feeling  of  effort,  524 

Fick,  on  muscle-contractions,  119 ;  mi- 
nute color-sensations,  334  f.;  curve  of 
intensity,  475 

Filum  terminale,  64 

Fissures,  of  Sylvius,  92,  94,  210,  267  f.;  of 
Kolando,  92,  94,  267 

Flechsig,  on  tracts  in  spinal  cord,  71  f. 

Flourens,  on  respiratory  centre,  147  f . ;  op- 
tic lobes,  156 ;  localization  of  cerebral 
functions,  253 

Foramen  magnum,  64 

Formatio  reticularis,  in  the  medulla,  77 
f . ;  in  the  tegmentum,  88 

Foster,  on  the  respiratory  centre,  148 

Fovea  centralis,  183 

Franck  and  Pitres,  on  stimulation  of 
brain,  257 

Friedrich,  on  reaction-time,  483  f. 

Fritsch,  expeiiments  of,  253  f.,  264 

Frohlich,  classification  of  sensations  of 
smell,  310 

Funke,  on  Weber's  "sensation-circles," 
407 


Gall,  on  cerebellum,  156 ;  phrenological 

theory  of,  252 


Gamgee,  on  chemistry  of  brain,  35  f . 

Ganglia,  the  "basal,"  88  f. 

Ganglion-cell,  see  nerve-cells 

George,  theory  of  temperament,  575  f. 

Gerlach,  on  intimate  structure  of  the 
cord,  70 ;  and  cerebral  cortex,  96 

Gliky,  on  nerve-tracts,  261 

Goldscheider,  on  "  pressure  spots,"  346 
f.,  369,  410;  temperature-spots,  348  f., 
370,  413 

Goll,  column  of  (see  fasciculus  gracilis) 

Goltz,  experiments  of,  on  spinal  cord,  140; 
on  optic  lobes,  157 ;  view  of  localiza- 
tion, 264  £,  273  f.;  experiments  of, 
297  f. 

Griitzner,  on  nature  of  nerve-commotion, 
225  f. 

Gyri  (or  convolutions)  of  the  cerebrum, 
84,  92,  93  f.;  development  of,  210 

Hall,  G.  Sta?«ley,  on  perception  of  mo- 
tion, 411  f.,  416 ;  studies  of  rhythm, 
490 

Hamilton,  on  the  circuit  of  consciousness, 
494 ;  tone  of  feeling,  509 

Hearing,  end-organ  of,  185  f.;  sensations 
of,  195,  315  f.;  perceptions  of,  403  f. 

Helmholtz,  on  speed  of  nervous  processes, 
120  f.;  index  of  refraction  of  cornea, 
176;  accommodation  of  eye,  177  f., 
433  ;  size  of  blind-spot,  183  f . ;  analysis 
of  sound,  196;  nature  of  noises,  316; 
consonances  of  tone,  323  f.;  theory  of 
color-sensations,  338  f . ;  and  of  percep- 
tion, 389  f. ,  452 ;  on  Listing's  law,  431 ; 
movements  of  the  head,  454  ;  localiza- 
tion of  depth,  465 

Hensen,  on  function  of  labyrinth,  194  f., 
196;  nature  of  noises,  316 

Hering,  theory  of  color-sensations,  340  f. ; 
of  tem'perature-sensations,  350  f.;  in- 
nervation of  the  eye,  439  f.,  451,  525; 
movements  of  the  head,  454 

Hermann,  on  electrical  phenomena,  in 
nerves,  118  f.,  120;  theory  of  nervous 
action,  226  f. 

Herschel,  on  brightness  of  stars,  373  f. 

Herzen,  on  sensations  of  temperature, 
352  f. 

Hill,  A.,  view  of  "  basal  ganglia,"  89 

Hirsch,  on  reaction-time,  470 

Hitzig,  experiments  of,  253  f.,  264;  on 
localization  of  cerebral  function,  253  f., 
267 ;  centres  of,  367  f . 


692 


INDEX. 


Horopter,  calculation  of,  437 
Horwicz,  theory  of  feeling 

Inhibition,   nature    of,    51,   144;    from 

brain  on  cord,  143  f. 
Iris,  the,  172 
Island  of  Reil,  93 ;  layers  in,  97 ;  function 

of,  295  f . 

James,  Professor,  theory  of  the  emo- 
tions, 519  f.;  on  the  feeling  of  effort, 
524  f. 

Jastrow,  on  comparative  judgments  of  eye 
and  hand,  466  ;  studies  of  rhythm,  490 

Kant,  on  sthenic  and  asthenic  feeling, 
518  f. 

Keppler,  on  measurement  of  taste,  377 

Klug,  on  localization  by  temperature,  414 

KoUiker,  on  end-organs  of  touch,  170 

KoUert,  on  reaction-time,  489  f . 

Kraepelin,  on  measurement  of  visual  sen- 
sations, 375 

Krause,  end-bulbs  of,  169  f.;  on  index  of 
refraction,  176 

Kuhne,  on  chemistry  of  retina,  28, 184  f . ; 
function  of  nerve-fibres,  54 ;  structure 
of  end-plates,  197 

Kunkel,  on  inertia  of  the  retina,  474 

Kussmaul,  on  aphasia,  393 

Lamanskt,  on  measurement  of  color- 
sensations,  375 

Lecithin,  36  f . 

Le  Conte,  on  Listing's  law,  431,  439; 
torsions  of  the  eye,  431  ;  nature  of  the 
horopter,  437  f.  ;  theory  of  double 
images,  443 

Listing,  the  law  of,  430  f.,  439 

Lobes,  of  the  cerebrum,  92  f. 

Local  Signs,  theory  of,  387  f.,  396  f.,  398 
f.,  409 

Lob,  on  visual  areas,  388  f. 

Lohmeyer,  on  cases  of  aphasia,  296 

Lombard,  on  temperature  of  brain,  242 

Longet,  on  columns  of  the  cord,  125  f.  ; 
localization  of  cerebral  function,  253  f. 

Lotze,  theory  of  local  signs,  387,  396  f., 
451 ;  on  distinctions  by  the  skin,  409 ; 
perception  of  magnitude  by  the  eye, 
451  ;  errors  of  sense,  455 ;  theory  of 
feeling,  499  f.,  510;  image  of  memory, 
547  f.;  differences  of  the  sexes,  573; 
kinds  of  temperament,  577  f. 


Luchsinger,  on  reflexes  of  the  cord,  138, 
141 

Luciani,  on  localization  of  cerebral  func- 
tion, 369  f.,  385,  288,  301 

Luys,  on  basal  ganglia,  129 ;  attention 
and  will,  544 ;  memory,  553. 

Mach,  on  fusion  of  nervous  shocks,  473 

Magendie,  discovery  of,  123  f. 

Materialism,  views  of,  607  f . 

Matteucci,  on  electrotonus,  338 

Mechanism,  nervous  system  as,  4  f.,  19f., 
198,  314  f.;  the  nerve  as,  104;  develop- 
ment of,  198 ;  theory  of  the  nervous, 
214  f.,  223  f.,  226  f. 

Medulla  Oblongata,  structure  of,  74  f.; 
tracts  of  white  matter  in,  76  f. ;  gray 
matter  in,  77  f.;  nuclei  of,  78;  reflex- 
motor  functions  of,  146  f. ;  as  auto- 
matic, 147  f.;  centres  of,  147  f.,  150; 
vaso-motor  function  of,  148 

Meissner,  calculation  of  the  horopter, 
437  f. 

Membranes,  of  the  brain,  63  f.;  the  bas- 
ilar, of  Reissner,  191 ;  Kolliker,  194 

Memory,  reproduction  of  images  of,  491 
f.,  54t)  f. ;  physiological  study  of,  535  f.; 
physical  basis  of,  545  f.,  550  f. ;  as  re- 
tentive, 548  f.;  the  organic,  550  f.;  as 
reproductive,  553  f . ;  psychological  nat- 
ure of,  554  f . 

Merkel,  on  reaction-time,  483  f.,  486, 
495  f . 

Mesencephalon,  development  of,  307  f . 

Meynert,  description  of  brain,  73,  98  f., 
246;  on  layers  of  cerebral  cortex,  95; 
relation  of  brain  to  intelligence,  348 ; 
nerve-tracts  in  cerebrum,  283 

Mind,  subject  of  phenomena,  3  f.,  585  f., 
596  f . ;  relation  to  nervous  mechanism, 
235  f.,  560  f.,  579  f.;  and  to  the  brain, 
247  f.,  588  f.,  593  f.,  605  f.,  633  f.;  syn- 
thetic act  of,  in  perception,  388  f.,  416 
f.,  463  f.,  467,  594  f.;  faculties  of,  5S7 
f.,  600  f.;  physical  explanations  of,  593 
f.,  603  f.,  635  f.;  as  a  unit-being,  596  f., 
668  f.,  683  f.;  phenomena  of,  597  f.;  as 
a  real  being,  606  f.,  611,  633  f.,  656, 
668  f.;  development  of,  614  f.,  633  i; 
seat  of,  634  f . ;  physical  organs  of,  640 
f.;  as  a  cause,  648  f. ;  spirituality  of, 
681  f. 

Moldenhauer,  on  reaction-time  of  tast^ 
479 


INDEX'. 


693 


Moos,  on  duration  of  the  image  of  mem- 
ory, 549 

Motions,  the  Bodily,  classes  of,  526  f.;  the 
impulsive,  5'37 ;  the  voluntary,  527  f., 
530  ;  the  expressive,  531 

Mtiller,  G.  E.,  on  measurement  of  sensa- 
tions, 368 

Muller,  J.,  on  brain  as  measure  of  intelli- 
gence, 248 

Munk,  experiments  of,  370  f.;  on  localiza- 
tion of  cerebral  function,  272  ;  motor 
areas  of,  272  f. ;  visual  areas  of,  286  f.; 
auditory  area  of,  291 

Nahlowsky,  on  nature  of  feeling,  503 ; 
kinds  of  feeling,  505  f. 

Nerve-ceUs,  chemistry  of,  28 ;  elements  of 
nervous  system,  30  f.  ;  kinds  of,  31  f. ; 
intimate  structure  of,  42  f . ;  shapes  of, 
44  f. ;  processes  of,  44,  70  ;  size  of,  45  ; 
as  a  typical  element,  45  f . ;  number  of, 
46;  functions  of,  49  f.,  134,  234  f.;  of 
the  embryo,  300  f.,  213 

Nerve-commotion,  causes  of,  48 ;  condi- 
tions of,  106  f.,  132;  phenomena  of, 
111  f.,  230;  nature  of,  116  f.,  122, 
222;  laws  of,  118  f.,  122,  230;  speed  of , 
130  f.,  123  f.  ;  paths  of,  123  f.,  127  f., 
261,  283  ;  summation  of,  223  f.,  233  f.  ; 
facilitation  of,  224  £ 

Nerve-fibres,  chemistry  of,  28 ;  ele- 
ments of  nervous  system,  30  f.  ;  kinds 
of,  34  f . ;  size  of,  34,  41  f.  ;  structure  of 
the  medullated,  35  f.  ;  fibrillated  axis- 
cylinder  of,  38  £. ;  origin  of,  45  f.  ; 
number  of,  46  ;  in  the  cord,  68  f.,  123  f., 
134 ;  of  the  embryo,  212 

Nerve-muscle  machine,  104  f.  ;  behavior 
under  electricity,  111  f .  ;  as  a  mechan- 
ism, 215  f. 

Nerves,  structure  of,  33  f . ;  general  func- 
tion of,  47  f.,  54,  59  f.,  106  f.  ;  excita- 
bility of,  47,  106  f.,  353  f.;  conductivity 
of,  47,  60,  102-122,  118  1,  120;  kinds 
of,  51  f.,  60,  353  f.;  aflferent,  52  f.,  120  ; 
efferent,  53  f.,  120;  the  cranial,  100  f.; 
the  encephalic,  100  f.  ;  exhaustion  of, 
108  f.;  mechanical  properties  of,  109; 
thermic  influences  upon,  110  f.;  chemi- 
cal influences  on.  111  ;  processes  in, 
117  f.;  specific  energy  of,  300  f.,  307  f,, 
353  f. 

Nervous  Matter,  kinds  of,  23  f . ;  specific 
gravity  of,  23  f. 


Nervous  System,  a  mechanism,  4  f. ,  19£, 
198  f.,  314  f.,  233  f . ,  236  i ;  general  func- 
tion of,  181,  .57,  2191;  elements  ol  31 
1,301,  2161;  chemistry  of,  211,3171; 
cells  and  fibres  in,  30  f . ;  structure  of, 
56-101 ;  plan  of,  57  1,  219  1  ;  sets  of 
organs  in,  59  1;  the  sympathetic,  60  f.; 
the  cerebro-spinal,  60  f . ;  development 
of  the,  198  1;  inertia  of,  473  f. 

Neuclein,  24  f . 

Neuroglia,  nature  of,  31  f. 

Neurokeratin,  24 

Nothnagel,  on  striate  bodies,  159 ;  fine- 
ness of  temperature-sense,  369  f . 

Nuclei  of  nerve-cells,  43  ;  of  the  medulla, 
78 ;  of  the  corpus  striatum,  86,  88,  90, 
159  ;  of  the  tegmentum  (red  nucleus), 
88,  89 

Nystagmus,  153  1 

Olives,  the,  75,  78 ;  functions  of,  150 

Optic  Thalami,  position  of,  86  f . ;  struct- 
ure of,  89  1;  connections  of,  90,  1271; 
cells  and  fibres  of,  90 ;  paths  in,  129 ; 
functions  of,  158  f.  ;  development  of, 
2081 

Organ  of  Corti,  193  1 

Organs,  kinds  in  nervous  system,  59  f.  ; 
the  central,  60,  73  f.  ;  functions  of, 
130  f .,  224  f . 

Ott,  on  centre  of  temperature,  161 

Pacini,  corpuscles  of,  169 

Paneth,  on  excitation  of  cerebral  cortex, 
2691 

Papillse,  circumvallatae,  166  f. ;  fungi- 
formes,  166  f . 

Peduncles,  of  the  cerebellum,  79 ;  of  the 
cerebrum,  82,  87  1 ,  97  1 

Perception,  nature  of,  383  f.,  4621,  467, 
538  1;  nativistic  and  empiristic  the- 
ories of,  389  1;  by  smell,  403  1;  taste, 
403;  hearing,  403  f.;  touch,  405  1;  of 
motion,  411  1,  453  1;  by  temperature, 
413  1;  of  sight,  421  1,  440  1,  448  1; 
of  depth,  441  1,  459,  464;  of  spatial 
relations,  448  1,  464  1;  development 
of,  462  1 ;  physical  basis  of,  538  f . 

Pfluger,  table  from,  113;  law  of,  113  1, 
115  ;  on  reflexes  of  the  cord,  137  f. 

Physiological  Psychology,  definition  of, 
1  1,  4  1;  combines  two  sciences,  6  1; 
divisions  of,  8  1;  method  of,  9  1,  12, 
532  ;  claims  of,  13  ;  successes  of,  304  f ., 


694 


INDEX. 


532  f.,  592  f. ;  theory  of  perception  of, 
382  f.;  limits  of,  532  f. 

Physiology,  relation  to  psychology,  1  f.; 
of  nerves  in  general,  103  f. 

Pia  Mater,  structure  of,  64 

Pons  Varolii,  74  ;  structure  of,  81  f. 

Presentations  of  Sense,  elements  of,  304 
f.,  383  f.,  468  f.;  process  of  construc- 
tion of,  382  f.,  387  f.,  416  f.,  448  f.; 
space-form  belonging  to,  385  f . ,  391  f . , 
448  f;  synthesis  of,  386  f.,  416  f.,  467; 
analysis  of,  388  f.,  595 ;  nativistic  the- 
ory of,  389  f. ;  empiristic  theory  of,  389 
f.;  stages  of,  400  1;  by  smell,  402  f.; 
taste,  403  ;  hearing,  403  f . ;  by  touch, 
405  f.;  by  sight,  421  f.,  433  f.,  443  f.; 
time-relations  of,  468  f.;  assumptions 
entering  into,  594 

Pressure,  sensations  of,  345  f.,  367  f.; 
spots  of,  346 

Preyer,  on  sensitiveness  to  pitch,  319  f.; 
fusion  of  nervous  shocks,  472;  sensa- 
tions of  new-born  child,  569 

Protagon,  25  f. 

Psychology,  conception  of,  2  f.;  method 
of,  9  f.,  587  f.,  605  f. ;  classifications  of, 
5871,  605  f. 

Psychometry,  method  of,  469  f.;  elements 
of  time  in,  470  f . ;  results  of,  497 

Psycho-physics,  Fechner's  conception  of, 
12,  380  f.;  method  of,  359,  361  f..  365 
f.;  the  laws  of,  359  f.;  365  f.;  379  1; 
of  sensations  of  touch,  367  f . ;  •  of  sound, 
370 ;  of  light,  373  f.;  of  smell  and  taste, 
376  f. 

Purkinje,  cells  of,  80 

Pyramidal  tract,  71  f.,  77,  97 

QuETELET,  proportions  of  human  body, 
566  f.,  574 

Ranvier,  nodes  of,  36  f.,  40  f. ;  on  struct- 
ure of  ganglion-cell,  43 

Reaction -time,  nature  of,  475  f.;  influ- 
ences upon,  476  f.,  495  f. ;  methods  of 
determining,  479  f.;  complex  processes 
of,  491 

Reflex  action,  50  1,  130  f.;  kinds  of,  131  ; 
in  spinal  cord,  131  1, 136  f.;  conditions 
of,  134  f.,  1361;  speed  of,  135  f.;  in  the 
brain,  143  f.,  224  f. 

Regio  olfactoria,  164  f.,  308  f. 

Reissner,  membrane  of,  191 

ilemak,  fibres  of,  34,  41 


Retina,  the,  172  f.;   problem    solved  by 
174  f.,  178  f.,  183  f.;  layers  of,  179  f., 
183  f.;  nervous  elements  of,  180  f. ,  32ti 
f. ;  rods  and  cones  in,  181  f.,  327  ;  own 
light  of,  326  ;  relation  of,  to  sight,  335, 
423  f.;  field  of,  423  f.;   identical  and 
corresponding  points  of,  434  f . 
Ribot,    on    physiological   study   of  con- 
cepts, 532 ;  and  of  memory,  552  f . 
Ritter,  on  sensations  of  smell,  309 
Rolando,  funiculus   of,  77 ;    tubercle  of, 

77  ;  fissure  of,  92,  267,  282 
Romieu,  on  stimulus  of  smell,  311 
Rosenthal,  on  speed  of  reflex  action,  135 
f.;  electrical  taste,  313 

SCHAFHADTL,  on  limits  of  sound,  372  f. 

SchifF,  on  posterior  columns  of  cord,  125 
f. ;  on  excitability  of  cord,  141  f. ;  on 
cerebellum,  153,  155  f.;  temperature  of 
brain,  242 ;  localization  of  cerebral 
function,  273  f.,  283  f. 

Schultze,  Hans,  on  structure  of  axis- 
cylinder,  39  f. 

Schultze,  Max,  on  varieties  of  nerve- 
fibres,  34  f.;  and  structure  of  nerve- 
ceU,  42  f.;  on  olfactory  cells,  164  f.; 
auditory  cells,  192 

Schwann,  sheath  of,  36  ;  substance  of,  36 

Sclerotic,  the,  171 

Seguin,  on  cases  of  aphasia,  295 

Semicircular  canals,  the,  189  f. 

Sensations,  end-organs  of,  164  f.;  analysis 
of  auditory,  195,  324 ;  quality  of,  303  f., 
325  f.;  simple,  305  f. ;  conditions  of, 
307  f.;  of  smell.  308  f.,  376  f.;  of  taste, 
311  f.,  376  f.;  of  sound,  315  f.,  370  f.;  of 
sight,  325  £,  373  f.;  theory  of  the  vis- 
ual, 338  f . ;  of  temperature,  344,  369  f. ; 
of  pressure,  314,  345  f.,  367  f.;  the  mus- 
cular, 344  f . ;  quantity  of,  356  f . ;  meas- 
urement of,  359  f.,  364  f.,  369  f.;  least 
observable  difference  in,  361  f.,  364  f.; 
range  of,  362  f . ;  spatial  series  of,  386  f ., 
393  f.;  localization  of,  387  f.,  405  f. 

Senses,  organs  of  the,  164  f.;  classifica- 
tion of  the,  303  f . ;  the  geometrical,  386 
f. ;  errors  of  the,  455  f . 

Setschenow,  on  inhibitory  centres,  144. 

Sight,  end-organs  of,  171  f.,  174  f.,  338  f. 
photo-chemistry  of,  178  f.,  184  f.,  326 
sensations  of,  335  f.;  stimulus  of,  325  f. 
after-images  of,  336  f . ;  elements  m  per- 
ception of,  420  f.,  447  f.;  motion  of  eye 


INDEX. 


695 


in,  428,  431  f . ;  single  and  double  images 
in,  434  f . ,  438  f . ;  stereoscopic  and  per- 
spective, 440  f. ;  secondary  helps  of,  443 
f.,  455  t 

Smell,  organs  of,  164  f . ,  308  f . ;  nerve  of, 
165,310;  stimulus  of,  165  f.,  308  f., 
310 ;  sensations  of,  308  f . ;  kinds  of, 
310  ;  measurement  of,  378  f . ;  percep- 
tions of,  403  f . 

Soul,  see  Mind 

Sound,  analysis  of,  195  f.,  324;  sensa- 
tions of,  315  f.,  370  f.;  kinds  of,  316; 
nature  of  the  musical,  316  f . ;  limits  of, 
317,  371  f;  "entotic,"403f.;  direction 
of,  404 

Spinal  cord,  membranes  of,  61  f . ;  struct- 
ure of,  64  f .,  143,  207  ;  fissures  of,  64  f.; 
columns  of,  66,  67,  135  f.;  commissures 
of,  66 ;  horns  of,  67 ;  white  substance 
of,  68;  nerve-fibres  in,  68  f.,  133  f.; 
gray  substance  of,  69  f . ;  nervous  tracts 
in,  71  f.,  133  f.;  as  mechanism,  73,  123, 
133  f.,  144;  nerves  from,  100  f. ;  nervous 
processes  in,  122, 134  f.;  roots  of,  123  f., 
207;  as  a  central  organ,  133  f.,  138  f. ; 
automatism,  138  f. ;  "centres"  of,  140 
f. ;  excitability  as  a  whole,  141  f.;  ''  £es- 
thesodic"  and  "  kinesodic,"  142;  in- 
fluence of  brain  on,  143  £ ;  develop- 
ment of,  207 

Stimulus,  kinds  of,  48;  heat  as,  110  f.; 
electricity  as,  111  f.,  312  f. ;  of  smell, 
165  f.,  308  £,  376  f.;  of  taste,  311  f., 
376  f.;  of  hearing,  315,  370  f.;  of  sight, 
335  f . ,  338  £ ,  373  f . ;  measurement  of, 
359  £,  367  £;  limits  of,  363  £,  367  £ 

Strabismus,  153  f . 

Strieker,  on  common  feeling,  513 

Stumpf,  on  judgment  of  tone,  330 

Substantia  gelatinosa,  69 

Substantia  nigra,  87 

Sulci,  of  the  cerebrum,  84,  91,  93  £;  de- 
velopment of,  210 

Sully,  on  tone  of  feeling,  511 

Suspensory  ligament,  173;  function  of, 
177  £ 

Sympathetic  System,  structure  of,  60  f. 

Talbot,  the  principle  of,  473 

Taste,  end- organs  of,  166  f.,  313;  nerve 
of,  168,  314;  sensations  of,  311  f., 
376  f.  ;  stimulus  of,  313  f.  ;  kinds  of, 
314;  measurement  of,  376  £  ;  percep- 
tions of,  403  £ 


Tegmentum,  see  Crura  Cerebri 
Temperament,    theory    of,    575  £,   579; 

kinds  of,   575  £  ;    physical   basis    of, 

579 
Temperature,   sensations  of,  344,  348  £ , 

369  £ ;  after-images  of,  351  £ ;  measure- 
ment of,  369  £  ;  sense  of  locality  by, 
413  £ 

Thalamen-cephalon,  208 

Things,  distinguished  from  sensations, 
359  f . ,  382,  594  ;  results  of  mental  syn- 
thesis, 594  f.,  609  ;  unity  of,  609  £ 

Thudichum,  on  chemistry  of  brain,  27 

Tischer,  on  Weber's  law,  373 

Tones,  the  musical,  316;  pitch  of,  317  f.; 
table  of,   318 ;    sensitiveness   to,    319, 

370  £;  purity  of,  319  £  ;  judgments  of, 
320  ;  relations  of,  322  f . 

Touch,  kinds  of,  168,  345  £  ;  end-organs 

of,  168  f.  ;   sensations  of,  345  £,  367  £; 

perceptions  of,  405  £ ;  the  field  of,  406 

£,  416  £ 
Trautscholdt,    reaction-time  of  complex 

processes,  491  f.;  on  effect  of  practice, 

496 
Turck,    method  of,    71 ;  on   columns  of 

cord,  126 
Tympanum,  the,  186  f.  ;  membranes  of, 

186,  188  f . ;  windows  of,   186 ;  muscles 

o£  187  ;  office  o£  187  £ 
Tyndall,  on  stimulus  of  smell,  311  f. 

Valentin,  on  nervous  excitation,  233  £ ; 
sensations  of  smell,  308  f.  ;  of  taste, 
314,  377  £ ,  403  ;  on  sense  of  locality, 
406  £ ;  fusion  of  nervous  shocks,  473 

Valli,  principle  of,  107 

Vestibule,  of  the  ear,  189 

Vierordt,  on  measurement  of  sensation, 

371  f .  ;  localization  by  touch,  409  f.  ; 
subjective  estimate  of  time,  488  £ 

Vitreous  Humor,  the,  173 

Volkmann,  A.  W.,  on  measurement  of 
sound,  371 ;  of  light,  374 ;  of  length  of 
lines,  376;  on  sense  of  locality,  407 

Volkmann  von  Volkmar,  on  motifs  of 
monocular  vision,  430;  nature  of  feel- 
ing, 503 

Volta,  on  electrical  taste,  313  £ 

Von  Gudden,  on  optic  chiasm,  390 

Von  Kries,  on  the  number  of  colors,  333 ; 
on  theories  of  color-sensations,  341  £; 
sense  of  locality,  397 

Von   Kries   and  Auerbach,  on  sense  of 


696 


INDEX. 


locality,  397;  reaction- time,  476,  481  f., 
487,  496 

Von  Vintschgau,  on  conduction  in  nerves, 
121  ;  reaction-time  for  multiplying,  493 

Von  Wittich,  on  fusion  of  nervous  shocks, 
472  ;  reaction-time  of  taste,  478 

Vulpian,  on  nervous  function,  54  ;  on  ex- 
citability of  cord,  142 ;  centres  of  the 
medulla,  149  ;  and  cerebellum,  154  f. 

Wagner  (H.  and  R.),  corpuscles  of,  170; 
on  measurement  of  brain-mass,  247 ; 
effect  of  fear,  518 

Waller,  method  of,  107  f. 

Weber,  E.  H.,  on  temperature-sensations, 
110,  347,  351 ;  smell,  308 ;  law  of,  365 
f.,  368  f.,  374  f.,  378  f.;  on  direction  of 
sound,  404  ;  perceptions  of  touch,  405 
f.;  "sensation-circles"  of,  406  f.; 
measuring  power  of  the  eye,  452 


Wertheim,  on  ductility  of  nerves,  109 
Will,  effect  of,  on  bodily  motions,  528  f.; 
physiological  study  of,  535  f . ;  physical 
basis  of,  536  f . ;  in  attention,  539  f . 
Wundt,  on  columns  of  the  cord,  126 ;  on 
cerebellum,  152  ;  optic  thalami,  158  f . ; 
and  striate  bodies,  160 ;  mechanical 
theory  of,  231  f.;  kinds  of  taste,  314; 
theory  of  color-sensations,  341 ;  on  com- 
plementary colors,  343 ;  theory  of  apper- 
ception, 380,  539  f.;  on  Weber's  law, 
381  ;  on  theories  of  perception,  389  f.; 
''sensation-circles,"  408 ;  visual  percep- 
tion, 422,  425  f.,  451 ;  judgment  of 
distance,  433 ;  feelings  of  innervation, 
439,  451,  524 ;  psycho-physical  time, 
471,  477,  483  f.,  488,  496  ;  curve  of  feel, 
ing,  514  ;  theory  of  temperament,  576  f, 

Zonule  of  Zinn,  173 


THE 


Philosophical  Works 

OF 

GEORGE  TRUMBULL  LADD 

Professor  of  Philosophy  in  Yale  University 


GENERAL 

DESCRIPTIVE 

PSYCHOLOGY 


Psychology :  Descriptive  and  Explanatory 

8vo.     $4.50 

Primer  of  Psychology 

i2mo.      $1.00  nei 


PHYSIOLOGICAL 
PSYCHOLOGY 


Elements  of  Physiological  Psychology 

With  Numerous  Illustrations.     8vo.     $4.50 

Outlines  of  Physiological  Psychology 

Illustrated.     8vo.     $2.00 


METAPHYSICAL 
PSYCHOLOGY 


Philosophy  of  Mind 


5VO.       $3.00 


Philosophy  of  Knowledge 

8vo.     $4.00 


NOTE.— The  philosophic  writings  of  Dr.  Ladd  have  now  become  so  numerous  and 
are  so  widely  known  in  a  general  way,  that  the  publishers  take  pleasure  in  giving  them 
some  special  notice,  with  the  object  that  the  adaptation  and  purpose  of  each  volume  may 
be  better  understood.  It  is  believed  that  this  author's  "Primer  of  Psychology," 
"  Psychology  :  Descriptive  and  Explanatory,"  "  Elements  of  Physiological  Psychology," 
and  "  Philosophy  of  Mind  "  form  a  continuous  course  in  the  subject  which  surpasses  any 
similar  course  that  has  appeared.  Naturally,  where  several  books  by  one  author  treat  of 
the  same  subject,  some  confusion  in  ordering  results,  and  it  is  to  prevent  this,  as  well  as 
in  the  hope  of  leading  to  a  wider  interest  in  the  books,  that  the  following  description  has 
been  prepared. 


J  GENERAL   DESCRIPTIVE  PSYCHOLOGY 


PSYCHOLOGY:     DESCRIPTIVE    AND    EXPLANATORY 

A  Treatise  of  the  Phenomena,  Laws  and  Development  of  Human  Mental  Life 
8vo.    676  pages.    $4.50 

As  indicated  in  the  sub-title,  this  work  has  for  its  object  the  study  of 
human  mental  life,  and  is  perhaps  better  defined  by  the  term  introspective 
psychology  than  by  any  other  in  common  use.  It  is  a  general  treatise 
for  those  who  wish  to  gain  a  thorough  knowledge  of  the  subject,  not  de- 
signed merely  for  use  as  a  text-book,  while  at  the  same  time  the  product 
of  one  who  has  taught  a  large  number  of  pupils,  and  embodying  much 
experience  gained  through  the  work  of  the  class-room.  The  size  and 
scope,  the  amount  and  kind  of  material,  and  the  style  of  its  presentation 
unite  in  making  it  a  suitable  book  for  mature  students,  as  those  usually 
are  who  begin  the  subject  in  colleges.  It  is  therefore  a  college  text-book, 
and  is  recommended  without  qualification  for  such  use. 

"  Professor  Ladd  has  presented  in  this  work  a  great  body  of  facts  on  all  the  important 
points  in  psychology,  and  has  subjected  them  to  a  keen  and  illuminating  criticism.  I  know 
of  no  other  work  that  gives  so  good  a  critical  survey  of  the  whole  field  as  this." 

— Prof.  B.  P.  BowNE,  Boston  University. 

"  It  is  rich  in  material,  admirably  clear  and  well  arranged,  and  a  thoroughly  satisfac- 
tory introductory  book  for  the  student  in  this  rapidly  developing  field  of  study.  I  shall 
at  once  recommend  its  use  by  my  classes." 

— Prof.  J.  W.  Stearns,  University  of  Wisconsin. 

"  My  impression  of  it  is  that  it  is  Professor  Ladd's  best  work,  that  it  contains  the 
maturest  and  most  independent  expression  of  his  views  on  all  the  principal  topics  in 
psychology.    It  is  a  distinct  honor  to  American  scholarship  to  have  produced  it." 

—Prof.  H.  N.  Gardner,  Smith  College. 


PRIMER   OF    PSYCHOLOGY 

i2mo.    226  pages.    $1.00  net 

As  its  title  indicates,  this  is  a  text-book  for  elementary  students,  and 
was  written  by  this  eminent  author  because  no  book  in  America  had  been 
found  satisfactory  for  academies  and  high  schools,  and  for  a  large  class 
of  general  readers  who  might  find  some  pleasure  and  perhaps  more 
profit  in  reading  a  very  brief  and  very  simple  treatise  on  psychology. 
The  author's  success  in  his  undertaking  may  be  measured  by  the  fact 
that  within  eighteen  months  of  its  publication  six  editions  were  ex- 
hausted. The  book  will  be  used  the  coming  year  in  more  than  sixty 
high  schools  and  academies,  as  well  as  in  many  colleges  and  normal 
schools, 

CONTENTS: 

I.  The  Mind  and  Its  Activities.  VII.  Hearing  and  Sight. 

II.  Consciousness  and  Attention.  VIII.  Memory  and  Imagination. 

III.  Sensations.  IX.  Thought  and  Language. 

IV.  Feeling.  X.  Reasoning  and  Knowledge. 

V.    Mental  Images  AnD  Ideas.  XI.    Emotions,  Sentiments  and  Desires. 

VI.    Smell,  Taste  and  Touch.  XII.    Will  and  Character. 

XIII.    Temperament  and  Development. 


'PHYSIOLOGICAL  PSYCHOLOGY 


ELEriENTS   OF   PHYSIOLOGICAL   PSYCHOLOGY 

A  Treatise  of  the  Activities  and  Nature  of  Mind  from  the  Physical  and  Experimental 
Point  of  View.    With  numerous  illustrations.    8vo,  $4.50 

In  distinction  from  the  introspective  psychology  and  as  a  companion 
to  it  this  book  is  devoted  to  physiological  and  experimental  psychology. 
By  its  proportions  and  subject  matter  it  is  adapted,  like  the  other  book, 
to  mature  students,  and  is  of  equal  interest  to  general  readers  as  well  as 
to  specialists  in  this  field.  It  was  the  first  book  in  English  to  discuss  the 
whole  subject,  and  is  the  only  one  which  may  be  regarded  as  an  adequate 
treatise.  It  includes  the  latest  discoveries,  and  by  numerous  excellent 
illustrations  and  tables,  and  by  gathering  material  from  an  immense 
number  of  sources  inaccessible  to  most  persons,  it  brings  before  the  stu- 
dent in  the  most  lucid  form  the  entire  subject.  The  most  competent 
critics  pronounce  it  a  credit  to  America's  scholarship  and  an  unrivalled 
authority.  Without  reserve  it  is  recommended  as  a  text-book  for 
advanced  study. 

"  His  erudition  and  his  broad-mindedness  are  on  a  par  with  each  other ;  and  his  vol- 
ume will  probably,  for  many  years  to  come,  be  the  standard  work  of  reference  on  the 
subject."— Prof.  William  James  in  The  Nation. 

"  He  writes  at  once  as  a  scientist  bent  on  gaining  the  fullest  and  clearest  insight  into 
the  phenomena  of  mind,  and  as  a  metaphysician  deeply  concerned  with  the  sublime 
question  of  the  nature  of  the  spiritual  substance." — James  Sully  in  The  Academy. 

"  Professor  Ladd's  noble  book  is  in  the  interest  of  true  science,  of  sound  theology,  of 
real  religion.  We  commend  it  in  the  highest  terms,  both  to  physiologists  and  to  psychol- 
ogists ;  to  the  former  for  its  fresh  studies  in  their  own  field,  and  to  the  latter  for  its  fresh 
proof  that  they  have  still  a  field  to  cultivate.  The  book,  so  far  as  we  know,  is  the  most 
elaborate  and  comprehensive  attempt  yet  made  in  the  English  language  to  give  all  the 
data  which  are  claimed  to  connect  the  nervous  system  with  the  phenomena  of  conscious- 
ness, in  a  way  to  lay  the  foundation  for  an  explanation  of  mind  in  terms  of  matter.  The 
book  is  fully  illustrated,  and  well  indexed."— W.  K  Evangelist. 

OUTLINES  OF   PHYSIOLOGICAL   PSYCHOLOGY 

A  Text-book  of  Mental  Science  for  Academies  and  Colleges 
Crown  8vo.    505  pages.    $2.00 

The  volume  is  not  an  abridgment  or  revision  of  the  larger  book, 
Elements  of  Physiological  Psychology,  which  is  still  to  be  preferred  for 
mature  students,  but,  like  it,  surveys  the  entire  field,  though  with  less  de- 
tails and  references  that  might  embarrass  beginners.  Briefer  discussions 
of  the  nervous  mechanism,  and  of  the  nature  of  the  mind  as  related  to 
the  body,  will  be  found  in  the  "  Outlines  "  ;  while  the  treatment  of  rela- 
tions existing  between  excited  organs  and  mental  phenomena  offers  much 
new  material,  especially  on  "Consciousness,"  "Memory,"  and  "  Will." 
The  author  aims  to  furnish  a  complete  yet  correct  text-book  for  the  brief 
study  of  mental  phenomena,  from  the  experimental  and  physiological 
point  of  view.  Both  pupil  and  teacher  have  been  considered,  that  the 
book  may  be  readily  learned  and  successfully  taught. 

"  We  regard  it  as  even  better  than  the  larger  work,  as  it  is  more  judicious  and  mature, 
having  the  advantages  of  longer  reflection  upon  the  subject  and  larger  experience  in  teach- 
ing it.     For  its  purpose  there  is  not  a  better  text-book  in  the  language." — The  Nation. 

"He  has  discharged  his  task  with  great  thoroughness,  with  a  lightness  of  touch,  and  a 
clearness  and  precision  of  style  that  come  only  from  perfect  mastery  of  the  matter  in  hand. 
The  book  fills,  and  fills  solidly,  a  great  gap  in  our  psychological  literature.  "—J.  G. 
ScHURMAN,  Cornell  University. 


METAPHYSICAL   PSYCHOLOGY 


PHILOSOPHY  OF   MIND 

Aa  Essay  In  the  Metaphysics  of  Psychology.    8vo.    412  pagac.    %i.*» 

This  is  a  speculative  treatment  of  certain  problems  suggested,  but 
not  discussed,  in  the  study  of  psychology,  and  therefore  appropriately ' 
follows  the  author's  earlier  works  on  that  subject.  The  subjects  treated 
are  :  Psychology  and  the  Philosophy  of  Mind,  The  Concept  of  Mind, 
The  Reality  of  Mind,  The  Consciousness  of  Identity  and  the  so-called 
Double  Consciousness,  The  Unity  of  Mind,  Mind  and  Body,  Materialism 
and  Spiritualism,  Monism  and  Dualism,  Origin  and  Permanence  of  Mind, 
Place  of  Man's  Mind  in  Nature. 

JOURNAL  OF  MENTAL  SCIENCE,  London.— "We  may  say  of  this  book  that  it 
is  written  in  the  author's  best  style.  The  destructive  criticism  is  in  places  markedly 
effective,  and  the  book  ought  to  be  widely  read  as  one  of  the  most  able  and  suggestive 
contributions  of  recent  years  to  the  literature  of  the  philosophy  of  mind." 

THE  DIAL.—"  Its  raking  attack  upon  over-hasty  monism  is  particularly  well  timed. 
Although  the  border-land  which  divides  Psychology  from  Metaphysics  is  partially  sur- 
veyed in  manv  philosophical  and  psychological  works.  Professor  Ladd  has  for  the  first 
time  brought  the  more  important  questions  within  the  limits  of  a  single  volume." 

PHILOSOPHY   OF    KNOWLEDGE 

8vo.    614  pages.    $4.00 

This  is  the  first  adequate  discussion  of  the  subject  by  any  American 
author,  and  naturally  will  attract  special  attention  aside  from  the  fact  that 
it  is  the  work  of  Dr.  Ladd,  whose  name  is  so  familiar  to  students  of 
philosophy  both  in  this  country  and  abroad.  The  book  appeals  to  the 
general  reader  by  reason  of  the  relation  this  subject  bears  to  questions 
now  so  prominently  before  the  philosophical  and  religious  world,  as  well 
as  through  the  broad  sympathy  of  the  author  with  different  phases  of 
thought.  It  will  also  find  a  place  waiting  for  it  as  a  text-book  for 
advanced  and  postgraduate  students  in  the  study  of  logic  and  the  laws 
of  thought.  Ministers,  too,  will  get  from  it  much  material  for  which 
they  find  a  constant  use. 

THE  PHILOSOPHICAL  REVIEW.— "It  would  ill  become  one  to  take  leave  of  a  work 
which  must  lay  many  under  obligation  without  noting  its  broad  basis  in  a  knowledge 
carefully  garnered  from  many  sources  during  long  years,  its  candor,  its  striking  variety  of 
content,  and  its  suggestiveness." 

Copies  of  these  books  will  be  supplied  to  teachers  for  examination  or  intro- 
duction at  Special  Net  Rates,  regarding  which  correspondence  is  solicited. 


CHARLES  5CRIBNER'S  SONS 

PUBLISHERS  -  -  NEW  YORK  CITY 


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